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a
FEATURES Controls and Monitors up to 4 Fan Speeds 1 On-Chip and 2 Remote Temperature Sensors Dynamic TMIN Control Mode Optimizes System Acoustics Intelligently Automatic Fan Speed Control Mode Controls System Cooling Based on Measured Temperature Enhanced Acoustic Mode Dramatically Reduces User Perception of Changing Fan Speeds Thermal Protection Feature via THERM Output Monitors Performance Impact of Intel(R) Pentium(R) 4 Processor Thermal Control Circuit via THERM Input 2-Wire and 3-Wire Fan Speed Measurement Limit Comparison of All Monitored Values Meets SMBus 2.0 Electrical Specifications (Fully SMBus 1.1 Compliant) APPLICATIONS Low Acoustic Noise PCs Networking and Telecommunications Equipment
dBCOOLTM Remote Thermal Controller and Fan Controller ADT7460*
GENERAL DESCRIPTION
The ADT7460 dBCOOL controller is a thermal monitor and multiple PWM fan controller for noise-sensitive applications requiring active system cooling. It can monitor the temperature of up to two remote sensor diodes, plus its own internal temperature. It can measure and control the speed of up to four fans so that they operate at the lowest possible speed for minimum acoustic noise. The automatic fan speed control loop optimizes fan speed for a given temperature. A unique dynamic TMIN control mode enables the system thermals/acoustics to be intelligently managed. The effectiveness of the system's thermal solution can be monitored using the THERM input. The ADT7460 also provides critical thermal protection to the system using the bidirectional THERM pin as an output to prevent system or component overheating.
FUNCTIONAL BLOCK DIAGRAM
ADDR SELECT ADDR EN SCL SDA SMBALERT
SMBUS ADDRESS SELECTION AUTOMATIC FAN SPEED CONTROL
SERIAL BUS INTERFACE ADDRESS POINTER REGISTER
PWM1 PWM2 PWM3
PWM REGISTERS AND CONTROLLERS
ACOUSTIC ENHANCEMENT CONTROL
TACH1 TACH2 TACH3 TACH4 PERFORMANCE MONITORING THERM VCC TO ADT7460 THERMAL PROTECTION FAN SPEED COUNTER
DYNAMIC TMIN CONTROL
PWM CONFIGURATION REGISTERS
INTERRUPT MASKING
INTERRUPT STATUS REGISTERS
VCC D1+ D1- D2+ D2- +2.5VIN
ADT7460
INPUT SIGNAL CONDITIONING AND ANALOG MULTIPLEXER 10-BIT ADC LIMIT COMPARATORS
BAND GAP TEMP. SENSOR GND
BAND GAP REFERENCE
VALUE AND LIMIT REGISTERS
*Protected by U.S. Patent Nos. 6,188,189; 6,169,442; 6,097,239; 5,982,221; and 5,867,012. Other patents pending.
REV. B
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective companies.
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ADT7460-SPECIFICATIONS1, 2, 3, 4
Parameter POWER SUPPLY Supply Voltage Supply Current, ICC TEMPERATURE-TO-DIGITAL CONVERTER Local Sensor Accuracy Resolution Remote Diode Sensor Accuracy Min 3.0
(TA = TMIN to TMAX, VCC = VMIN to VMAX, unless otherwise noted.)
Typ 5.0 Max 5.5 3 20 1.5 3 0.25 1.5 2.5 3 0.25 180 11 Unit V mA A C C C C C C C A A Test Conditions/Comments
Interface Inactive, ADC Active Standby Mode 0 C TA 70 C -40 C TA +120 C 0C 0C 0C TA TA TA 70 C; 0 C TD 105 C; 0 C TD 120 C; 0 C TD 120 C 120 C 120 C
Resolution Remote Sensor Source Current ANALOG-TO-DIGITAL CONVERTER (INCLUDING MUX AND ATTENUATORS) Total Unadjusted Error, TUE Differential Nonlinearity, DNL Power Supply Sensitivity Conversion Time (Voltage Input) Conversion Time (Local Temperature) Conversion Time (Remote Temperature) Total Monitoring Cycle Time Input Resistance FAN RPM-TO-DIGITAL CONVERTER Accuracy 80
High Level Low Level
0.1 11.38 12.09 25.59 120.17 13.51 140
1.5 1 13 13.50 28 134.50 15 200 7 11 13 65,535
% LSB %/V ms ms ms ms ms k % % % RPM RPM RPM RPM kHz
8 Bits Averaging Enabled Averaging Enabled Averaging Enabled Averaging Enabled (Incl. Delay5) Averaging Disabled
0 C TA 70 C 0 C TA 105 C -40 C TA +120 C Fan Count = 0xBFFF Fan Count = 0x3FFF Fan Count = 0x0438 Fan Count = 0x021C
Full-Scale Count Nominal Input RPM
Internal Clock Frequency OPEN-DRAIN DIGITAL OUTPUTS, PWM1-PWM3, XTO Current Sink, IOL Output Low Voltage, VOL High Level Output Current, IOH OPEN-DRAIN SERIAL DATA BUS OUTPUT (SDA) Output Low Voltage, VOL High Level Output Current, IOH SMBUS DIGITAL INPUTS (SCL, SDA) Input High Voltage, VIH Input Low Voltage, VIL Hysteresis DIGITAL INPUT LOGIC LEVELS (TACH INPUTS) Input High Voltage, VIH Input Low Voltage, VIL
82.8
109 329 5000 10000 90.0
97.2
0.1
8.0 0.4 1
mA V A
IOUT = -8.0 mA, VCC = 3.3 V VOUT = VCC
0.1
0.4 1
V A
IOUT = -4.0 mA, VCC = 3.3 V VOUT = VCC
2.0 0.4 500
V V mV
2.0 5.5 +0.8 -0.3 0.5 -2-
Hysteresis
V V V V V p-p
Maximum Input Voltage Minimum Input Voltage
REV. B
ADT7460
Parameter DIGITAL INPUT LOGIC LEVELS (THERM) Input High Voltage, VIH Input Low Voltage, VIL DIGITAL INPUT CURRENT Input High Current, IIH Input Low Current, IIL Input Capacitance, CIN SERIAL BUS TIMING Clock Frequency, fSCLK Glitch Immunity, tSW Bus Free Time, tBUF Start Setup Time, tSU;STA Start Hold Time, tHD;STA SCL Low Time, tLOW SCL High Time, tHIGH SCL, SDA Rise Time, tR SCL, SDA Fall Time, tF Data Setup Time, tSU;DAT Data Hold Time, tHD;DAT Detect Clock Low Timeout, tTIMEOUT
6
Min 1.7
Typ
Max
Unit V V A A pF kHz ns s s s s s ns s ns ns ms
Test Conditions/Comment
0.8 -1 +1 5 400 50 1.3 0.6 0.6 1.3 0.6
VIN = VCC VIN = 0
50 1000 300
100 300 15
35
See Figure 1 See Figure 1 See Figure 1 See Figure 1 See Figure 1 See Figure 1 See Figure 1 See Figure 1 See Figure 1 See Figure 1 See Figure 1 Can Be Optionally Disabled
NOTES 1 All voltages are measured with respect to GND, unless otherwise specified. 2 Typicals are at T A = 25C and represent the most likely parametric norm. 3 Logic inputs will accept input high voltages up to VMAX even when the device is operating down to VMIN. 4 Timing specifications are tested at logic levels of VIL = 0.8 V for a falling edge and V IH = 2.0 V for a rising edge. 5 The delay is the time between the round robin finishing one set of measurements and starting the next. 6 Guaranteed by design, not production tested. Specifications subject to change without notice.
tR tLOW
SCL
tF tHD;STA
tHD;STA
SDA
tHD;DAT
tHIGH tSU;DAT
tSU;STA
tSU;STO
tBUF
P S
S
P
Figure 1. Diagram for Serial Bus Timing
REV. B
-3-
ADT7460
ABSOLUTE MAXIMUM RATINGS* THERMAL CHARACTERISTICS
Positive Supply Voltage (VCC) . . . . . . . . . . . . . . . . . . . . . 6.5 V Voltage on Any Other Input or Output Pin . . . . -0.3 V to +6.5 V Input Current at Any Pin . . . . . . . . . . . . . . . . . . . . . . . 5 mA Package Input Current . . . . . . . . . . . . . . . . . . . . . . . 20 mA Maximum Junction Temperature (TJ max) . . . . . . . . . . 150C Storage Temperature Range . . . . . . . . . . . . -65C to +150C Lead Temperature, Soldering IR Reflow Peak Temperature . . . . . . . . . . . . . . . . . . . 220C Lead Temperature (soldering 10 sec) . . . . . . . . . . . . . 300C ESD Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1500 V
*Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
16-Lead QSOP Package: JA = 150C/W, JC = 39C/W
ORDERING GUIDE
Model
Temperature Range
Package Description 16-Lead QSOP 16-Lead QSOP 16-Lead QSOP
Package Option RQ-16 RQ-16 RQ-16
ADT7460ARQ -40 C to +120 C ADT7460ARQ-REEL -40 C to +120 C ADT7460ARQ-REEL7 -40 C to +120 C EVAL-ADT7460EB
CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the ADT7460 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
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REV. B
ADT7460
PIN CONFIGURATION
SCL 1 GND 2 VCC 3 TACH3 4 PWM2/SMBALERT 5
16 15 14
SDA PWM1/XTO +2.5VIN/SMBALERT D1+
ADT7460
13
TOP VIEW 12 D1- (Not to Scale) TACH1 6 11 D2+
7 8 10 9
TACH2 PWM3/ADDRESS ENABLE
D2- TACH4/ADDRESS SELECT/THERM
PIN FUNCTION DESCRIPTIONS
Pin No. Mnemonic
1 2 3 SCL GND VCC
Description
Digital Input (Open Drain). SMBus serial clock input. Requires SMBus pull-up. Ground Pin for the ADT7460. Power Supply. Can be powered by 3.3 V standby if monitoring in low power states is required. VCC is also monitored through this pin. The ADT7460 can also be powered from a 5 V supply. Setting Bit 7 of Configuration Register 1 (Reg. 0x40) rescales the VCC input attenuators to correctly measure a 5 V supply. Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 3. Can be reconfigured as an analog input (AIN3) to measure the speed of 2-wire fans. Digital Output (Open Drain). Requires 10 k typical pull-up. Pulsewidth modulated output to control Fan 2 speed. Digital Output (Open Drain). This pin may be reconfigured as an SMBALERT interrupt output to signal out-of-limit conditions. Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 1. Can be reconfigured as an analog input (AIN1) to measure the speed of 2-wire fans. Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 2. Can be reconfigured as an analog input (AIN2) to measure the speed of 2-wire fans. Digital I/O (Open Drain). Pulsewidth modulated output to control Fan 3/4 speed. Requires 10 k typical pull-up. If pulled low on power-up, this places the ADT7460 into address select mode, and the state of Pin 9 will determine the ADT7460's slave address. Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 4. Can be reconfigured as an analog input (AIN4) to measure the speed of 2-wire fans. If in address select mode, this pin determines the SMBus device address.
4 5
TACH3 PWM2 SMBALERT TACH1 TACH2 PWM3 ADDRESS ENABLE TACH4 ADDRESS SELECT THERM
6 7 8
9
10 11 12 13 14
15 16
Alternatively, the pin may be reconfigured as a bidirectional THERM pin. Can be used to time and monitor assertions on the THERM input. For example, can be connected to the PROCHOT output of Intel's Pentium 4 processor or to the output of a trip point temperature sensor. Can be used as an output to signal overtemperature conditions. D2- Cathode Connection to Second Thermal Diode. D2+ Anode Connection to Second Thermal Diode. D1- Cathode Connection to First Thermal Diode. D1+ Anode Connection to First Thermal Diode. +2.5VIN Analog Input. Monitors 2.5 V supply, typically a chipset voltage. SMBALERT Digital Output (Open Drain). This pin may be reconfigured as an SMBALERT interrupt output to signal out-of-limit conditions. PWM1/XTO Digital Output (Open Drain). Pulsewidth modulated output to control Fan 1 speed. Requires 10 k typical pull-up. SDA Digital I/O (Open Drain). SMBus bidirectional serial data. Requires SMBus pull-up.
REV. B
-5-
ADT7460
FUNCTIONAL DESCRIPTION General Description INTERNAL REGISTERS OF THE ADT7460
The ADT7460 is a thermal monitor and multiple fan controller for any system requiring monitoring and cooling. The device communicates with the system via a serial System Management Bus (SMBus). The serial bus controller has an optional address line for device selection (Pin 9), a serial data line for reading and writing addresses and data (Pin 16), and an input line for the serial clock (Pin 1). All control and programming functions of the ADT7460 are performed over the serial bus. In addition, two of the pins can be reconfigured as an SMBALERT output to indicate out-of-limit conditions.
Measurement Inputs
A brief description of the ADT7460's principal internal registers is given below. More detailed information on the function of each register is given in Tables IV to XLI.
Configuration Registers
The configuration registers provide control and configuration of the ADT7460, including alternate pinout functionality.
Address Pointer Register
This register contains the address that selects one of the other internal registers. When writing to the ADT7460, the first byte of data is always a register address, which is written to the address pointer register.
Status Registers
The device has three measurement inputs, one for voltage and two for temperature. It can also measure its own supply voltage and can measure ambient temperature with its on-chip temperature sensor. Pin 14 is an analog input with an on-chip attenuator and is configured to monitor 2.5 V. Power is supplied to the chip via Pin 3, and the system also monitors VCC through this pin. In PCs, this pin is normally connected to a 3.3 V standby supply. This pin can, however, be connected to a 5 V supply and monitor it without overranging. Remote temperature sensing is provided by the D1 and D2 inputs, to which diode-connected, external temperature-sensing transistors, such as a 2N3904 or CPU thermal diode, may be connected. The ADC also accepts input from an on-chip band gap temperature sensor that monitors system ambient temperature.
Sequential Measurement
These registers provide the status of each limit comparison and are used to signal out-of-limit conditions on the temperature, voltage, or fan speed channels. If Pin 14 is configured as SMBALERT, then this pin will assert low whenever an unmasked status bit gets set.
Interrupt Mask Registers
These registers allow each interrupt status event to be masked when Pin 14 is configured as an SMBALERT output.
Value and Limit Registers
The results of analog voltage input, temperature, and fan speed measurements are stored in these registers, along with their limit values.
Offset Registers
These registers allow each temperature channel reading to be offset by a twos complement value written to these registers.
TMIN Registers
When the ADT7460 monitoring sequence is started, it cycles sequentially through the measurement of 2.5 V input and the temperature sensors. Measured values from these inputs are stored in value registers. These can be read out over the serial bus, or can be compared with programmed limits stored in the limit registers. The results of out-of-limit comparisons are stored in the Status registers, which can be read over the serial bus to flag out-of-limit conditions.
ADT7460 Address Selection
These registers program the starting temperature for each fan under automatic fan speed control.
TRANGE Registers
These registers program the temperature-to-fan speed control slope in automatic fan speed control mode for each PWM output.
Operating Point Registers
Pin 8 is the dual function PWM3/ADDRESS ENABLE pin. If Pin 8 is pulled low on power-up, the ADT7460 will read the state of Pin 9 (TACH4/ADDRESS SELECT/THERM) to determine the ADT7460's slave address. If Pin 8 is high on power-up, then the ADT7460 will default to SMBus slave address 0x2E. This function is described in more detail later.
These registers define the target operating temperatures for each thermal zone when running under dynamic TMIN control. This function allows the cooling solution to adjust dynamically in response to measured temperature and system performance.
Enhance Acoustics Registers
These registers allow each PWM output controlling fan to be tweaked to enhance the system's acoustics.
-6-
REV. B
Typical Performance Characteristics-ADT7460
15
3
REMOTE TEMPERATURE ERROR - C
3
REMOTE TEMPERATURE ERROR - C
10 5 0 -5 DXP TO VCC (3.3V) -10 -15 -20 DXP TO GND
-3 -6 -9 -12 -15 -18 -21 -24 -27 -30 -33 -36 1
REMOTE TEMPERATURE ERROR ( C)
REMOTE TEMPERATURE ERROR - C
0
2
HIGH LIMIT
1 +3 SIGMA 0 -3 SIGMA -1 LOW LIMIT
-2
1
10.0 30.0 3.3 LEAKAGE RESISTANCE - M
100.0
2.2 3.3 4.7 10.0 22.0 DXP-DXN CAPACITANCE - nF
47.0
-3 -40
10 60 TEMPERATURE - C
110
TPC 1. Remote Temperature Error vs. Leakage Resistance
TPC 2. Remote Temperature Error vs. Capacitance between D+ and D-
TPC 3. Remote Temperature Error vs. Actual Temperature
3
14
12.5
REMOTE TEMPERATURE ERROR - C
LOCAL TEMPERATURE ERROR - C
2 1 0
HIGH LIMIT
12 10 8 6 4 2 0 -2.0 100k 100mV 250mV
LOCAL TEMPERATURE ERROR - C
10.0 7.5 250mV 5.0 2.5 0 -2.5 -5.0 100k 100mV
+3 SIGMA
-3 SIGMA -1
-2 LOW LIMIT -3 -40 10 60 TEMPERATURE - C 110
5M 550k FREQUENCY - Hz
50M
5M 550k FREQUENCY - Hz
50M
TPC 4. Local Temperature Error vs. Actual Temperature
TPC 5. Remote Temperature Error vs. Power Supply Noise Frequency
TPC 6. Local Temperature Error vs. Power Supply Noise Frequency
1.40
REMOTE TEMPERATURE ERROR - C
16
REMOTE TEMPERATURE ERROR - C
40 20mV 35 100mV 30 25 20 15 10 5 0 -5 -10 10k 100k 1M FREQUENCY - Hz 10M 20mV 40mV
1.45
SUPPLY CURRENT - mA
14 12 10 8 6 4 2 0 -2.0 60k 110k
1.50 1.55 1.60 1.65 1.70 1.75 1.80 1.85 1.90 2.6 2.5 3.0 3.4 3.8 4.2 4.6 5.0 SUPPLY VOLTAGE - V 5.4 5.5
10mV
1M 10M FREQUENCY - Hz
50M
TPC 7. Supply Current vs. Supply Voltage
TPC 8. Remote Temperature Error vs. Differential Mode Noise Frequency
TPC 9. Remote Temperature Error vs. Common-Mode Noise Frequency
REV. B
-7-
ADT7460
FRONT CHASSIS FAN
ADT7460
TACH2 PWM1 TACH1 PWM3 TACH3 D2+ D2- THERM PROCHOT SDA SCL SMBALERT GND
REAR CHASSIS FAN
AMBIENT TEMPERATURE
D1+ D1-
Figure 2. Recommended Implementation
RECOMMENDED IMPLEMENTATION
Configuring the ADT7460 as in Figure 2 allows the systems designer the following features: * Two PWM outputs for fan control of up to three fans (the front and rear chassis fans are connected in parallel). * Three TACH fan speed measurement inputs. * VCC measured internally through Pin 3. * CPU temperature measured using Remote 1 temperature channel.
* Ambient temperature measured through Remote 2 temperature channel. * Bidirectional THERM pin. Allows Intel Pentium 4 PROCHOT monitoring and can function as an overtemperature THERM output. * SMBALERT system interrupt output.
-8-
REV. B
ADT7460
SERIAL BUS INTERFACE
Control of the ADT7460 is carried out using the serial System Management Bus (SMBus). The ADT7460 is connected to this bus as a slave device, under the control of a master controller. The ADT7460 has a 7-bit serial bus address. When the device is powered up with Pin 8 (PWM3/ADDRESS ENABLE) high, the ADT7460 will have a default SMBus address of 0101110 or 0x2E. If more than one ADT7460 is to be used in a system, then each ADT7460 should be placed in address select mode by strapping Pin 8 low on power-up. The logic state of Pin 9 then determines the device's SMBus address. The logic state of these pins is sampled upon power-up. The device address is sampled and latched on the first valid SMBus transaction, more precisely, on the low-to-high transition at the beginning of the eighth SCL pulse, when the serial address byte matches the selected slave address. The selected slave address is chosen using the ADDRESS ENABLE/ADDRESS SELECT pins. Any attempted changes in the address will have no effect after this.
Table I. Address Select Mode
condition and shift in the next eight bits, consisting of a 7-bit address (MSB first) plus a R/W bit, which determines the direction of the data transfer, i.e., whether data will be written to or read from the slave device.
VCC
ADT7460
ADDR_SEL 9
10k
PWM3/ADDR_EN
8 ADDRESS = 0x2D
Figure 5. SMBus Address = 0x2D (Pin 9 = 1)
VCC
ADT7460
ADDR_SEL 9
10k
8 PWM3/ADDR_EN
NC DO NOT LEAVE ADDR_EN UNCONNECTED. CAN CAUSE UNPREDICTABLE ADDRESSES
Pin 8 State 0 0 1
Pin 9 State Low (10 k to GND) High (10 k Pull-Up) Don't Care
Address 0101100 (0x2C) 0101101 (0x2D) 0101110 (0x2E) (Default)
ADT7460
ADDR_SEL 9
VCC
CARE SHOULD BE TAKEN TO ENSURE THAT PIN 8 (PWM3/ADDR_EN) IS EITHER TIED HIGH OR LOW. LEAVING PIN 8 FLOATING COULD CAUSE THE ADT7460 TO POWER UP WITH AN UNEXPECTED ADDRESS. NOTE THAT IF THE ADT7460 IS PLACED INTO ADDRESS SELECT MODE, PINS 8 AND 9 CAN BE USED AS THE ALTERNATE FUNCTIONS (PWM3, TACH4/THERM) ONLY IF THE CORRECT CIRCUIT IS MUXED IN AT THE CORRECT TIME
10k
Figure 6. Unpredictable SMBus Address if Pin 8 Is Unconnected
8 PWM3/ADDR_EN ADDRESS = 0x2E
Figure 3. Default SMBus Address = 0x2E
ADT7460
ADDR_SEL 9 10k
The peripheral whose address corresponds to the transmitted address responds by pulling the data line low during the low period before the ninth clock pulse, known as the Acknowledge Bit. All other devices on the bus now remain idle while the selected device waits for data to be read from or written to it. If the R/W bit is a 0, then the master will write to the slave device. If the R/W bit is a 1, the master will read from the slave device. 2. Data is sent over the serial bus in sequences of nine clock pulses, eight bits of data followed by an Acknowledge Bit from the slave device. Transitions on the data line must occur during the low period of the clock signal and remain stable during the high period, as a low-to-high transition when the clock is high may be interpreted as a stop signal. The number of data bytes that can be transmitted over the serial bus in a single read or write operation is limited only by what the master and slave devices can handle. 3. When all data bytes have been read or written, stop conditions are established. In write mode, the master will pull the data line high during the 10th clock pulse to assert a stop condition. In read mode, the master device will override the acknowledge bit by pulling the data line high during the low period before the ninth clock pulse. This is known as No Acknowledge. The master will then take the data line low during the low period before the 10th clock pulse, then high during the 10th clock pulse to assert a stop condition.
PWM3/ADDR_EN
8 ADDRESS = 0x2C
Figure 4. SMBus Address = 0x2C (Pin 9 = 0)
The facility to make hardwired changes to the SMBus slave address allows the user to avoid conflicts with other devices sharing the same serial bus, for example, if more than one ADT7460 is used in a system. The serial bus protocol operates as follows: 1. The master initiates data transfer by establishing a start condition, defined as a high-to-low transition on the serial data line SDA while the serial clock line SCL remains high. This indicates that an address/data stream will follow. All slave peripherals connected to the serial bus respond to the start
REV. B
-9-
ADT7460
1 SCL 9 1 9
SDA START BY MASTER
0
1
0
1
1
A1
A0
R/W ACK. BY ADT7460
D7
D6
D5
D4
D3
D2
D1
D0 ACK. BY ADT7460
FRAME 1 SERIAL BUS ADDRESS BYTE
FRAME 2 ADDRESS POINTER REGISTER BYTE 1 9
SCL (CONTINUED)
SDA (CONTINUED)
D7
D6
D5
D4
D3
D2
D1
D0 ACK. BY ADT7460 STOP BY MASTER
FRAME 3 DATA BYTE
Figure 7. Writing a Register Address to the Address Pointer Register, Then Writing Data to the Selected Register
Any number of bytes of data may be transferred over the serial bus in one operation, but it is not possible to mix read and write in one operation because the type of operation is determined at the beginning and cannot subsequently be changed without starting a new operation. In the case of the ADT7460, write operations contain either one or two bytes, and read operations contain one byte and perform the following functions: To write data to one of the device data registers or read data from it, the address pointer register must be set so that the correct data register is addressed, then data can be written into
that register or read from it. The first byte of a write operation always contains an address that is stored in the address pointer register. If data is to be written to the device, then the write operation contains a second data byte that is written to the register selected by the address pointer register. This is illustrated in Figure 7. The device address is sent over the bus followed by R/W being set to 0. This is followed by two data bytes. The first data byte is the address of the internal data register to be written to, which is stored in the address pointer register. The second data byte is the data to be written to the internal data register.
-10-
REV. B
ADT7460
1 SCL 9 1 9
SDA START BY MASTER
0
1
0
1
1
A1
A0
R/W ACK. BY ADT7460
D7
D6
D5
D4
D3
D2
D1
D0 ACK. BY ADT7460 STOP BY MASTER
FRAME 1 SERIAL BUS ADDRESS BYTE
FRAME 2 ADDRESS POINTER REGISTER BYTE
Figure 8. Writing to the Address Pointer Register Only
1 SCL 9 1 9
SDA START BY MASTER
0
1
0
1
1
A1
A0
R/W ACK. BY ADT7460
D7
D6
D5
D4
D3
D2
D1
D0 NO ACK. BY STOP BY MASTER MASTER
FRAME 1 SERIAL BUS ADDRESS BYTE
FRAME 2 DATA BYTE FROM ADT7460
Figure 9. Reading Data from a Previously Selected Register
When reading data from a register, there are two possibilities: 1. If the ADT7460's address pointer register value is unknown or not the desired value, it is first necessary to set it to the correct value before data can be read from the desired data register. This is done by performing a write to the ADT7460 as before, but only the data byte containing the register address is sent as data is not to be written to the register. This is shown in Figure 8. A read operation is then performed consisting of the serial bus address, R/W bit set to 1, followed by the data byte read from the data register. This is shown in Figure 9. 2. If the address pointer register is known to be already at the desired address, data can be read from the corresponding data register without first writing to the address pointer register, so Figure 8 can be omitted.
Notes
1. It is possible to read a data byte from a data register without first writing to the address pointer register if the address pointer register is already at the correct value. However, it is not possible to write data to a register without writing to the address pointer register because the first data byte of a write is always written to the address pointer register. 2. In Figures 7 to 9, the serial bus address is shown as the default value 01011(A1)(A0), where A1 and A0 are set by the address select mode function previously defined. 3. In addition to supporting the Send Byte and Receive Byte protocols, the ADT7460 also supports the Read Byte protocol (see System Management Bus specifications Rev. 2.0 for more information). 4. If it is required to perform several read or write operations in succession, the master can send a repeat start condition instead of a stop condition to begin a new operation.
REV. B
-11-
ADT7460
ADT7460 WRITE OPERATIONS ADT7460 READ OPERATIONS
The SMBus specification defines several protocols for different types of read and write operations. The ones used in the ADT7460 are discussed below. The following abbreviations are used in the diagrams: S - START P - STOP R - READ W - WRITE A - ACKNOWLEDGE A - NO ACKNOWLEDGE The ADT7460 uses the following SMBus write protocols:
Send Byte
The ADT7460 uses the following SMBus read protocols:
Receive Byte
In this operation, the master device sends a single command byte to a slave device as follows: 1. The master device asserts a start condition on SDA. 2. The master sends the 7-bit slave address followed by the write bit (low). 3. The addressed slave device asserts ACK on SDA. 4. The master sends a command code. 5. The slave asserts ACK on SDA. 6. The master asserts a stop condition on SDA and the transaction ends. For the ADT7460, the send byte protocol is used to write a register address to RAM for a subsequent single byte read from the same address. This is illustrated in Figure 10.
1 S 2 3 4 REGISTER ADDRESS 56 AP
This is useful when repeatedly reading a single register. The register address needs to have been set up previously. In this operation, the master device receives a single byte from a slave device as follows: 1. The master device asserts a start condition on SDA. 2. The master sends the 7-bit slave address followed by the read bit (high). 3. The addressed slave device asserts ACK on SDA. 4. The master receives a data byte. 5. The master asserts NO ACK on SDA. 6. The master asserts a stop condition on SDA and the transaction ends. In the ADT7460, the receive byte protocol is used to read a single byte of data from a register whose address has previously been set by a send byte or write byte operation.
1 2 3 4 REGISTER ADDRESS 56 AP
S SLAVE W A ADDRESS
Figure 12. Single Byte Read from a Register
ALERT RESPONSE ADDRESS
SLAVE W A ADDRESS
Alert response address (ARA) is a feature of SMBus devices that allows an interrupting device to identify itself to the host when multiple devices exist on the same bus. The SMBALERT output can be used as an interrupt output or can be used as an SMBALERT. One or more outputs can be connected to a common SMBALERT line connected to the master. If a device's SMBALERT line goes low, the following procedure occurs: 1. SMBALERT is pulled low. 2. Master initiates a read operation and sends the alert response address (ARA = 0001 100). This is a general call address that must not be used as a specific device address. 3. The device whose SMBALERT output is low responds to the alert response address, and the master reads its device address. The address of the device is now known, and it can be interrogated in the usual way. 4. If more than one device's SMBALERT output is low, the one with the lowest device address will have priority in accordance with normal SMBus arbitration. 5. Once the ADT7460 has responded to the alert response address, the master must read the status registers and the SMBALERT will be cleared only if the error condition has gone away.
Figure 10. Setting a Register Address for Subsequent Read
If it is required to read data from the register immediately after setting up the address, the master can assert a repeat start condition immediately after the final ACK and carry out a single byte read without asserting an intermediate stop condition.
Write Byte
In this operation, the master device sends a command byte and one data byte to the slave device as follows: 1. The master device asserts a start condition on SDA. 2. The master sends the 7-bit slave address followed by the write bit (low). 3. The addressed slave device asserts ACK on SDA. 4. The master sends a command code. 5. The slave asserts ACK on SDA. 6. The master sends a data byte. 7. The slave asserts ACK on SDA. 8. The master asserts a stop condition on SDA to end the transaction. This is illustrated in Figure 11.
1 2 3 4 REGISTER ADDRESS 5 6 78
S SLAVE W A ADDRESS
A DATA A P
Figure 11. Single Byte Write to a Register
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REV. B
ADT7460
SMBus Timeout INPUT CIRCUITRY
The ADT7460 includes an SMBus timeout feature. If there is no SMBus activity for 35 ms, the ADT7460 assumes that the bus is locked and releases the bus. This prevents the device from locking or holding the SMBus expecting data. Some SMBus controllers cannot handle the SMBus timeout feature, so it can be disabled.
CONFIGURATION REGISTER 1 (REG. 0x40)
The internal structure for the 2.5 V analog input is shown in Figure 13. The input circuit consists of an input protection diode, an attenuator, plus a capacitor to form a first order low-pass filter that gives the input immunity to high frequency noise.
VOLTAGE MEASUREMENT REGISTERS
Reg. 0x20 2.5 V Reading = 0x00 Default <6> TODIS = 0; SMBus Timeout Enabled (Default) <6> TODIS = 1; SMBus Timeout Disabled
VOLTAGE MEASUREMENT INPUT 2.5 V LIMIT REGISTERS
The ADT7460 has one external voltage measurement channel. It can also measure its own supply voltage, VCC. Pin 14 may be configured to measure a 2.5 V supply. The VCC supply voltage measurement is carried out through the VCC pin (Pin 3). Setting Bit 7 of Configuration Register 1 (Reg. 0x40) allows a 5 V supply to power the ADT7460 and be measured without overranging the VCC measurement channel. The 2.5 V input can be used to monitor a chipset supply voltage in computer systems.
ANALOG-TO-DIGITAL CONVERTER
Associated with the 2.5 V measurement channel is a high and low limit register. Exceeding the programmed high or low limit causes the appropriate status bit to be set. Exceeding either limit can also generate SMBALERT interrupts. Reg. 0x44 2.5 V Low Limit = 0x00 Default Reg. 0x45 2.5 V High Limit = 0xFF Default
45k 2.5VIN 94k 30pF
Figure 13. Structure of Analog Inputs
All analog inputs are multiplexed into the on-chip, successive approximation, analog-to-digital converter. This has a resolution of 10 bits. The basic input range is 0 V to 2.25 V, but the input has built-in attenuators to allow measurement of 2.5 V without any external components. To allow for the tolerance of the supply voltage, the ADC produces an output of 3/4 full scale (decimal 768 or 300 hex) for the nominal input voltage and so has adequate headroom to deal with overvoltages.
Table II shows the input ranges of the analog inputs and output codes of the 10-bit ADC. When the ADC is running, it samples and converts a voltage input in 711 s and averages 16 conversions to reduce noise; a measurement takes nominally 11.38 ms.
REV. B
-13-
ADT7460
Table II. 10-Bit A/D Output Code vs. VIN
Input Voltage +5VIN <0.0065 0.0065-0.0130 0.0130-0.0195 0.0195-0.0260 0.0260-0.0325 0.0325-0.0390 0.0390-0.0455 0.0455-0.0521 0.0521-0.0586 * * * 1.6675-1.6740 * * * 3.3300-3.3415 * * * 5.0025-5.0090 * * * 6.5983-6.6048 6.6048-6.6113 6.6113-6.6178 6.6178-6.6244 6.6244-6.6309 6.6309-6.6374 6.6374-6.4390 6.6439-6.6504 6.6504-6.6569 6.6569-6.6634 >6.6634 VCC (3.3VIN)* <0.0042 0.0042-0.0085 0.0085-0.0128 0.0128-0.0171 0.0171-0.0214 0.0214-0.0257 0.0257-0.0300 0.0300-0.0343 0.0343-0.0386 * * * 1.1000-1.1042 * * * 2.2000-2.2042 * * * 3.3000-3.3042 * * * 4.3527-4.3570 4.3570-4.3613 4.3613-4.3656 4.3656-4.3699 4.3699-4.3742 4.3742-4.3785 4.3785-4.3828 4.3828-4.3871 4.3871-4.3914 4.3914-4.3957 >4.3957 +2.5VIN <0.0032 0.0032-0.0065 0.0065-0.0097 0.0097-0.0130 0.0130-0.0162 0.0162-0.0195 0.0195-0.0227 0.0227-0.0260 0.0260-0.0292 * * * 0.8325-0.8357 * * * 1.6650-1.6682 * * * 2.4975-2.5007 * * * 3.2942-3.2974 3.2974-3.3007 3.3007-3.3039 3.3039-3.3072 3.3072-3.3104 3.3104-3.3137 3.3137-3.3169 3.3169-3.3202 3.3202-3.3234 3.3234-3.3267 >3.3267 Decimal
A/D Output Binary (10 Bits) 00000000 00 00000000 01 00000000 10 00000000 11 00000001 00 00000001 01 00000001 10 00000001 11 00000010 00 * * * 01000000 00 * * * 10000000 00 * * * 11000000 00 * * * 11111101 01 11111101 10 11111101 11 11111110 00 11111110 01 11111110 10 11111110 11 11111111 00 11111111 01 11111111 10 11111111 11 0 1 2 3 4 5 6 7 8 * * * 256 (1/4 scale) * * * 512 (1/2 scale) * * * 768 (3/4 scale) * * * 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023
*The VCC output codes listed assume that V CC is 3.3 V. If V CC input is reconfigured for 5 V operation (by setting Bit 7 of Configuration Register 1), then the VCC output codes are the same as for the 5 V IN column.
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ADT7460
ADDITIONAL ADC FUNCTIONS FOR VOLTAGE MEASUREMENTS TEMPERATURE MEASUREMENT SYSTEM Local Temperature Measurement
A number of other functions are available on the ADT7460 to offer the systems designer increased flexibility:
Turn-Off Averaging
For each voltage measurement read from a value register, 16 readings have actually been made internally and the results averaged before being placed into the value register. There may be an instance where you would like to speed up conversions. Setting Bit 4 of Configuration Register 2 (Reg. 0x73) turns averaging off. This effectively gives a reading 16 times faster (711 s), but the reading may be noisier.
Bypass Voltage Input Attenuator
The ADT7460 contains an on-chip band gap temperature sensor whose output is digitized by the on-chip 10-bit ADC. The 8-bit MSB temperature data is stored in the local temperature register (Address 0x26). As both positive and negative temperatures can be measured, the temperature data is stored in twos complement format, as shown in Table III. Theoretically, the temperature sensor and ADC can measure temperatures from -128 C to +127 C with a resolution of 0.25 C. However, this exceeds the operating temperature range of the device, so local temperature measurements outside this range are not possible.
Remote Temperature Measurement
Setting Bit 5 of Configuration Register 2 (Reg. 0x73) removes the attenuation circuitry from the 2.5 V input. This allows the user to directly connect external sensors or rescale the analog voltage measurement inputs for other applications. The input range of the ADC without the attenuators is 0 V to 2.25 V.
Single-Channel ADC Conversion
The ADT7460 can measure the temperature of two remote diode sensors or diode-connected transistors connected to Pins 12 and 13, or Pins 10 and 11. The forward voltage of a diode or diode-connected transistor operated at a constant current exhibits a negative temperature coefficient of about -2 mV/ C. Unfortunately, the absolute value of VBE varies from device to device and individual calibration is required to null this out, so the technique is unsuitable for mass production. The technique used in the ADT7460 is to measure the change in VBE when the device is operated at two different currents. This is given by VBE = KT q x ln(N ) where: K is Boltzmann's constant. q is the charge on the carrier. T is the absolute temperature in Kelvins. N is the ratio of the two currents. Figure 14 shows the input signal conditioning used to measure the output of a remote temperature sensor. This figure shows the external sensor as a substrate transistor, provided for temperature monitoring on some microprocessors. It could equally well be a discrete transistor, such as a 2N3904.
Setting Bit 6 of Configuration Register 2 (Reg. 0x73) places the ADT7460 into single-channel ADC conversion mode. In this mode, the ADT7460 can be made to read a single voltage channel only. If the internal ADT7460 clock is used, the selected input will be read every 711 s. The appropriate ADC channel is selected by writing to Bits <7:5> of the TACH1 Minimum High Byte Register (0x55). Bits <7:5> Reg. 0x55 000 010 Channel Selected 2.5 V VCC
Configuration Register 2 (Reg. 0x73)
<4> = 1 Averaging Off <5> = 1 Bypass Input Attenuators <6> = 1 Single-Channel Convert Mode
TACH1 Minimum High Byte (Reg. 0x55)
<7:5> Selects ADC Channel for Single-Channel Convert Mode
VDD I CPU N I IBIAS
THERMDA REMOTE SENSING TRANSISTOR
D+
VOUT+ TO ADC
THERMDC
D- BIAS DIODE LOW PASS FILTER fC = 65kHz
VOUT-
Figure 14. Signal Conditioning for Remote Diode Temperature Sensors
REV. B
-15-
ADT7460
If a discrete transistor is used, the collector will not be grounded, and should be linked to the base. If a PNP transistor is used, the base is connected to the D- input and the emitter to the D+ input. If an NPN transistor is used, the emitter is connected to the D- input and the base to the D+ input. Figures 15a and 15b show how to connect the ADT7460 to an NPN or PNP transistor for temperature measurement. To prevent ground noise from interfering with the measurement, the more negative terminal of the sensor is not referenced to ground but is biased above ground by an internal diode at the D- input. To measure VBE, the sensor is switched between operating currents of I and N I. The resulting waveform is passed through a 65 kHz low-pass filter to remove noise and to a chopperstabilized amplifier that performs the functions of amplification and rectification of the waveform to produce a dc voltage proportional to VBE. This voltage is measured by the ADC to give a temperature output in 10-bit, twos complement format. To further reduce the effects of noise, digital filtering is performed by averaging the results of 16 measurement cycles. A remote temperature measurement takes nominally 25.5 ms. The results of remote temperature measurements are stored in 10-bit, twos complement format, as illustrated in Table III. The extra resolution for the temperature measurements is held in the Extended Resolution Register 2 (Reg. 0x77). This gives temperature readings with a resolution of 0.25 C.
Table III. Temperature Data Format
ADT7460
2N3904 NPN D+ D-
Figure 15a. Measuring Temperature Using an NPN Transistor
ADT7460
D+ 2N3906 PNP D-
Figure 15b. Measuring Temperature Using a PNP Transistor
Nulling Out Temperature Errors
Temperature -128 C -125 C -100 C -75 C -50 C -25 C -10 C 0C +10.25 C +25.5 C +50.75 C +75 C +100 C +125 C +127 C
Digital Output (10-Bit)* 1000 0000 00 1000 0011 00 1001 1100 00 1011 0101 00 1100 1110 00 1110 0111 00 1111 0110 00 0000 0000 00 0000 1010 01 0001 1001 10 0011 0010 11 0100 1011 00 0110 0100 00 0111 1101 00 0111 1111 00
As CPUs run faster, it is getting more difficult to avoid high frequency clocks when routing the D+, D- traces around a system board. Even when recommended layout guidelines are followed, there may still be temperature errors attributed to noise being coupled onto the D+/D- lines. High frequency noise generally has the effect of giving temperature measurements that are too high by a constant amount. The ADT7460 has temperature offset registers at Addresses 0x70, 0x72 for the Remote 1 and Remote 2 temperature channels. By doing a one-time calibration of the system, one can determine the offset caused by system board noise and null it out using the offset registers. The offset registers automatically add a twos complement 8-bit reading to every temperature measurement. The LSB adds 0.25C offset to the temperature reading so the 8-bit register effectively allows temperature offsets of up to 32 C with a resolution of 0.25 C. This ensures that the readings in the temperature measurement registers are as accurate as possible.
Temperature Offset Registers
Reg. 0x70 Remote 1 Temp Offset = 0x00 (0C Default) Reg. 0x71 Local Temp Offset = 0x00 (0C Default) Reg. 0x72 Remote 2 Temp Offset = 0x00 (0C Default)
*Bold denotes 2 LSBs of measurement in Extended Resolution Register 2 (Reg. 0x77) with 0.25 C resolution.
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ADT7460
TEMPERATURE MEASUREMENT REGISTERS SINGLE-CHANNEL ADC CONVERSIONS
Reg. 0x25 Remote 1 Temperature = 0x80 Default Reg. 0x26 Local Temperature = 0x80 Default Reg. 0x27 Remote 2 Temperature = 0x80 Default Reg. 0x77 Extended Resolution 2 = 0x00 Default <7:6> TDM2 = Remote 2 Temperature LSBs <5:4> LTMP = Local Temperature LSBs <3:2> TDM1 = Remote 1 Temperature LSBs
Temperature Measurement Limit Registers
Setting Bit 6 of Configuration Register 2 (Reg. 0x73) places the ADT7460 into single-channel ADC conversion mode. In this mode, the ADT7460 can be made to read a single temperature channel only. The appropriate ADC channel is selected by writing to Bits <7:5> of TACH1 Minimum High Byte Register (0x55). Bits <7:5> Reg. 0x55 101 110 111 Channel Selected Remote 1 Temp Local Temp Remote 2 Temp
Associated with each temperature measurement channel are high and low limit registers. Exceeding the programmed high or low limit causes the appropriate status bit to be set. Exceeding either limit can also generate SMBALERT interrupts. Reg. 0x4E Remote 1 Temp Low Limit = 0x81 Default Reg. 0x4F Remote 1 Temp High Limit = 0x7F Default Reg. 0x50 Local Temp Low Limit = 0x81 Default Reg. 0x51 Local Temp High Limit = 0x7F Default Reg. 0x52 Remote 2 Temp Low Limit = 0x81 Default Reg. 0x53 Remote 2 Temp High Limit = 0x7F Default
Reading Temperature from the ADT7460
Configuration Register 2 (Reg. 0x73)
<4> = 1 Averaging Off <6> = 1 Single-Channel Convert Mode
TACH1 Minimum High Byte (Reg. 0x55)
<7:5> Selects ADC Channel for Single-Channel Convert Mode
Overtemperature Events
It is important to note that temperature can be read from the ADT7460 as an 8-bit value (with 1C resolution), or as a 10-bit value (with 0.25C resolution). If only 1C resolution is required, the temperature readings can be read back at any time and in no particular order. If the 10-bit measurement is required, this involves a 2-register read for each measurement. The Extended Resolution Register (Reg. 0x77) should be read first. This causes all temperature reading registers to be frozen until all temperature reading registers have been read from. This prevents an MSB reading from being updated while its 2 LSBs are being read, and vice versa.
ADDITIONAL ADC FUNCTIONS FOR TEMPERATURE MEASUREMENT
Overtemperature events on any of the temperature channels can be detected and dealt with automatically in automatic fan speed control mode. Registers 0x6A-0x6C are the THERM limits. When a temperature exceeds its THERM limit, all fans will run at 100% duty cycle. The fans will stay running at 100% until the temperature drops below THERM - Hysteresis (this can be disabled by setting the BOOST bit in Configuration Register 3, Bit 2, Register 0x78). The hysteresis value for that THERM limit is the value programmed into Registers 0x6D, 0x6E (hysteresis registers). The default hysteresis value is 4C.
THERM LIMIT
HYSTERESIS = ( C) TEMP
FANS
100%
A number of other functions are available on the ADT7460 to offer the systems designer increased flexibility:
Turn-Off Averaging
Figure 16. THERM Limit Operation
For each temperature measurement read from a value register, 16 readings have actually been made internally and the results averaged before being placed into the value register. Sometimes it may be necessary to take a very fast measurement, e.g., of CPU temperature. Setting Bit 4 of Configuration Register 2 (Reg. 0x73) turns averaging off. This takes a reading every 15.5 ms. Each remote temperature measurement takes 4 ms and the local temperature measurement takes 1.4 ms.
REV. B
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ADT7460
LIMITS, STATUS REGISTERS, AND INTERRUPTS Limit Values Out-of-Limit Comparisons
Associated with each measurement channel on the ADT7460 are high and low limits. These can form the basis of system status monitoring: a status bit can be set for any out-of-limit condition and detected by polling the device. Alternatively, SMBALERT interrupts can be generated to flag a processor or microcontroller of out-of-limit conditions.
8-Bit Limits
Once all limits have been programmed, the ADT7460 can be enabled for monitoring. The ADT7460 will measure all parameters in round-robin format and set the appropriate status bit for out-of-limit conditions. Comparisons are done differently depending on whether the measured value is being compared to a high or low limit. HIGH LIMIT: > COMPARISON PERFORMED LOW LIMIT: < OR = COMPARISON PERFORMED
The following is a list of 8-bit limits on the ADT7460:
Voltage Limit Registers
Reg. 0x44 2.5 V Low Limit = 0x00 Default Reg. 0x45 2.5 V High Limit = 0xFF Default Reg. 0x48 VCC Low Limit = 0x00 Default Reg. 0x49 VCC High Limit = 0xFF Default
Temperature Limit Registers
NO INT
Reg. 0x4E Remote 1 Temp Low Limit = 0x81 Default Reg. 0x4F Remote 1 Temp High Limit = 0x7F Default Reg. 0x6A Remote 1 THERM Limit = 0x64 Default Reg. 0x50 Local Temp Low Limit = 0x81 Default Reg. 0x51 Local Temp High Limit = 0x7F Default Reg. 0x6B Local THERM Limit = 0x64 Default Reg. 0x52 Remote 2 Temp Low Limit = 0x81 Default Reg. 0x53 Remote 2 Temp High Limit = 0x7F Default Reg. 0x6C Remote 2 THERM Limit = 0x64 Default
THERM Limit Register
TEMP > LOW LIMIT LOW LIMIT
Reg. 0x7A THERM Timer Limit = 0x00 Default
16-Bit Limits
Figure 17. Temperature > Low Limit: No INT
The fan TACH measurements are 16-bit results. The fan TACH limits are also 16 bits, consisting of a high byte and low byte. Since fans running under speed or stalled are normally the only conditions of interest, only high limits exist for fan TACHs. Since fan TACH period is actually being measured, exceeding the limit indicates a slow or stalled fan.
Fan Limit Registers
Reg. 0x54 TACH1 Minimum Low Byte = 0xFF Default Reg. 0x55 TACH1 Minimum High Byte = 0xFF Default Reg. 0x56 TACH2 Minimum Low Byte = 0xFF Default Reg. 0x57 TACH2 Minimum High Byte = 0xFF Default Reg. 0x58 TACH3 Minimum Low Byte = 0xFF Default Reg. 0x59 TACH3 Minimum High Byte = 0xFF Default Reg. 0x5A TACH4 Minimum Low Byte = 0xFF Default Reg. 0x5B TACH4 Minimum High Byte = 0xFF Default
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REV. B
ADT7460
Analog Monitoring Cycle Time
INT
The analog monitoring cycle begins when a 1 is written to the start bit (Bit 0) of Configuration Register 1 (Reg 0x40). The ADC measures each analog input in turn and as each measurement is completed, the result is automatically stored in the appropriate value register. This round-robin monitoring cycle continues unless disabled by writing a 0 to Bit 0 of Configuration Register 1. As the ADC will normally be left to free-run in this manner, the time taken to monitor all the analog inputs will normally not be of interest, as the most recently measured value of any input can be read out at any time. For applications where the monitoring cycle time is important, it can easily be calculated.
LOW LIMIT
TEMP = LOW LIMIT
The total number of channels measured is * Two supply voltage inputs (2.5 V and VCC) * Local temperature * Two remote temperatures As mentioned previously, the ADC performs round-robin conversions and takes 11.38 ms for each voltage measurement, 12 ms for a local temperature reading, and 25.5 ms for each remote temperature reading. The total monitoring cycle time for averaged voltage and temperature monitoring is, therefore, nominally
Figure 18. Temperature = Low Limit: INT Occurs
NO INT
(2 x 11.38) + 12 + (2 x 25.5) = 85.76 ms
HIGH LIMIT
The round robin starts again 35 ms later. Therefore, all channels are measured approximately every 120 ms. Fan TACH measurements are made in parallel and are not synchronized with the analog measurements in any way.
TEMP = HIGH LIMIT
Status Registers
Figure 19. Temperature = High Limit: No INT
The results of limit comparisons are stored in Status Registers 1 and 2. The status register bit for each channel reflects the status of the last measurement and limit comparison on that channel. If a measurement is within limits, the corresponding status register bit will be cleared to 0. If the measurement is out-of-limits, the corresponding status register bit will be set to 1. The state of the various measurement channels may be polled by reading the status registers over the serial bus. In Bit 7 (OOL) of Status Register 1 (Reg. 0x41), 1 means that an out-of-limit event has been flagged in Status Register 2. This means that you need only read Status Register 2 when this bit is set. Alternatively, Pin 5 or Pin 14 can be configured as an SMBALERT output. This will automatically notify the system supervisor of an out-of-limit condition. Reading the status registers clears the appropriate status bit as long as the error condition that caused the interrupt has cleared. Status register bits are "sticky." Whenever a status bit gets set, indicating an out-of-limit condition, it will remain set even if the event that caused it has gone away (until read). The only way to clear the status bit is to read the status register after the event has gone away. Interrupt status mask registers (Reg. 0x74, 0x75) allow individual interrupt sources to be masked from causing an SMBALERT. However, if one of these masked interrupt sources goes out-of-limit, its associated status bit will get set in the interrupt status registers.
INT
HIGH LIMIT
TEMP > HIGH LIMIT
Figure 20. Temperature > High Limit: INT Occurs
REV. B
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ADT7460
HIGH LIMIT
TEMPERATURE
OOL = 1 DENOTES A PARAMETER MONITORED THROUGH STATUS REG 2 IS OUT-OF-LIMIT
Figure 21. Status Register 1
Status Register 1 (Reg. 0x41)
"STICKY" STATUS BIT SMBALERT
CLEARED ON READ (TEMP BELOW LIMIT) TEMP BACK IN LIMIT (STATUS BIT STAYS SET)
Bit 7 (OOL) = 1, denotes a bit in Status Register 2 is set and Status Register 2 should be read. Bit 6 (R2T) = 1, Remote 2 temp high or low limit has been exceeded. Bit 5 (LT) = 1, Local temp high or low limit has been exceeded. Bit 4 (R1T) = 1, Remote 1 temp high or low limit has been exceeded. Bit 3 = Unused Bit 2 (VCC) = 1, VCC high or low limit has been exceeded. Bit 1 = Unused Bit 0 (2.5 V) = 1, 2.5 V high or low limit has been exceeded.
Figure 23. SMBALERT and Status Bit Behavior
Figure 23 shows how the SMBALERT output and sticky status bits behave. Once a limit is exceeded, the corresponding status bit gets set to 1. The status bit remains set until the error condition subsides and the status register gets read. The status bits are referred to as sticky since they remain set until read by software. This ensures that an out-of-limit event cannot be missed if software is polling the device periodically. Note that the SMBALERT output remains low for the entire duration that a reading is out-of-limit and until the status register has been read. This has implications on how software handles the interrupt.
HANDLING SMBALERT INTERRUPTS
To prevent the system from being tied up servicing interrupts, it is recommend to handle the SMBALERT interrupt as follows: 1. Detect the SMBALERT assertion.
F4P = 1, FAN4 OR THERM TIMER IS OUT-OF-LIMIT
2. Enter the interrupt handler. 3. Read the status registers to identify the interrupt source. 4. Mask the interrupt source by setting the appropriate mask bit in the interrupt mask registers (Reg. 0x74, 0x75). 5. Take the appropriate action for a given interrupt source. 6. Exit the interrupt handler. 7. Periodically poll the status registers. If the interrupt status bit has cleared, reset the corresponding interrupt mask bit to 0. This will cause the SMBALERT output and status bits to behave as shown in Figure 24.
HIGH LIMIT
Figure 22. Status Register 2
Status Register 2 (Reg. 0x42)
Bit 7 (D2) = 1, indicates an open or short on D2+/D2- inputs. Bit 6 (D1) = 1, indicates an open or short on D2+/D2- inputs. Bit 5 (F4P) = 1, indicates Fan 4 has dropped below minimum speed. Alternatively, indicates that THERM timer limit has been exceeded if the THERM timer function is used. Bit 4 (FAN3) = 1, indicates Fan 3 has dropped below minimum speed. Bit 3 (FAN2) = 1, indicates Fan 2 has dropped below minimum speed. Bit 2 (FAN1) = 1, indicates Fan 1 has dropped below minimum speed. Bit 1 (OVT) = 1, indicates that a THERM overtemperature limit has been exceeded. Bit 0 = Unused
SMBALERT Interrupt Behavior
TEMPERATURE
STICKY STATUS BIT
CLEARED ON READ (TEMP BELOW LIMIT) TEMP BACK IN LIMIT (STATUS BIT STAYS SET)
The ADT7460 can be polled for status, or an SMBALERT interrupt can be generated for out-of-limit conditions. It is important to note how the SMBALERT output and status bits behave when writing interrupt handler software.
SMBALERT
INTERRUPT MASK BIT SET INTERRUPT MASK BIT CLEARED (SMBALERT REARMED)
Figure 24. How Masking the Interrupt Source Affects SMBALERT Output
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REV. B
ADT7460
Masking Interrupt Sources THERM as an Input
Interrupt Mask Registers 1 and 2 are located at Addresses 0x74 and 0x75. These allow individual interrupt sources to be masked out to prevent SMBALERT interrupts. Note that masking an interrupt source only prevents the SMBALERT output from being asserted; the appropriate status bit will get set as normal.
Interrupt Mask Register 1 (Reg. 0x74)
When configured as an input, the THERM pin allows the user to time assertions on the pin. This can be useful for connecting to the PROCHOT output of a CPU to gauge system performance. See this data sheet for more information on timing THERM assertions and generating SMBALERTs based on THERM. The user can also set up the ADT7460 so when the THERM pin is driven low externally the fans will run at 100%. The fans will run at 100% for the duration of the THERM pin being pulled low. This is done by setting the BOOST bit (Bit 2) in Configuration Register 3 (Address = 0x78) to 1. This works only if the fan is already running, for example, in manual mode when the current duty cycle is above 0x00 or in automatic mode when the temperature is above TMIN. If the temperature is below TMIN or if the duty cycle in manual mode is set to 0x00, then pulling the THERM low externally will have no effect. See Figure 25 for more information.
Bit 7 (OOL) = 1, masks SMBALERT for any alert condition flagged in Status Register 2. Bit 6 (R2T) = 1, masks SMBALERT for Remote 2 temperature. Bit 5 (LT) = 1, masks SMBALERT for local temperature. Bit 4 (R1T) = 1, masks SMBALERT for Remote 1 temperature. Bit 3 = Unused Bit 2 (VCC) = 1, masks SMBALERT for VCC channel. Bit 1 = Unused Bit 0 (2.5 V) = 1, masks SMBALERT for 2.5 V channel.
Interrupt Mask Register 2 (Reg. 0x75)
Bit 7 (D2) = 1, masks SMBALERT for Diode 2 errors. Bit 6 (D1) = 1, masks SMBALERT for Diode 1 errors. Bit 5 (FAN4) = 1, masks SMBALERT for Fan 4 failure. If the TACH4 pin is being used as the THERM input, this bit masks SMBALERT for a THERM event. Bit 4 (FAN3) = 1, masks SMBALERT for Fan 3. Bit 3 (FAN2) = 1, masks SMBALERT for Fan 2. Bit 2 (FAN1) = 1, masks SMBALERT for Fan 1. Bit 1 (OVT) = 1, masks SMBALERT for overtemperature (exceeding THERM limits). Bit 0 = Unused
Enabling the SMBALERT Interrupt Output
TMIN
THERM
THERM ASSERTED LOW AS AN INPUT. FANS DO NOT GO TO 100% SINCE TEMPERATURE IS BELOW T MIN.
THERM ASSERTED LOW AS AN INPUT. FANS GO TO 100% SINCE TEMPERATURE IS ABOVE T MIN AND FANS ARE ALREADY RUNNING.
The SMBALERT interrupt function is disabled by default. Pin 5 or Pin 14 can be reconfigured as an SMBALERT output to signal out-of-limit conditions.
Configuring Pin 5 as SMBALERT Output
Figure 25. Asserting THERM Low as an Input in Automatic Fan Speed Control Mode
THERM Timer
Register Config Reg 4 (Reg. 0x7D) Register Config Reg 4 (Reg. 0x7D)
Bit Setting <0> AL2.5V = 1 Bit Setting <0> AL2.5V = 1
Configuring Pin 14 as SMBALERT Output
The ADT7460 has an internal timer to measure THERM assertion time. For example, the THERM input may be connected to the PROCHOT output of a Pentium 4 CPU and measure system performance. The THERM input may also be connected to the output of a trip point temperature sensor. The timer is started on the assertion of the ADT7460's THERM input and stopped on the negation of the pin. The timer counts THERM times cumulatively, i.e., the timer resumes counting on the next THERM assertion. The THERM timer will continue to accumulate THERM assertion times until the timer is read (it is cleared on read) or until it reaches full scale. If the counter reaches full scale, it will stop at that reading until cleared. The 8-bit THERM timer register (Reg. 0x79) is designed such that Bit 0 will get set to 1 on the first THERM assertion. Once the cumulative THERM assertion time has exceeded 45.52 ms, Bit 1 of the THERM timer gets set and Bit 0 becomes the LSB of the timer with a resolution of 22.76 ms. Figure 26 illustrates how the THERM timer behaves as the THERM input is asserted and negated. Bit 0 gets set on the first THERM assertion detected. This bit remains set until such time as the cumulative THERM assertions exceed 45.52 ms. At this time, Bit 1 of the THERM timer gets set, and Bit 0 is cleared. Bit 0 now reflects timer readings with a resolution of 22.76 ms.
To Assign THERM Functionality to Pin 9
Pin 9 can be configured as the THERM pin on the ADT7460. To configure Pin 9 as the THERM pin, set the THERM ENABLE Bit (Bit 1) in Configuration Register 3 (Address = 0x78) = 1.
REV. B
-21-
ADT7460
THERM
* If the THERM timer is read during a THERM assertion a) The contents of the timer are cleared.
00000001 76543210 THERM ASSERTED 22.76ms
THERM TIMER (REG. 0x79)
b) Bit 0 of the THERM timer is set to 1 (since a THERM assertion is occurring). c) The THERM timer increments from zero. d) If the THERM limit (Reg. 0x7A) = 0x00, then the F4P bit gets set.
Generating SMBALERT Interrupts from THERM Events
THERM
ACCUMULATE THERM LOW ASSERTION TIMES THERM TIMER (REG. 0x79) 00000010 76543210 THERM ASSERTED 45.52ms
THERM
ACCUMULATE THERM LOW ASSERTION TIMES THERM TIMER 0 0 0 0 0 1 0 1 (REG. 0x79) 7 6 5 4 3 2 1 0
THERM ASSERTED 113.8ms (91.04ms + 22.76ms)
Figure 26. Understanding the THERM Timer
The ADT7460 can generate SMBALERTs when a programmable THERM limit has been exceeded. This allows the systems designer to ignore brief, infrequent THERM assertions while capturing longer THERM events. Register 0x7A is the THERM limit register. This 8-bit register allows a limit from 0 seconds (first THERM assertion) to 5.825 seconds to be set before an SMBALERT is generated. The THERM timer value is compared with the contents of the THERM limit register. If the THERM timer value exceeds the THERM limit value, then the F4P bit (Bit 5) of Status Register 2 gets set and an SMBALERT is generated. Note that the F4P bit (Bit 5) of Mask Register 2 (Reg. 0x75) will mask out SMBALERTs if this bit is set to 1, although the F4P bit of Interrupt Status Register 2 will still get set if the THERM limit is exceeded. Figure 27 is a Functional Block Diagram of the THERM timer, limit, and associated circuitry. Writing a value of 0x00 to the THERM limit register (Reg. 0x7A) causes SMBALERT to be generated on the first THERM assertion. A THERM limit value of 0x01 generates an SMBALERT once cumulative THERM assertions exceed 45.52 ms.
When using the THERM timer, be aware of the following: * After a THERM timer read (Reg. 0x79) a) The contents of the timer get cleared on read. b) The F4P bit (Bit 5) of Status Register 2 needs to be cleared (assuming the THERM limit has been exceeded).
THERM LIMIT (REG. 0x7A)
2.914s 1.457s 728.32ms 364.16ms 182.08ms 91.04ms 45.52ms 22.76ms
2.914s 1.457s 728.32ms 364.16ms 182.08ms 91.04ms 45.52ms 22.76ms
THERM TIMER (REG. 0x79)
01234567
76543210
THERM THERM TIMER CLEARED ON READ
COMPARATOR
IN
OUT
F4P BIT (BIT 5) STATUS REGISTER 2 SMBALERT
LATCH RESET CLEARED ON READ 1 = MASK
F4P BIT (BIT 5) MASK REGISTER 2 (REG. 0x75)
Figure 27. Functional Diagram of ADT7460's THERM Monitoring Circuitry
-22-
REV. B
ADT7460
Configuring the Desired THERM Behavior
1. Configure the THERM input. Setting Bit 1 (THERM ENABLE) of Configuration Register 3 (Reg. 0x78) enables the THERM monitoring function. 2. Select the desired fan behavior for THERM events. Setting Bit 2 (BOOST bit) of Configuration Register 3 (Reg. 0x78) causes all fans to run at 100% duty cycle whenever THERM gets asserted. This allows fail-safe system cooling. If this bit = 0, the fans will run at their current settings and will not be affected by THERM events. 3. Select whether THERM events should generate SMBALERT interrupts. Bit 5 (F4P) of Mask Register 2 (Reg. 0x75), when set, masks out SMBALERTs when the THERM limit value gets exceeded. This bit should be cleared if SMBALERTs based on THERM events are required. 4. Select a suitable THERM limit value. This value determines whether an SMBALERT is generated on the first THERM assertion, or only if a cumulative THERM assertion time limit is exceeded. A value of 0x00 causes an SMBALERT to be generated on the first THERM assertion. 5. Select a THERM monitoring time. This is how often OS or BIOS level software checks the THERM timer. For example, BIOS could read the THERM timer once an hour to determine the cumulative THERM assertion time. If, for example, the total THERM assertion time is <22.76 ms in Hour 1, >182.08 ms in Hour 2, and >5.825 s in Hour 3, this can indicate that system performance is degrading significantly since THERM is asserting more frequently on an hourly basis. Alternatively, OS or BIOS level software can time-stamp when the system is powered on. If an SMBALERT is generated due to the THERM limit being exceeded, another time-stamp can be taken. The difference in time can be calculated for a fixed THERM limit time. For example, if it takes one week for a THERM limit of 2.914 s to be exceeded and the next time it takes only one hour, then this is an indication of a serious degradation in system performance.
Configuring the ADT7460 THERM Pin as an Output
THERM LIMIT +0.25 C THERM LIMIT
TEMP
THERM
ADT7460 MONITORING CYCLE
Figure 28. Asserting THERM as an Output, Based on Tripping THERM Limits
FAN DRIVE USING PWM CONTROL
The ADT7460 uses pulsewidth modulation (PWM) to control fan speed. This relies on varying the duty cycle (or on/off ratio) of a square wave applied to the fan to vary the fan speed. The external circuitry required to drive a fan using PWM control is extremely simple. A single NMOSFET is the only drive device required. The specifications of the MOSFET depend on the maximum current required by the fan being driven. Typical notebook fans draw a nominal 170 mA, and so SOT devices can be used where board space is a concern. In desktops, fans can typically draw 250 mA-300 mA each. If you drive several fans in parallel from a single PWM output or drive larger server fans, the MOSFET will need to handle the higher current requirements. The only other stipulation is that the MOSFET should have a gate voltage drive, VGS < 3.3 V for direct interfacing to the PWM_OUT pin. VGS can be greater than 3.3 V as long as the pull-up on the gate is tied to 5 V. The MOSFET should also have a low on resistance to ensure that there is not significant voltage drop across the FET. This would reduce the voltage applied across the fan and therefore the maximum operating speed of the fan. Figure 29 shows how a 3-wire fan may be driven using PWM control.
12V 12V
In addition to the ADT7460 being able to monitor THERM as an input, the ADT7460 can optionally drive THERM low as an output. The user can preprogram system critical thermal limits. If the temperature exceeds a thermal limit by 0.25C, THERM will assert low. If the temperature is still above the thermal limit on the next monitoring cycle, THERM will stay low. THERM will remain asserted low until the temperature is equal to or below the thermal limit. Since the temperature for that channel is only measured every monitoring cycle, once THERM asserts it is guaranteed to remain low for at least one monitoring cycle. The THERM pin can be configured to assert low if the Remote 1, local, or Remote 2 temperature THERM limits get exceeded by 0.25C. The THERM limit registers are at Locations 0x6A, 0x6B, and 0x6C, respectively. Setting Bit 3 of registers 0x5F, 0x60, and 0x61 enables the THERM output feature for the Remote 1, local, and Remote 2 temperature channels, respectively. Figure 28 shows how the THERM pin asserts low as an output in the event of a critical overtemperature.
10k 10k TACH/AIN TACH 4.7k 3.3V 10k PWM Q1 NDT3055L 12V FAN 1N4148
ADT7460
Figure 29. Driving a 3-Wire Fan Using an N-Channel MOSFET
Figure 29 uses a 10 k pull-up resistor for the TACH signal. This assumes that the TACH signal is open-collector from the fan. In all cases, the TACH signal from the fan must be kept below 5 V maximum to prevent damaging the ADT7460. If in doubt as to whether the fan used has an open-collector or totem pole TACH output, use one of the input signal conditioning circuits shown in the Fan Speed Measurement section of the data sheet.
REV. B
-23-
ADT7460
Figure 30 shows a fan drive circuit using an NPN transistor such as a general-purpose MMBT2222. While these devices are inexpensive, they tend to have much lower current handling capabilities and higher on-resistance than MOSFETs. When choosing a transistor, care should be taken to ensure that it meets the fan's current requirements. Ensure that the base resistor is chosen such that the transistor is saturated when the fan is powered on.
12V 12V
Driving Two Fans from PWM3
Note that the ADT7460 has four TACH inputs available for fan speed measurement, but only three PWM drive outputs. If a fourth fan is being used in the system, it should be driven from the PWM3 output in parallel with the third fan. Figure 31 shows how to drive two fans in parallel using low cost NPN transistors. Figure 32 is the equivalent circuit using the NDT3055L MOSFET. Note that since the MOSFET can handle up to 3.5 A, it is simply a matter of connecting another fan directly in parallel with the first. Care should be taken in designing drive circuits with transistors and FETs to ensure that the PWM pins are not required to source current and that they sink less than the 8 mA maximum current specified on the data sheet.
Driving Up to Three Fans from PWM2
10k 10k TACH/AIN TACH 4.7k 3.3V 470 PWM Q1 MMBT2222 12V FAN 1N4148
ADT7460
Figure 30. Driving a 3-Wire Fan Using an NPN Transistor
TACH measurements for fans are synchronized to particular PWM channels, e.g., TACH1 is synchronized to PWM1. TACH3 and TACH4 are both synchronized to PWM3, so PWM3 can drive two fans. Alternatively, PWM2 can be programmed to synchronize TACH2, TACH3, and TACH4 to the PWM2 output. This allows PWM2 to drive two or three fans. In this case, the drive circuitry looks the same as shown in Figures 30, 31, and 32. The SYNC bit in Register 0x62 enables this function.
12V 3.3V 3.3V TACH3 1k PWM3 2.2k Q1 MMBT3904 Q2 MMBT2222 Q3 MMBT2222
1N4148
ADT7460
TACH4
10
10
Figure 31. Interfacing Two Fans in Parallel to the PWM3 Output Using Low Cost NPN Transistors
3.3V 10k TYPICAL TACH4 3.3V +V 5V OR 12V FAN TACH 1N4148 TACH 3.3V 10k TYPICAL PWM3 Q1 NDT3055L 5V OR 12V FAN +V
ADT7460
TACH3
10k TYPICAL
Figure 32. Interfacing Two Fans in Parallel to the PWM3 Output Using a Single N-Channel MOSFET
-24-
REV. B
ADT7460
ENHANCE ACOUSTICS REGISTER 1 (REG. 0x62) LAYING OUT 2-WIRE AND 3-WIRE FANS
<4> SYNC = 1, Synchronizes TACH2, TACH3, and TACH4 to PWM2.
Driving 2-Wire Fans
Figure 35 shows how to lay out a common circuit arrangement for 2-wire and 3-wire fans. Some components will not be populated, depending on whether a 2-wire or 3-wire fan is being used.
12V OR 5V
Figure 33 shows how a 2-wire fan may be connected to the ADT7460. This circuit allows the speed of a 2-wire fan to be measured, even though the fan has no dedicated TACH signal. A series resistor, RSENSE, in the fan circuit converts the fan commutation pulses into a voltage. This is ac-coupled into the ADT7460 through the 0.01 F capacitor. On-chip signal conditioning allows accurate monitoring of fan speed. The value of RSENSE chosen depends upon the programmed input threshold and the current drawn by the fan. For fans drawing approximately 200 mA, a 2 RSENSE value is suitable when the threshold is programmed as 40 mV. For fans that draw more current, such as larger desktop or server fans, RSENSE may be reduced for the same programmed threshold. The smaller the threshold programmed the better, since more voltage will be developed across the fan and the fan will spin faster. Figure 34 shows a typical plot of the sensing waveform at a TACH/AIN pin. The most important thing is that the voltage spikes (either negative going or positive going) are more than 40 mV in amplitude. This allows fan speed to be reliably determined.
+V 5V OR 12V FAN 1N4148
R1
1N4148 3.3V OR 5V
R2
R5 PWM C1
TACH/AIN R3 R4
Q1 MMBT2222 FOR 3-WIRE FANS: POPULATE R1, R2, R3 R4 = 0 C1 = UNPOPULATED FOR 2-WIRE FANS: POPULATE R4, C1 R1, R2, R3 UNPOPULATED
Figure 35. Planning for 2-Wire or 3-Wire Fans on a PCB
TACH Inputs
Pins 4, 6, 7, and 9 are open-drain TACH inputs intended for fan speed measurement. Signal conditioning in the ADT7460 accommodates the slow rise and fall times typical of fan tachometer outputs. The maximum input signal range is 0 V to 5 V, even where VCC is less than 5 V. In the event that these inputs are supplied from fan outputs that exceed 0 V to 5 V, either resistive attenuation of the fan signal or diode clamping must be included to keep inputs within an acceptable range. Figures 36a to 36d show circuits for most common fan TACH outputs. If the fan TACH output has a resistive pull-up to VCC, it can be connected directly to the fan input, as shown in Figure 36a.
VCC 12V
ADT7460
3.3V 10k TYPICAL
PWM 0.01 F TACH/AIN
Q1 NDT3055L
RSENSE 2 TYPICAL
Figure 33. Driving a 2-Wire Fan
PULL-UP 4.7k TYP
ADT7460
TACH OUTPUT TACH FAN SPEED COUNTER
Figure 36a. Fan with TACH Pull-Up to VCC
If the fan output has a resistive pull-up to 12 V (or other voltage greater than 5 V), the fan output can be clamped with a Zener diode, as shown in Figure 36b. The Zener diode voltage should be chosen so that it is greater than VIH of the TACH input but less than 5 V, allowing for the voltage tolerance of the Zener. A value of between 3 V and 5 V is suitable.
Figure 34. Fan Speed Sensing Waveform at TACH/AIN Pin
REV. B
-25-
ADT7460
12V VCC
PULL-UP 4.7k TYP
ADT7460
TACH OUTPUT ZD1* TACH FAN SPEED COUNTER
measured by gating an on-chip 90 kHz oscillator into the input of a 16-bit counter for N periods of the fan TACH output (Figure 37), so the accumulated count is actually proportional to the fan tachometer period and inversely proportional to the fan speed.
CLOCK
PWM
*CHOOSE ZD1 VOLTAGE APPROX 0.8
VCC
TACH 1 2 3 4
Figure 36b. Fan with TACH Pull-Up to Voltage > 5 V, e.g., 12 V, Clamped with Zener Diode
If the fan has a strong pull-up (less than 1 k) to 12 V or a totem-pole output, then a series resistor can be added to limit the Zener current, as shown in Figure 36c. Alternatively, a resistive attenuator may be used, as shown in Figure 36d. R1 and R2 should be chosen such that: 2 V < VPULLUP x R2 / (RPULLUP + R1 + R2) < 5 V The fan inputs have an input resistance of nominally 160 k to ground, so this should be taken into account when calculating resistor values. With a pull-up voltage of 12 V and pull-up resistor less than 1 k, suitable values for R1 and R2 would be 100 k and 47 k. This will give a high input voltage of 3.83 V.
5V OR 12V FAN VCC
Figure 37. Fan Speed Measurement
N, the number of pulses counted, is determined by the settings of Register 0x7B (fan pulses per revolution register). This register contains two bits for each fan, allowing one, two (default), three, or four TACH pulses to be counted.
Fan Speed Measurement Registers
The fan tachometer readings are 16-bit values consisting of a 2-byte read from the ADT7460. Reg. 0x28 TACH1 Low Byte = 0x00 Default Reg. 0x29 TACH1 High Byte = 0x00 Default Reg. 0x2A TACH2 Low Byte = 0x00 Default Reg. 0x2B TACH2 High Byte = 0x00 Default Reg. 0x2C TACH3 Low Byte = 0x00 Default Reg. 0x2D TACH3 High Byte = 0x00 Default Reg. 0x2E TACH4 Low Byte = 0x00 Default Reg. 0x2F TACH4 High Byte = 0x00 Default
Reading Fan Speed from the ADT7460
PULL-UP TYP <1k OR TOTEM POLE
ADT7460
R1 10k TACH OUTPUT TACH ZD1 ZENER* FAN SPEED COUNTER
*CHOOSE ZD1 VOLTAGE APPROX 0.8
VCC
Figure 36c. Fan with Strong TACH Pull-Up to > VCC or Totem-Pole Output, Clamped with Zener and Resistor
12V VCC
If fan speeds are being measured, this involves a 2-register read for each measurement. The low byte should be read first. This causes the high byte to be frozen until both high and low byte registers have been read from. This prevents erroneous TACH readings. The fan tachometer reading registers report back the number of 11.11 s period clocks (90 kHz oscillator) gated to the fan speed counter, from the rising edge of the first fan TACH pulse to the rising edge of the third fan TACH pulse (assuming two pulses per revolution are being counted). Since the device is essentially measuring the fan TACH period, the higher the count value the slower the fan is actually running. A 16-bit fan tachometer reading of 0xFFFF indicates either that the fan has stalled or is running very slowly (<100 RPM).
HIGH LIMIT: > COMPARISON PERFORMED
ADT7460
<1k R1* TACH OUTPUT TACH R2* FAN SPEED COUNTER
*SEE TEXT
Figure 36d. Fan with Strong TACH Pull-Up to > VCC or Totem-Pole Output, Attenuated with R1/R2
Fan Speed Measurement
The fan counter does not count the fan TACH output pulses directly because the fan speed may be less than 1000 RPM and it would take several seconds to accumulate a reasonably large and accurate count. Instead, the period of the fan revolution is
Since the actual fan TACH period is being measured, exceeding a fan TACH limit by 1 will set the appropriate status bit and can be used to generate an SMBALERT.
-26-
REV. B
ADT7460
Fan TACH Limit Registers
00 = 1 Pulse per Revolution 01 = 2 Pulses per Revolution 10 = 3 Pulses per Revolution 11 = 4 Pulses per Revolution
2-Wire Fan Speed Measurements
The fan TACH limit registers are 16-bit values consisting of two bytes. Reg. 0x54 TACH1 Minimum Low Byte = 0xFF Default Reg. 0x55 TACH1 Minimum High Byte = 0xFF Default Reg. 0x56 TACH2 Minimum Low Byte = 0xFF Default Reg. 0x57 TACH2 Minimum High Byte = 0xFF Default Reg. 0x58 TACH3 Minimum Low Byte = 0xFF Default Reg. 0x59 TACH3 Minimum High Byte = 0xFF Default Reg. 0x5A TACH4 Minimum Low Byte = 0xFF Default Reg. 0x5B TACH4 Minimum High Byte = 0xFF Default
Fan Speed Measurement Rate
The ADT7460 is capable of measuring the speed of 2-wire fans, i.e., fans without TACH outputs. To do this, the fan must be interfaced as shown in the Fan Drive Circuitry section of this data sheet. In this case, the TACH inputs need to be reprogrammed as analog inputs, AIN.
CONFIGURATION REGISTER 2 (REG. 0x73)
The fan TACH readings are normally updated once every second. The FAST bit (Bit 3) of Configuration Register 3 (Reg. 0x78), when set, updates the fan TACH readings every 250 ms. If any of the fans are not being driven by a PWM channel but are powered directly from 5 V or 12 V, its associated dc bit in Configuration Register 3 should be set. This allows TACH readings to be taken on a continuous basis for fans connected directly to a dc source.
Calculating Fan Speed
Bit 3 (AIN4) = 1, Pin 9 is reconfigured to measure the speed of a 2-wire fan using an external sensing resistor and coupling capacitor. Bit 2 (AIN3) = 1, Pin 4 is reconfigured to measure the speed of a 2-wire fan using an external sensing resistor and coupling capacitor. Bit 1 (AIN2) = 1, Pin 7 is reconfigured to measure the speed of a 2-wire fan using an external sensing resistor and coupling capacitor. Bit 0 (AIN1) = 1, Pin 6 is reconfigured to measure the speed of a 2-wire fan using an external sensing resistor and coupling capacitor.
AIN Switching Threshold
Assuming a fan with a two pulses/revolution (and two pulses/ revolution being measured), fan speed is calculated by Fan Speed (RPM) = (90,000 where: Fan TACH Reading = 16-Bit Fan Tachometer Reading
Example:
60)/Fan TACH Reading
Having configured the TACH inputs as AIN inputs for 2-wire measurements, the user can select the sensing threshold for the AIN signal.
CONFIGURATION REGISTER 4 (REG. 0x7D)
TACH1 High Byte (Reg. 0x29) = 0x17 TACH1 Low Byte (Reg. 0x28) = 0xFF What is Fan 1 speed in RPM? Fan 1 TACH Reading = 0x17FF = 6143 Decimal RPM = (f 60)/Fan 1 TACH Reading RPM = (90000 60)/6143 Fan Speed = 879 RPM
Fan Pulses per Revolution
<3:2> AINL
These two bits define the input threshold for 2-wire fan speed measurements. 00 = 20 mV 01 = 40 mV 10 = 80 mV 11 = 130 mV
Fan Spin-Up
Different fan models can output either 1, 2, 3, or 4 TACH pulses per revolution. Once the number of fan TACH pulses has been determined, it can be programmed into the fan pulses per revolution register (Reg. 0x7B) for each fan. Alternatively, this register can be used to determine the number or pulses/revolution output by a given fan. By plotting fan speed measurements at 100% speed with different pulses/revolution setting, the smoothest graph with the lowest ripple determines the correct pulses/revolution value.
Fan Pulses per Revolution Register
The ADT7460 has a unique fan spin-up function. It will spin the fan at 100% PWM duty cycle until two TACH pulses are detected on the TACH input. Once two pulses have been detected, the PWM duty cycle will go to the expected running value, e.g., 33%. The advantage of this is that fans have different spin-up characteristics and will take different times to overcome inertia. The ADT7460 runs the fans just fast enough to overcome inertia and will be quieter on spin-up than fans programmed to spin-up for a given spin-up time.
Fan Start-Up Timeout
<1:0> FAN1 Default = 2 Pulses per Revolution <3:2> FAN2 Default = 2 Pulses per Revolution <5:4> FAN3 Default = 2 Pulses per Revolution <7:6> FAN4 Default = 2 Pulses per Revolution
To prevent false interrupts being generated as a fan spins up (since it is below running speed), the ADT7460 includes a fan start-up timeout function. This is the time limit allowed for two TACH pulses to be detected on spin-up. For example, if 2 seconds fan start-up timeout is chosen and no TACH pulses occur within 2 seconds of the start of spin-up, a fan fault is detected and flagged in the interrupt status registers.
REV. B
-27-
ADT7460
PWM1 CONFIGURATION (REG. 0x5C) PWM1 FREQUENCY REGISTERS (REG. 0x5F-0x61)
<2:0> SPIN
These bits control the start-up timeout for PWM1. 000 = No Start-Up Timeout 001 = 100 ms 010 = 250 ms (default) 011 = 400 ms 100 = 667 ms 101 = 1 s 110 = 2 s 111 = 4 s
<2:0> FREQ 000 = 11.0 Hz 001 = 14.7 Hz 010 = 22.1 Hz 011 = 29.4 Hz 100 = 35.3 Hz (Default) 101 = 44.1 Hz 110 = 58.8 Hz 111 = 88.2 Hz
Fan Speed Control
PWM2 CONFIGURATION (REG. 0x5D)
<2:0> SPIN
These bits control the start-up timeout for PWM2. 000 = No Start-Up Timeout 001 = 100 ms 010 = 250 ms (default) 011 = 400 ms 100 = 667 ms 101 = 1 s 110 = 2 s 111 = 4 s
PWM3 CONFIGURATION (REG. 0x5E)
The ADT7460 can control fan speed using two different modes. The first is automatic fan speed control mode. In this mode, fan speed is automatically varied with temperature and without CPU intervention, once initial parameters are set up. The advantage of this is that in the case of the system hanging the system is protected from overheating. The automatic fan speed control incorporates a feature called dynamic TMIN calibration. This feature reduces the design effort required to program the automatic fan speed control loop. For more information and how to program the automatic fan speed control loop and dynamic TMIN calibration, see the AN-613 Programming the Automatic Fan Speed Control Loop Application Note (http://www.analog.com/Uploaded Files/Application_Notes/ 331085006AN613_0.pdf). The second fan speed control method is manual fan speed control, which is described in the next paragraph.
Manual Fan Speed Control
<2:0> SPIN
These bits control the start-up timeout for PWM3. 000 = No Start-Up Timeout 001 = 100 ms 010 = 250 ms (default) 011 = 400 ms 100 = 667 ms 101 = 1 s 110 = 2 s 111 = 4 s
The ADT7460 allows the duty cycle of any PWM output to be manually adjusted. This can be useful if you wish to change fan speed in software or want to adjust PWM duty cycle output for test purposes. Bits <7:5> of Registers 0x5C-0x5E (PWM configuration) control the behavior of each PWM output.
PWM CONFIGURATION (REG. 0x5C-0x5E)
Disabling Fan Start-Up Timeout
Although fan start-up makes fan spin-ups much quieter than fixed-time spin-ups, the option exists to use fixed spin-up times. Bit 5 (FSPDIS) = 1 in Configuration Register 1 (Reg. 0x40) disables the spin-up for two TACH pulses. Instead, the fan will spin up for the fixed time as selected in Registers 0x5C-0x5E.
PWM Logic State
<7:5> BHVR 111 = Manual Mode Once under manual control, each PWM output may be manually updated by writing to Registers 0x30-0x32 (PWMx current duty cycle registers).
Programming the PWM Current Duty Cycle Registers
The PWM outputs can be programmed high for 100% duty cycle (noninverted) or low for 100% duty cycle (inverted).
PWM1 Configuration (Reg. 0x5C)
The PWM current duty cycle registers are 8-bit registers that allow the PWM duty cycle for each output to be set anywhere from 0% (0x00) to 100% (0xFF) in steps of 0.39% (256 steps). The value to be programmed into the PWMMIN register is given by Value(decimal ) = PWM MIN 0.39 Example 1: For a PWM duty cycle of 50%, Value (decimal) = 50/0.39 = 128 Decimal Value = 128 Decimal or 0x80. Example 2: For a PWM duty cycle of 33%, Value (decimal) = 33/0.39 = 85 Decimal Value = 85 Decimal or 0x54.
<4> INV
0 = Logic High for 100% PWM Duty Cycle 1 = Logic Low for 100% PWM Duty Cycle 0 = Logic High for 100% PWM Duty Cycle 1 = Logic Low for 100% PWM Duty Cycle 0 = Logic High for 100% PWM Duty Cycle 1 = Logic Low for 100% PWM Duty Cycle
PWM2 Configuration (Reg. 0x5D)
<4> INV
PWM3 Configuration (Reg. 0x5E)
<4> INV
PWM Drive Frequency
The PWM drive frequency can be adjusted for the application. Registers 0x5F-0x61 configure the PWM frequency for PWM1-PWM3, respectively.
-28-
REV. B
ADT7460
PWM DUTY CYCLE REGISTERS XNOR TREE TEST MODE
Reg. 0x30 PWM1 Duty Cycle = 0xFF (100% Default) Reg. 0x31 PWM2 Duty Cycle = 0xFF (100% Default) Reg. 0x32 PWM3 Duty Cycle = 0xFF (100% Default) By reading the PWMx current duty cycle registers, users can keep track of the current duty cycle on each PWM output, even when the fans are running in automatic fan speed control mode or acoustic enhancement mode.
The ADT7460 includes an XNOR tree test mode. This mode is useful for in-circuit test equipment at board-level testing. By applying stimulus to the pins included in the XNOR tree, it is possible to detect opens or shorts on the system board. Figure 39 shows the signals that are exercised in the XNOR tree test mode.
TACH1 TACH2
TACH3
TACH4
PWM2
PWM3
PWM1/XTO
VARY PWM DUTY CYCLE WITH 8-BIT RESOLUTION
Figure 39. XNOR Tree Test
The XNOR tree test is invoked by setting Bit 0 (XEN) of the XNOR tree test enable register (Reg. 0x6F).
POWER-ON DEFAULT
Figure 38. Control PWM Duty Cycle Manually with a Resolution of 0.39%
OPERATING FROM 3.3 V STANDBY
The ADT7460 has been specifically designed to operate from a 3.3 V STBY supply. In computers that support S3 and S5 states, the core voltage of the processor will be lowered in these states. If using the dynamic TMIN mode, lowering the core voltage of the processor would change the CPU temperature and change the dynamics of the system under dynamic TMIN control. Likewise, when monitoring THERM, the THERM timer should be disabled during these states.
The ADT7460 does not monitor temperature and fan speed by default on power-up. Monitoring of temperature and fan speed is enabled by setting the start bit in configuration Register 1 (Bit 0, Address 0x40) to 1. The fans will run at full speed on power-up. This is because the BHVR bits (Bits <7:5>) in the PWMx configuration registers are set to 100 (fans run full speed) by default.
REV. B
-29-
ADT7460
Table IV. ADT7460 Registers
Address 0x20 0x22 0x25 0x26 0x27 0x28 0x29 0x2A 0x2B 0x2C 0x2D 0x2E 0x2F 0x30 0x31 0x32 0x33 0x34 0x35 0x36 0x37 0x3D 0x3E 0x3F 0x40 0x41 0x42 0x44 0x45 0x48 0x49 0x4E 0x4F 0x50 0x51 0x52 0x53 0x54 0x55 0x56 0x57 0x58 0x59 0x5A 0x5B R/W R R R R R R R R R R R R R R/W R/W R/W R/W R/W R/W R/W R/W R R R R/W R R R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W Description 2.5 V Reading VCC Reading Remote 1 Temperature Local Temperature Remote 2 Temperature TACH1 Low Byte TACH1 High Byte TACH2 Low Byte TACH2 High Byte TACH3 Low Byte TACH3 High Byte TACH4 Low Byte TACH4 High Byte PWM1 Current Duty Cycle PWM2 Current Duty Cycle PWM3 Current Duty Cycle Remote 1 Operating Point Local Temp Operating Point Remote 2 Operating Point Dynamic TMIN Control Reg. 1 Dynamic TMIN Control Reg. 2 Device ID Register Company ID Number Revision Number Configuration Register 1 Interrupt Status Register 1 Interrupt Status Register 2 2.5 V Low Limit 2.5 V High Limit VCC Low Limit VCC High Limit Remote 1 Temp Low Limit Remote 1 Temp High Limit Local Temp Low Limit Local Temp High Limit Remote 2 Temp Low Limit Remote 2 Temp High Limit TACH1 Minimum Low Byte TACH1 Minimum High Byte TACH2 Minimum Low Byte TACH2 Minimum High Byte TACH3 Minimum Low Byte TACH3 Minimum High Byte TACH4 Minimum Low Byte TACH4 Minimum High Byte Bit 7 9 9 9 9 9 7 15 7 15 7 15 7 15 7 7 7 7 7 7 R2T CYR2 7 7 VER VCC OOL D2 7 7 7 7 7 7 7 7 7 7 7 15 7 15 7 15 7 15 Bit 6 8 8 8 8 8 6 14 6 14 6 14 6 14 6 6 6 6 6 6 LT CYR2 6 6 VER TODIS R2T D1 6 6 6 6 6 6 6 6 6 6 6 14 6 14 6 14 6 14 Bit 5 Bit 4 Bit 3 Bit 2 4 4 4 4 4 2 10 2 10 2 10 2 10 2 2 2 2 2 2 PHTR1 CYR1 2 2 STP RDY VCC FAN1 2 2 2 2 2 2 2 2 2 2 2 10 2 10 2 10 2 10 Bit 1 3 3 3 3 3 1 9 1 9 1 9 1 9 1 1 1 1 1 1 VCCRES CYR1 1 1 STP LOCK RES OVT 1 1 1 1 1 1 1 1 1 1 1 9 1 9 1 9 1 9 Bit 0 2 2 2 2 2 0 8 0 8 0 8 0 8 0 0 0 0 0 0 CYR2 CYR1 0 0 STP STRT 2.5V RES 0 0 0 0 0 0 0 0 0 0 0 8 0 8 0 8 0 8 Default 0x00 0x00 0x80 0x80 0x80 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0xFF 0xFF 0xFF 0x64 0x64 0x64 0x00 0x00 0x27 0x41 0x62 0x00 0x00 0x00 0x00 0xFF 0x00 0xFF 0x81 0x7F 0x81 0x7F 0x81 0x7F 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF Lockable?
7 6 5 7 6 5 7 6 5 7 6 5 7 6 5 5 4 3 13 12 11 5 4 3 13 12 11 5 4 3 13 12 11 5 4 3 13 12 11 5 4 3 5 4 3 5 4 3 5 4 3 5 4 3 5 4 3 R1T PHTR2 PHTL CYL CYL CYL 5 4 3 5 4 3 VER VER STP FSPDIS RES FSPD LT R1T RES 5 FAN3 FAN2 5 4 3 5 4 3 5 4 3 5 4 3 5 4 3 5 4 3 5 4 3 5 4 3 5 4 3 5 4 3 5 4 3 13 12 11 5 4 3 13 12 11 5 4 3 13 12 11 5 4 3 13 12 11
YES YES YES YES YES
YES
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REV. B
ADT7460
Table IV. ADT7460 Registers (continued)
Address 0x5C 0x5D 0x5E 0x5F 0x60 0x61 0x62 0x63 0x64 0x65 0x66 0x67 0x68 0x69 0x6A 0x6B 0x6C 0x6D 0x6E 0x6F 0x70 0x71 0x72 0x73 0x74 0x75 0x76 0x77 0x78 0x79 0x7A 0x7B 0x7D 0x7E 0x7F R/W Description R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R R/W R/W R/W R R PWM1 Configuration Register PWM2 Configuration Register PWM3 Configuration Register Remote 1 TRANGE/PWM 1 Freq. Local TRANGE/PWM 2 Freq Remote 2 TRANGE/PWM 3 Freq. Enhance Acoustics Reg. 1 Enhance Acoustics Reg. 2 PWM1 Min Duty Cycle PWM2 Min Duty Cycle PWM3 Min Duty Cycle Remote 1 Temp TMIN Local Temp TMIN Remote 2 Temp TMIN Remote 1 THERM Limit Local THERM Limit Remote 2 THERM Limit Remote 1 Local Hysteresis Remote 2 Temp Hysteresis XNOR Tree Test Enable Remote 1 Temperature Offset Local Temperature Offset Remote 2 Temperature Offset Configuration Register 2 Interrupt Mask Register 1 Interrupt Mask Register 2 Extended Resolution 1 Extended Resolution 2 Configuration Register 3 THERM Status Register THERM Limit Register Fan Pulses per Revolution Configuration Register 4 Test Register 1 Test Register 2 Bit 7 BHVR BHVR BHVR RANGE RANGE RANGE MIN3 EN2 7 7 7 7 7 7 7 7 7 HYSR1 HYSR2 RES 7 7 7 SHDN OOL D2 RES TDM2 DC4 TMR LIMT FAN4 RES Bit 6 BHVR BHVR BHVR RANGE RANGE RANGE MIN2 ACOU2 6 6 6 6 6 6 6 6 6 HYSR1 HYSR2 RES 6 6 6 CONV R2T D1 RES TDM2 DC3 TMR LIMT FAN4 RES Bit 5 BHVR BHVR BHVR RANGE RANGE RANGE MIN1 ACOU2 5 5 5 5 5 5 5 5 5 HYSR1 HYSR2 RES 5 5 5 ATTN LT F4P VCC LTMP DC2 TMR Bit 4 INV INV INV RANGE RANGE RANGE SYNC ACOU2 4 4 4 4 4 4 4 4 4 HYSR1 HYSR2 RES 4 4 4 AVG R1T FAN3 VCC LTMP DC1 TMR Bit 3 SLOW SLOW SLOW THRM THRM THRM EN1 EN3 3 3 3 3 3 3 3 3 3 HYSL RES RES 3 3 3 AIN4 RES FAN2 RES TDM1 FAST TMR Bit 2 SPIN SPIN SPIN FREQ FREQ FREQ ACOU ACOU3 2 2 2 2 2 2 2 2 2 HYSL RES RES 2 2 2 AIN3 VCC FAN1 RES TDM1 BOOST TMR Bit 1 SPIN SPIN SPIN FREQ FREQ FREQ ACOU ACOU3 1 1 1 1 1 1 1 1 1 HYSL RES RES 1 1 1 AIN2 RES OVT 2.5V RES THERM ENABLE TMR Bit 0 Default Lockable? YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES
SPIN 0x62 SPIN 0x62 SPIN 0x62 FREQ 0xC4 FREQ 0xC4 FREQ 0xC4 ACOU 0x00 ACOU3 0x00 0 0x80 0 0x80 0 0x80 0 0x5A 0 0x5A 0 0x5A 0 0x64 0 0x64 0 0x64 HYSL 0x44 RES 0x40 XEN 0x00 0 0x00 0 0x00 0 0x00 AIN1 0x00 2.5V 0x00 RES 0x00 2.5V 0x00 RES 0x00 ALERT 0x00 ASRT/ TMR LIMT FAN1 AL2.5V 0x00 0x00 0x55 0x00 0x00 0x00
YES
LIMT LIMT LIMT LIMT LIMT FAN3 FAN3 FAN2 FAN2 FAN1 RES RES AINL AINL RES DO NOT WRITE TO THESE REGISTERS DO NOT WRITE TO THESE REGISTERS
YES YES YES
REV. B
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ADT7460
Table V. Voltage Reading Registers (Power-On Default = 0x00)
Register Address 0x20 0x22
R/W Read-Only Read-Only
Description 2.5 V Reading (8 MSBs of reading) VCC Reading: Measures VCC through the VCC pin (8 MSBs of Reading)
These voltage readings are in twos complement format. If the extended resolution bits of these readings are also being read, the extended resolution registers (Reg. 0x76, 0x77) should be read first. Once the extended resolution registers get read, the associated MSB reading registers get frozen until read. Both the extended resolution registers and the MSB registers get frozen.
Table VI. Temperature Reading Registers (Power-On Default = 0x80)
Register Address 0x25 0x26 0x27
R/W Read-Only Read-Only Read-Only
Description Remote 1 Temperature Reading* (8 MSBs of Reading) Local Temperature Reading (8 MSBs of Reading) Remote 2 Temperature Reading* (8 MSBs of Reading)
These temperature readings are in twos complement format. *Note that a reading of 0x80 in a temperature reading register indicates a diode fault (open or short) on that channel. If the extended resolution bits of these readings are also being read, the extended resolution registers (Reg. 0x76, 0x77) should be read first. Once the extended resolution registers get read, all associated MSB reading registers get frozen until read. Both the extended resolution registers and the MSB registers get frozen.
Table VII. Fan Tachometer Reading Registers (Power-On Default = 0x00)
Register Address 0x28 0x29 0x2A 0x2B 0x2C 0x2D 0x2E 0x2F
R/W Read-Only Read-Only Read-Only Read-Only Read-Only Read-Only Read-Only Read-Only
Description TACH1 Low Byte TACH1 High Byte TACH2 Low Byte TACH2 High Byte TACH3 Low Byte TACH3 High Byte TACH4 Low Byte TACH4 High Byte
These registers count the number of 11.11 s periods (based on an internal 90 kHz clock) that occur between a number of consecutive fan TACH pulses (default = 2). The number of TACH pulses used to count can be changed using the fan pulses per revolution register (Reg. 0x7B). This allows the fan speed to be accurately measured. Since a valid fan tachometer reading requires that two bytes are read, the low byte MUST be read first. Both the low and high bytes are then frozen until read. At power-on, these registers contain 0x0000 until such time as the first valid fan TACH measurement is read in to these registers. This prevents false interrupts from occurring while the fans are spinning up.
A count of 0xFFFF indicates that a fan is:
1. Stalled or Blocked (object jamming the fan) 2. Failed (internal circuitry destroyed) 3. Not Populated (The ADT7460 expects to see a fan connected to each TACH. If a fan is not connected to that TACH, its TACH minimum high and low byte should be set to 0xFFFF.) 4. Alternate Function, e.g., TACH4 reconfigured as THERM pin 5. 2-Wire Instead of 3-Wire Fan
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REV. B
ADT7460
Table VIII. Current PWM Duty Cycle Registers (Power-On Default = 0xFF)
Register Address 0x30 0x31 0x32
R/W Read/Write Read/Write Read/Write
Description PWM1 Current Duty Cycle (0% to 100% Duty Cycle = 0x00 to 0xFF) PWM2 Current Duty Cycle (0% to 100% Duty Cycle = 0x00 to 0xFF) PWM3 Current Duty Cycle (0% to 100% Duty Cycle = 0x00 to 0xFF)
These registers reflect the PWM duty cycle driving each fan at any given time. When in automatic fan speed control mode, the ADT7460 reports the PWM duty cycles back through these registers. The PWM duty cycle values will vary according to temperature in automatic fan speed control mode. During fan startup, these registers report back 0x00. In software mode, the PWM duty cycle outputs can be set to any duty cycle value by writing to these registers.
Table IX. Operating Point Registers (Power-On Default = 0x64)
Register Address 0x33 0x34 0x35
R/W* Read/Write Read/Write Read/Write
Description Remote 1 Operating Point Register (Default = 100 C) Local Temp Operating Point Register (Default = 100 C) Remote 2 Operating Point Register (Default = 100 C)
These registers set the target operating point for each temperature channel when the dynamic T MIN control feature is enabled. The fans being controlled will be adjusted to maintain temperature about an operating point. *These registers become read-only when the Configuration Register 1 lock bit is set to 1. Any subsequent attempts to write to these registers will fail.
REV. B
-33-
ADT7460
Table X. Register 0x36 - Dynamic TMIN Control Register 1 (Power-On Default = 0x00)
Bit <0>
Name CYR2
R/W* Read/Write
Description MSB of 3-Bit Remote 2 Cycle Value. The other two bits of the code reside in Dynamic TMIN Control Register 2 (Reg. 0x37). These three bits define the delay time between making subsequent TMIN adjustments in the control loop, in terms of number of monitoring cycles. The system will have associated thermal time constants that need to be found to optimize the response of fans and the control loop. Reserved for future use. PHTR1 = 1 copies the Remote 1 current temperature to the Remote 1 operating point register if THERM gets asserted. The operating point will contain the temperature at which THERM is asserted. This allows the system to run as quietly as possible without system performance being affected. PHTR1 = 0 ignores any THERM assertions on the THERM pin. The Remote 1 operating point register will reflect its programmed value. PHTL = 1 copies the local channel's current temperature to the local operating point register if THERM gets asserted. The operating point will contain the temperature at which THERM is asserted. This allows the system to run as quietly as possible without system performance being affected. PHTL = 0 ignores any THERM assertions on the THERM pin. The local temp operating point register will reflect its programmed value. PHTR2 = 1 copies the Remote 2 current temperature to the Remote 2 operating point register if THERM gets asserted. The operating point will contain the temperature at which THERM is asserted. This allows the system to run as quietly as possible without system performance being affected. PHTR2 = 0 ignores any THERM assertions on the THERM pin. The Remote 2 operating point register will reflect its programmed value. R1T = 1 enables dynamic TMIN control on the Remote 1 temperature channel. The chosen TMIN value will be dynamically adjusted based on the current temperature, operating point, and high and low limits for this zone. R1T = 0 disables dynamic TMIN control. The TMIN value chosen will not be adjusted and the channel will behave as described in the Automatic Fan Control section. LT = 1 enables dynamic TMIN control on the local temperature channel. The chosen TMIN value will be dynamically adjusted based on the current temperature, operating point, and high and low limits for this zone. LT = 0 disables dynamic TMIN control. The TMIN value chosen will not be adjusted and the channel will behave as described in the Automatic Fan Control section. R2T = 1 enables dynamic TMIN control on the Remote 2 temperature channel. The chosen TMIN value will be dynamically adjusted based on the current temperature, operating point, and high and low limits for this zone. R2T = 0 disables dynamic TMIN control. The TMIN value chosen will not be adjusted and the channel will behave as described in the Automatic Fan Control section.
<1> <2>
Reserved PHTR1
Read-Only Read/Write
<3>
PHTL
Read/Write
<4>
PHTR2
Read/Write
<5>
R1T
Read/Write
<6>
LT
Read/Write
<7>
R2T
Read/Write
*This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any subsequent attempts to write to this register will fail.
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REV. B
ADT7460
Table XI. Register 0x37 - Dynamic TMIN Control Register 2 (Power-On Default = 0x00)
Bit
Name
R/W* Read/Write
Description 3-Bit Remote 1 Cycle Value. These three bits define the delay time between making subsequent TMIN adjustments in the control loop for the Remote 1 channel, in terms of number of monitoring cycles. The system will have associated thermal time constants that need to be found to optimize the response of fans and the control loop. Bits 000 001 010 011 100 101 110 111 Decrease Cycle 4 Cycles (0.5 s) 8 Cycles (1 s) 16 Cycles (2 s) 32 Cycles (4 s) 64 Cycles (8 s) 128 Cycles (16 s) 256 Cycles (32 s) 512 Cycles (64 s) Increase Cycle 8 Cycles (1 s) 16 Cycles (2 s) 32 Cycles (4 s) 64 Cycles (8 s) 128 Cycles (16 s) 256 Cycles (32 s) 512 Cycles (64 s) 1024 Cycles (128 s)
<2:0> CYR1
<5:3>
CYL
Read/Write
3-Bit Local Temp Cycle Value. These three bits define the delay time between making subsequent TMIN adjustments in the control loop for local temperature channel, in terms of number of monitoring cycles. The system will have associated thermal time constants that need to be found to optimize the response of fans and the control loop. Bits 000 001 010 011 100 101 110 111 Decrease Cycle 4 Cycles (0.5 s) 8 Cycles (1 s) 16 Cycles (2 s) 32 Cycles (4 s) 64 Cycles (8 s) 128 Cycles (16 s) 256 Cycles (32 s) 512 Cycles (64 s) Increase Cycle 8 Cycles (1 s) 16 Cycles (2 s) 32 Cycles (4 s) 64 Cycles (8 s) 128 Cycles (16 s) 256 Cycles (32 s) 512 Cycles (64 s) 1024 Cycles (128 s)
<7:6> CYR2
Read/Write
2 LSBs of 3-Bit Remote 2 Cycle Value. The MSB of the 3-bit code resides in Dynamic TMIN Control Register 1 (Reg. 0x36). These three bits define the delay time between making subsequent TMIN adjustments in the control loop for the Remote 2 channel, in terms of number of monitoring cycles. The system will have associated thermal time constants that need to be found to optimize the response of fans and the control loop. Bits 000 001 010 011 100 101 110 111 Decrease Cycle 4 Cycles (0.5 s) 8 Cycles (1 s) 16 Cycles (2 s) 32 Cycles (4 s) 64 Cycles (8 s) 128 Cycles (16 s) 256 Cycles (32 s) 512 Cycles (64 s) Increase Cycle 8 Cycles (1 s) 16 Cycles (2 s) 32 Cycles (4 s) 64 Cycles (8 s) 128 Cycles (16 s) 256 Cycles (32 s) 512 Cycles (64 s) 1024 Cycles (128 s)
*This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any subsequent attempts to write to this register will fail.
REV. B
-35-
ADT7460
Table XII. Register 0x40 - Configuration Register 1 (Power-On Default = 0x00)
Bit <0>
Name STRT
R/W Read/Write
Description Logic 1 enables monitoring and PWM control outputs based on the limit settings programmed. Logic 0 disables monitoring and PWM control based on the default power-up limit settings. Note that the limit values programmed are preserved even if a Logic 0 is written to this bit and the default settings are enabled. This bit becomes read-only and cannot be changed once Bit 1 (lock bit) has been written. All limit registers should be programmed by BIOS before setting this bit to 1. (Lockable.) Logic 1 locks all limit values to their current settings. Once this bit is set, all lockable registers become read-only and cannot be modified until the ADT7460 is powered down and powered up again. This prevents rogue programs such as viruses from modifying critical system limit settings. (Lockable.) This bit gets set to 1 by the ADT7460 to indicate that the device is fully powered-up and ready to begin systems monitoring. When set to 1, this runs all fans at full speed. Power-on default = 0. This bit does not get locked at any time. Reserved for future use. Logic 1 disables fan spin-up for two TACH pulses. Instead, the PWM outputs will go high for the entire fan spin-up timeout selected. When this bit is set to 1, the SMBus timeout feature is disabled. This allows the ADT7460 to be used with SMBus controllers that cannot handle SMBus timeouts. (Lockable.) When this bit is set to 1, the ADT7460 rescales its VCC pin to measure a 5 V supply. If this bit is 0, the ADT7460 measures VCC as a 3.3 V supply. (Lockable.)
<1>
LOCK
Write Once
<2> <3> <4> <5> <6>
RDY FSPD RES FSPDIS TODIS
Read-Only Read/Write Read-Only Read/Write Read/Write
<7>
VCC
Read/Write
Table XIII. Register 0x41 - Interrupt Status Register 1 (Power-On Default = 0x00)
Bit <0> <1> <2> <3> <4> <5> <6> <7>
Name 2.5V RES VCC RES R1T LT R2T OOL
R/W Read-Only Read-Only Read-Only Read-Only Read-Only Read-Only Read-Only Read-Only
Description A one indicates the 2.5 V high or low limit has been exceeded. This bit gets cleared on a read of the status register only if the error condition has subsided. Reserved for future use. A one indicates the VCC high or low limit has been exceeded. This bit gets cleared on a read of the status register only if the error condition has subsided. Reserved for future use. A one indicates the Remote 1 low or high temperature limit has been exceeded. This bit gets cleared on a read of the Status Register only if the error condition has subsided. A one indicates the local low or high temperature limit has been exceeded. This bit gets cleared on a read of the Status Register only if the error condition has subsided. A one indicates the Remote 2 low or high temperature limit has been exceeded. This bit gets cleared on a read of the Status Register only if the error condition has subsided. A one indicates that an out-of-limit event has been latched in Status Register 2. This bit is a logical OR of all status bits in Status Register 2. Software can test this bit in isolation to determine whether any of the voltage, temperature, or fan speed readings represented by Status Register 2 are out-of-limit. This saves the need to read Status Register 2 every interrupt or polling cycle.
-36-
REV. B
ADT7460
Table XIV. Register 0x42 - Interrupt Status Register 2 (Power-On Default = 0x00)
Bit <0> <1>
Name RES OVT
R/W Read-Only Read-Only
Description Reserved for future use. A one indicates that one of the THERM overtemperature limits has been exceeded. This bit gets cleared on a read of the status register when the temperature drops below THERM - THYST. A one indicates that Fan 1 has dropped below minimum speed or has stalled. This bit does NOT get set when the PWM1 output is off. A one indicates that Fan 2 has dropped below minimum speed or has stalled. This bit does NOT get set when the PWM2 output is off. A one indicates that Fan 3 has dropped below minimum speed or has stalled. This bit does NOT get set when the PWM3 output is off. A one indicates that Fan 4 has dropped below minimum speed or has stalled. This bit does NOT get set when the PWM3 output is off. If Pin 9 is configured as the THERM timer input for THERM monitoring, then this bit gets set when the THERM assertion time exceeds the limit programmed in the THERM Limit Register (Reg. 0x7A). A one indicates either an open or short circuit on the Thermal Diode 1 inputs. A one indicates either an open or short circuit on the Thermal Diode 2 inputs.
Table XV. Voltage Limit Registers
<2> <3> <4> <5>
FAN1 FAN2 FAN3 F4P
Read-Only Read-Only Read-Only Read-Only Read-Only
<6> <7>
D1 D2
Read-Only Read-Only
Register Address 0x44 0x45 0x48 0x49
R/W Read/Write Read/Write Read/Write Read/Write
Description 2.5 V Low Limit 2.5 V High Limit VCC Low Limit VCC High Limit
Power-On Default 0x00 0xFF 0x00 0xFF
Setting the Configuration Register 1 lock bit has no effect on these registers. High Limits: An interrupt is generated when a value exceeds its high limit (> comparison). Low Limits: An interrupt is generated when a value is equal to or below its low limit ( comparison).
Table XVI. Temperature Limit Registers
Register Address 0x4E 0x4F 0x50 0x51 0x52 0x53
R/W Read/Write Read/Write Read/Write Read/Write Read/Write Read/Write
Description Remote 1 Temp Low Limit Remote 1 Temp High Limit Local Temp Low Limit Local Temp High Limit Remote 2 Temp Low Limit Remote 2 Temp High Limit
Power-On Default 0x81 0x7F 0x81 0x7F 0x81 0x7F
Exceeding any of these temperature limits by 1 C will cause the appropriate status bit to be set in the interrupt status register. Setting the Configuration Register 1 lock bit has no effect on these registers. High Limits: An interrupt is generated when a value exceeds its high limit (> comparison). Low Limits: An interrupt is generated when a value is equal to or below its low limit ( comparison).
REV. B
-37-
ADT7460
Table XVII. Fan Tachometer Limit Registers
Register Address 0x54 0x55 0x56 0x57 0x58 0x59 0x5A 0x5B
R/W Read/Write Read/Write Read/Write Read/Write Read/Write Read/Write Read/Write Read/Write
Description TACH1 Minimum Low Byte TACH1 Minimum High Byte TACH2 Minimum Low Byte TACH2 Minimum High Byte TACH3 Minimum Low Byte TACH3 Minimum High Byte TACH4 Minimum Low Byte TACH4 Minimum High Byte
Power-On Default 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
Exceeding any of the TACH limit registers by 1 indicates that the fan is running too slowly or has stalled. The appropriate status bit will be set in Interrupt Status Register 2 to indicate the fan failure. Setting the Configuration Register 1 lock bit has no effect on these registers.
Table XVIII. PWM Configuration Registers
Register Address 0x5C 0x5D 0x5E Bit <2:0> Name SPIN
R/W* Read/Write Read/Write Read/Write R/W Read/Write
Description PWM1 Configuration PWM2 Configuration PWM3 Configuration Description
Power-On Default 0x62 0x62 0x62
These bits control the start-up timeout for PWMx. The PWM output stays high until two valid TACH rising edges are seen from the fan. If there is not a valid TACH signal during the fan TACH measurement directly after the fan start-up timeout period, then the TACH measurement will read 0xFFFF and Status Register 2 reflects the fan fault. If the TACH minimum high and low byte contains 0xFFFF or 0x0000, then the Status Register 2 bit will not get set, even if the fan has not started. 000 = No Start-Up timeout 001 = 100 ms 010 = 250 ms (Default) 011 = 400 ms 100 = 667 ms 101 = 1 s 110 = 2 s 111 = 4 s SLOW = 1 makes the ramp rates for acoustic enhancement four times longer. This bit inverts the PWM output. The default is 0, which corresponds to a logic high output for 100% duty cycle. Setting this bit to 1 inverts the PWM output, so 100% duty cycle corresponds to a logic low output. These bits assign each fan to a particular temperature sensor for localized cooling. 000 = Remote 1 temp controls PWMx (automatic fan control mode). 001 = Local temp controls PWMx (automatic fan control mode). 010 = Remote 2 temp controls PWMx (automatic fan control mode). 011 = PWMx runs full speed (default). 100 = PWMx is disabled. 101 = Fastest Speed Calculated by Local and Remote 2 Temp Control PWMx 110 = Fastest Speed Calculated by all three Temp Channels Control PWMx 111 = Manual Mode. PWM duty cycle registers (Reg. 0x30-0x32) become writable.
<3> <4>
SLOW INV
Read/Write Read/Write
<7:5>
BHVR
Read/Write
*These registers become read-only when the Configuration Register 1 Lock bit is set to 1. Any subsequent attempts to write to these registers will fail.
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REV. B
ADT7460
Table XIX. TEMP TRANGE/PWM Frequency Registers
Register Address 0x5F 0x60 0x61 Bit <2:0> Name FREQ
R/W* Read/Write Read/Write Read/Write R/W Read/Write
Description Remote 1 TRANGE/PWM1 Frequency Local Temp TRANGE/PWM2 Frequency Remote 2 TRANGE/PWM3 Frequency Description These bits control the PWMx frequency. 000 = 11.0 Hz 001 = 14.7 Hz 010 = 22.1 Hz 011 = 29.4 Hz 100 = 35.3 Hz (Default) 101 = 44.1 Hz 110 = 58.8 Hz 111 = 88.2 Hz
Power-On Default 0xC4 0xC4 0xC4
<3>
THRM
Read/Write
THRM = 1 causes the THERM pin (Pin 9) to assert low as an output when this temperature channel's THERM limit has been exceeded by 0.25 C. The THERM pin will remain asserted until the temperature is equal to or below the THERM limit. The minimum time that THERM asserts for is one monitoring cycle. This allows clock modulation of devices that incorporate this feature. THRM = 0 makes the THERM pin act as an input only, e.g., for Pentium 4 PROCHOT monitoring, when Pin 9 is configured as THERM. These bits determine the PWM duty cycle versus temperature slope for automatic fan control. 0000 = 2 C 0001 = 2.5 C 0010 = 3.33 C 0011 = 4 C 0100 = 5 C 0101 = 6.67 C 0110 = 8 C 0111 = 10 C 1000 = 13.33 C 1001 = 16 C 1010 = 20 C 1011 = 26.67 C 1100 = 32 C (Default) 1101 = 40 C 1110 = 53.33 C 1111 = 80 C
<7:4>
RANGE
Read/Write
*These registers become read-only when the Configuration Register 1 lock bit is set. Any further attempts to write to these registers will have no effect.
REV. B
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ADT7460
Table XX. Register 0x62 - Enhance Acoustics Register 1 (Power-On Default = 0x00)
Bit <2:0>
Name ACOU
R/W* Read/Write
Description These bits select the ramp rate applied to the PWM1 output. Instead of PWM1 jumping instantaneously to its newly calculated speed, PWM1 will ramp gracefully at the rate determined by these bits. This feature enhances the acoustics of the fan being driven by the PWM1 output. Time Slot Increase Time for 33% to 100% 000 = 1 35 s 001 = 2 17.6 s 010 = 3 18 s 011 = 5 7s 100 = 8 4.4 s 101 = 12 3s 110 = 24 1.6 s 111 = 48 0.8 s When this bit is 1, acoustic enhancement is enabled on PWM1 output. SYNC = 1 synchronizes fan speed measurements on TACH2, TACH3, and TACH4 to PWM3. This allows up to three fans to be driven from PWM3 output and their speeds to be measured. SYNC = 0, only TACH3 and TACH4 are synchronized to PWM3 output. When the ADT7460 is in automatic fan control mode, this bit defines whether PWM1 is off (0% duty cycle) or at PWM1 minimum duty cycle when the controlling temperature is below its TMIN - Hysteresis value. 0 = 0% Duty Cycle below TMIN - Hysteresis 1 = PWM1 Minimum Duty Cycle below TMIN - Hysteresis When the ADT7460 is in automatic fan speed control mode, this bit defines whether PWM2 is off (0% duty cycle) or at PWM2 minimum duty cycle when the controlling temperature is below its TMIN - Hysteresis value. 0 = 0% Duty Cycle below TMIN - Hysteresis 1 = PWM2 Minimum Duty Cycle below TMIN - Hysteresis When the ADT7460 is in automatic fan speed control mode, this bit defines whether PWM3 is off (0% duty cycle) or at PWM3 minimum duty cycle when the controlling temperature is below its TMIN - Hysteresis value. 0 = 0% Duty Cycle below TMIN - Hysteresis 1 = PWM3 Minimum Duty Cycle below TMIN - Hysteresis
<3> <4>
EN1 SYNC
Read/Write Read/Write
<5>
MIN1
Read/Write
<6>
MIN2
Read/Write
<7>
MIN3
Read/Write
*This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register will have no effect.
-40-
REV. B
ADT7460
Table XXI. Register 0x63 - Enhance Acoustics Register 2 (Power-On Default = 0x00)
Bit <2:0>
Name ACOU3
R/W* Read/Write
Description These bits select the ramp rate applied to the PWM3 output. Instead of PWM3 jumping instantaneously to its newly calculated speed, PWM3 will ramp gracefully at the rate determined by these bits. This effect enhances the acoustics of the fan being driven by the PWM3 output. Time Slot Increase 000 = 1 001 = 2 010 = 3 011 = 5 100 = 8 101 = 12 110 = 24 111 = 48 Time for 33% to 100% 35 s 17.6 s 1.8 s 7s 4.4 s 3s 1.6 s 0.8 s
<3> <6:4>
EN3 ACOU2
Read/Write Read/Write
When this bit is 1, acoustic enhancement is enabled on PWM3 output. These bits select the ramp rate applied to the PWM2 output. Instead of PWM2 jumping instantaneously to its newly calculated speed, PWM2 will ramp gracefully at the rate determined by these bits. This effect enhances the acoustics of the fans being driven by the PWM2 output. Time Slot Increase 000 = 1 001 = 2 010 = 3 011 = 5 100 = 8 101 = 12 110 = 24 111 = 48 Time for 33% to 100% 35 s 17.6 s 11.8 s 7s 4.4 s 3s 1.6 s 0.8 s
<7>
EN2
Read/Write
When this bit is 1, acoustic enhancement is enabled on PWM2 output.
*This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register will have no effect.
REV. B
-41-
ADT7460
Table XXII. PWM Min Duty Cycle Registers
Register Address 0x64 0x65 0x66 Bit <7:0>
R/W* Read/Write Read/Write Read/Write Read/Write Read/Write
Description PWM1 Min Duty Cycle PWM2 Min Duty Cycle PWM3 Min Duty Cycle Description
Power-On Default 0x80 (50% duty cycle) 0x80 (50% duty cycle) 0x80 (50% duty cycle)
Name PWM Duty Cycle
These bits define the PWMMIN duty cycle for PWMx. 0x00 = 0% Duty Cycle (Fan Off) 0x40 = 25% Duty Cycle 0x80 = 50% Duty Cycle 0xFF = 100% Duty Cycle (Fan Full Speed)
*These registers become read-only when the ADT7460 is in automatic fan control mode.
Table XXIII. TMIN Registers
Register Address 0x67 0x68 0x69
R/W* Read/Write Read/Write Read/Write
Description Remote 1 Temp TMIN Local Temp TMIN Remote 2 Temp TMIN
Power-On Default 0x5A (90 C) 0x5A (90 C) 0x5A (90 C)
These are the TMIN registers for each temperature channel. When the temperature measured exceeds T MIN, the appropriate fan will run at minimum speed and increase with temperature according to T RANGE. *These registers become read-only when the Configuration Register 1 lock bit is set. Any further attempts to write to these registers shall have no effect.
Table XXIV. THERM Limit Registers
Register Address 0x6A 0x6B 0x6C
R/W* Read/Write Read/Write Read/Write
Description Remote 1 THERM Limit Local THERM Limit Remote 2 THERM Limit
Power-On Default 0x64 (100 C) 0x64 (100 C) 0x64 (100 C)
If any temperature measured exceeds its THERM limit, all PWM outputs will drive their fans at 100% duty cycle. This is a fail-safe mechanism incorporated to cool the system in the event of a critical overtemperature. It also ensures some level of cooling in the event that software or hardware locks up. If set to 0x80, this feature is disabled. The PWM output will remain at 100% until the temperature drops below THERM Limit - Hysteresis. If the THERM pin is programmed as an output, then exceeding these limits by 0.25 C can cause the THERM pin to assert low as an output. *These registers become read-only when the Configuration Register 1 Lock bit is set to 1. Any further attempts to write to these registers will have no effect.
Table XXV. Temperature Hysteresis Registers
Register Address 0x6D 0x6E
R/W* Read/Write Read/Write
Description Remote 1 Local Temp Hysteresis Remote 2 Temp Hysteresis
Power-On Default 0x44 0x40
Each 4-bit value controls the amount of temperature hysteresis applied to a particular temperature channel. Once the temperature for that channel falls below its T MIN value, the fan will remain running at PWM MIN duty cycle until the temperature = T MIN - Hysteresis. Up to 15 C of hysteresis may be assigned to any temperature channel. The hysteresis value chosen will also apply to that temperature channel if its THERM limit is exceeded. The PWM output being controlled will go to 100% if the THERM limit is exceeded and will remain at 100% until the temperature drops below THERM - Hysteresis. For acoustic reasons, it is recommended that the hysteresis value not be programmed less than 4 C. Setting the hysteresis value lower than 4 C will cause the fan to switch on and off regularly when the temperature is close to T MIN. *These registers become read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to these registers will have no effect.
-42-
REV. B
ADT7460
Table XXVI. XNOR Tree Test Enable Register
Register Address 0x6F <0> <7:1>
R/W* Read/Write XEN RES
Description XNOR Tree Test Enable
Power-On Default 0x00
If the XEN bit is set to 1, the device enters the XNOR tree test mode. Clearing the bit removes the device from the XNOR Test Mode. Unused. Do not write to these bits.
*This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register will have no effect.
Table XXVII. Remote 1 Temperature Offset Register
Register Address 0x70 <7:0>
R/W* Read/Write Read/Write
Description Remote 1 Temperature Offset
Power-On Default 0x00
Allows a twos complement offset value to be automatically added to or subtracted from the Remote 1 temperature reading. This is to compensate for any inherent system offsets such as PCB trace resistance. LSB value = 0.25C.
*This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register will have no effect.
Table XXVIII. Local Temperature Offset Register
Register Address 0x71 <7:0>
R/W* Read/Write Read/Write
Description Local Temperature Offset
Power-On Default 0x00
Allows a twos complement offset value to be automatically added to or subtracted from the local temperature reading. LSB value = 0.25C.
*This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register will have no effect.
Table XXIX. Remote 2 Temperature Offset Register
Register Address 0x72 <7:0>
R/W* Read/Write Read/Write
Description Remote 2 Temperature Offset
Power-On Default 0x00
Allows a twos complement offset value to be automatically added to or subtracted from the Remote 2 temperature reading. This is to compensate for any inherent system offsets such as PCB trace resistance. LSB value = 0.25C.
*This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register will have no effect.
REV. B
-43-
ADT7460
Table XXX. Register 0x73 - Configuration Register 2 (Power-On Default = 0x00)
Bit 0
Name AIN1
R/W* Read/Write
Description AIN1 = 0, Speed of 3-wire fans measured using the TACH output from the fan. AIN1 = 1, Pin 6 is reconfigured to measure the speed of 2-wire fans using an external sensing resistor and coupling capacitor. AIN voltage threshold is set via Configuration Register 4 (Reg. 0x7D). AIN2 = 0, Speed of 3-wire fans measured using the TACH output from the fan. AIN2 = 1, Pin 7 is reconfigured to measure the speed of 2-wire fans using an external sensing resistor and coupling capacitor. AIN voltage threshold is set via Configuration Register 4 (Reg. 0x7D). AIN3 = 0, Speed of 3-wire fans measured using the TACH output from the fan. AIN3 = 1, Pin 4 is reconfigured to measure the speed of 2-wire fans using an external sensing resistor and coupling capacitor. AIN voltage threshold is set via Configuration Register 4 (Reg. 0x7D). AIN4 = 0, Speed of 3-wire fans measured using the TACH output from the fan. AIN4 = 1, Pin 9 is reconfigured to measure the speed of 2-wire fans using an external sensing resistor and coupling capacitor. AIN voltage threshold is set via Configuration Register 4 (Reg. 0x7D). AVG = 1, Averaging on the temperature and voltage measurements is turned off. This allows measurements on each channel to be made much faster. ATTN = 1, the ADT7460 removes the attenuators from the 2.5 V input. The input can be used for other functions such as connecting up external sensors. CONV = 1, the ADT7460 is put into a single-channel ADC conversion mode. In this mode, the ADT7460 can be made to read continuously from one input only, e.g., Remote 1 temperature. It is also possible to start ADC conversions using an external clock on Pin 6 by setting Bit 2 of Test Register 2 (Reg. 0x7F). This mode could be useful if, for example, users wanted to characterize/profile CPU temperature quickly. The appropriate ADC channel is selected by writing to Bits <7:5> of TACH1 min high byte register (0x55). Bits <7:5> Reg. 0x55 Channel Selected 000 2.5 V 010 VCC (3.3 V) 101 Remote 1 Temp 110 Local Temp 111 Remote 2 Temp SHDN = 1, ADT7460 goes into shutdown mode. All PWM outputs assert low (or high depending on state of INV bit) to switch off all fans. The PWM current duty cycle registers read 0x00 to indicate that the fans are not being driven.
1
AIN2
Read/Write
2
AIN3
Read/Write
3
AIN4
Read/Write
4 5 6
AVG ATTN CONV
Read/Write Read/Write Read/Write
7
SHDN
Read/Write
*This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register will have no effect.
-44-
REV. B
ADT7460
Table XXXI. Register 0x74 - Interrupt Mask Register 1 (Power-On Default <7:0> = 0x00)
Bit 0 1 2 3 4 5 6 7
Name 2.5V RES VCC RES R1T LT R2T OOL
R/W Read/Write Read/Write Read/Write Read/Write Read/Write Read/Write Read/Write Read/Write
Description A one masks SMBALERT for out-of-limit conditions on the 2.5 V channel. Reserved for future use. A one masks SMBALERT for out-of-limit conditions on the VCC channel. Reserved for future use. A one masks SMBALERT for out-of-limit conditions on the Remote 1 temperature channel. A one masks SMBALERT for out-of-limit conditions on the Local temperature channel. A one masks SMBALERT for out-of-limit conditions on the Remote 2 temperature channel. A one masks SMBALERT for any out-of-limit condition in Status Register 2.
Table XXXII. Register 0x75 - Interrupt Mask Register 2 (Power-On Default <7:0> = 0x00)
Bit 0 1 2 3 4 5 6 7
Name RES OVT FAN1 FAN2 FAN3 F4P D1 D2
R/W Read/Write Read-Only Read/Write Read/Write Read/Write Read/Write Read/Write Read/Write
Description Reserved for future use. A one masks SMBALERT for overtemperature THERM conditions. A one masks SMBALERT for a Fan 1 fault. A one masks SMBALERT for a Fan 2 fault. A one masks SMBALERT for a Fan 3 fault. A one masks SMBALERT for a Fan 4 Fault. If the TACH4 pin is being used as the THERM input, this bit masks SMBALERT for a THERM timer event. A one masks SMBALERT for a diode open or short on Remote 1 channel. A one masks SMBALERT for a diode open or short on Remote 2 channel.
Table XXXIII. Register 0x76 - Extended Resolution Register 1
Bit <1:0> <3:2> <5:4> <7:6>
Name 2.5V RES VCC RES
R/W Read-Only Read/Write Read-Only Read/Write
Description 2.5 V LSBs. Holds the 2 LSBs of the 10-bit 2.5 V measurement. Reserved for future use. VCC LSBs. Holds the 2 LSBs of the 10-bit VCC measurement. Reserved for future use.
If this register is read, this register and the registers holding the MSB of each reading are frozen until read.
Table XXXIV. Register 0x77 - Extended Resolution Register 2
Bit <1:0> <3:2> <5:4> <7:6>
Name RES TDM1 LTMP TDM2
R/W Read/Write Read-Only Read-Only Read-Only
Description Reserved for future use. Remote 1 Temperature LSBs. Holds the 2 LSBs of the 10-bit Remote 1 temperature measurement. Local Temperature LSBs. Holds the 2 LSBs of the 10-bit Local temperature measurement. Remote 2 Temperature LSBs. Holds the 2 LSBs of the 10-bit Remote 2 temperature measurement.
If this register is read, this register and the registers holding the MSB of each reading are frozen until read.
REV. B
-45-
ADT7460
Table XXXV. Register 0x78 - Configuration Register 3 (Power-On Default = 0x00)
Bit <0> <1>
Name ALERT THERM ENABLE BOOST FAST DC1 DC2 DC3 DC4
R/W* Read/Write Read/Write
Description ALERT = 1, Pin 5 (PWM2/SMBALERT) is configured as an SMBALERT interrupt output to indicate out-of-limit error conditions. THERM ENABLE = 1 enables THERM monitoring functionality on Pin 9 when it is configured as THERM. When THERM is asserted, fans can be run at full speed (if the BOOST bit is set) or a timer can be triggered to time how long THERM has been asserted for. BOOST = 1, assertion of THERM will cause all fans to run at 100% duty cycle for fail-safe cooling. FAST = 1 enables fast TACH measurements on all channels. This increases the TACH measurement rate from once per second, to once every 250 ms (4 ). DC1 = 1 enables TACH measurements to be continuously made on TACH1. DC2 = 2 enables TACH measurements to be continuously made on TACH2. DC3 = 1 enables TACH measurements to be continuously made on TACH3. DC4 = 1 enables TACH measurements to be continuously made on TACH4.
<2> <3> <4> <5> <6> <7>
Read/Write Read/Write Read/Write Read/Write Read/Write Read/Write
*This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register will have no effect.
Table XXXVI. Register 0x79 - THERM Status Register (Power-On Default = 0x00)
Bit <7:1> <0>
Name TMR ASRT/TMR0
R/W Read-Only Read-Only
Description Times how long THERM input is asserted. These seven bits will read zero until the THERM assertion time exceeds 45.52 ms. Gets set high on the assertion of the THERM input. Cleared on read. If the THERM assertion time exceeds 45.52 ms, this bit gets set and becomes the LSB of the 8-bit TMR reading. This allows THERM assertion times from 45.52 ms to 5.82 s to be reported back with a resolution of 22.76 ms.
Table XXXVII. Register 0x7A - THERM Limit Register (Power-On Default = 0x00)
Bit <7:0>
Name LIMT
R/W Read/Write
Description Sets maximum THERM assertion length allowed before an interrupt is generated. This is an 8-bit limit with a resolution of 22.76 ms allowing THERM assertion limits of 45.52 ms to 5.82 s to be programmed. If the THERM assertion time exceeds this limit, Bit 5 (F4P) of Interrupt Status Register 2 (Reg. 0x42) will be set. If the limit value is 0x00, then an interrupt will be generated immediately on the assertion of the THERM input.
-46-
REV. B
ADT7460
Table XXXVIII. Register 0x7B - Fan Pulses per Revolution Register (Power-On Default = 0x55)
Bit <1:0>
Name FAN1
R/W Read/Write
Description Sets number of pulses to be counted when measuring Fan1 speed. Can be used to determine fan's pulses per revolution for unknown fan type. Pulses Counted 00 = 1 01 = 2 (Default) 10 = 3 11 = 4 Sets number of pulses to be counted when measuring FAN2 speed. Can be used to determine fan's pulses per revolution for unknown fan type. Pulses Counted 00 = 1 01 = 2 (Default) 10 = 3 11 = 4 Sets number of pulses to be counted when measuring FAN3 speed. Can be used to determine fan's pulses per revolution for unknown fan type. Pulses Counted 00 = 1 01 = 2 (Default) 10 = 3 11 = 4 Sets number of pulses to be counted when measuring FAN4 speed. Can be used to determine fan's pulses per revolution for unknown fan type. Pulses Counted 00 = 1 01 = 2 (Default) 10 = 3 11 = 4
<3:2>
FAN2
Read/Write
<5:4>
FAN3
Read/Write
<7:6>
FAN4
Read/Write
Table XXXIX. Register 0x7D - Configuration Register 4 (Power-On Default = 0x00)
Bit <0>
Name AL2.5V
R/W Read/Write
Description AL2.5V = 1, Pin 14 (2.5V/SMBALERT) is configured as an SMBALERT interrupt output to indicate out-of-limit error conditions. AL2.5V = 0, Pin 14 (2.5V/SMBALERT) is configured as a 2.5 V measurement input. Reserved for future use. These two bits define the input threshold for 2-wire fan speed measurements: 00 = 20 mV 01 = 40 mV 10 = 80 mV 11 = 130 mV Reserved for future use.
<1> <3:2>
RES AINL
Read-Only Read/Write
<7:4>
RES
*This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register will have no effect.
REV. B
-47-
ADT7460
Table XL. Register 0x7E - Manufacturer's Test Register 1 (Power On-Default = 0x00)
Bit <7:0>
Name RES
Read/Write Read-Only
Description Manufacturer's Test Register. These bits are reserved for manufacturer's test purposes and should NOT be written to under normal operation.
Table XLI. Register 0x7F - Manufacturer's Test Register 2 (Power-On Default = 0x00)
Bit <7:0>
Name RES
Read/Write Read-Only
Description Manufacturer's Test Register. These bits are reserved for manufacturer's test purposes and should NOT be written to under normal operation.
-48-
REV. B
ADT7460
OUTLINE DIMENSIONS 16-Lead Shrink Small Outline Package [QSOP] (RQ-16)
Dimensions shown in millimeters
0.193 BSC
16
9
0.154 BSC
1 8
0.236 BSC
PIN 1 0.065 0.049 0.069 0.053
0.010 0.025 0.004 BSC COPLANARITY 0.004
0.012 0.008
SEATING PLANE
0.010 0.006
8 0
0.050 0.016
COMPLIANT TO JEDEC STANDARDS MO-137AB
REV. B
-49-
ADT7460 Revision History
Location 9/03--Data Sheet Changed from REV. A to REV. B. Page
Changed XOR Tree Test Mode to XNOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Universal Changes to SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Changes to TPC 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6/03--Data Sheet changed from REV. 0 to REV. A.
Updated ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Updated the SERIAL BUS INTERFACE section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Added the To Assign THERM Functionality to a Pin 9 section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Added the THERM as an Input section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Renamed the Therm Input section to THERM Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Renumbered the figures after Figure 25 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Updated Step 1 in the Configuring the Desired THERM Behavior section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Updated the Fan Speed Control section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Added the POWER-ON DEFAULT section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Updated Table IV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Updated Table XVIII . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Updated Table XX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Updated Table XXXV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Updated OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
-50-
REV. B
-51-
-52-
C03228-0-9/03(B)

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