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19-3344; Rev 0; 8/04
2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller
General Description
The MAX6640 monitors its own temperature and one external diode-connected transistor or the temperatures of two external diode-connected transistors, typically available in CPUs, FPGAs, or GPUs. The 2-wire serial interface accepts standard System Management Bus (SMBus) TM write byte, read byte, send byte, and receive byte commands to read the temperature data and program the alarm thresholds. Temperature data can be read at any time over the SMBus, and three programmable alarm outputs can be used to generate interrupts, throttle signals, or overtemperature shutdown signals. The temperature data is also used by the internal dual PWM fan-speed controller to adjust the speed of up to two cooling fans, thereby minimizing noise when the system is running cool, but providing maximum cooling when power dissipation increases. Speed control is accomplished by tachometer feedback from the fan, so that the speed of the fan is controlled, not just the PWM duty cycle. Accuracy of speed measurement is 4%. The MAX6640 is available in 16-pin QSOP and 16-pin TQFN 5mm x 5mm packages. It operates from 3.0V to 5.5V and consumes just 500A of supply current.
Features
Two Thermal-Diode Inputs Local Temperature Sensor 1C Remote Temperature Accuracy (+60C to +100C) Two PWM Outputs for Fan Drive (Open Drain; can be Pulled Up to +13.5V) Programmable Fan-Control Characteristics Automatic Fan Spin-Up Ensures Fan Start Controlled Rate-of-Change Ensures Unobtrusive Fan-Speed Adjustments 4% Fan-Speed Measurement Accuracy Temperature Monitoring Begins at POR for FailSafe System Protection OT and THERM Outputs for Throttling or Shutdown Measures Temperatures Up to +150C Tiny 5mm x 5mm 16-Pin TQFN and QSOP Packages
MAX6640
Applications
Desktop Computers Notebook Computers Workstations Servers Networking Equipment
SMBus is a trademark of Intel Corp. Typical Application Circuit appears at end of data sheet.
MAX6640ATE MAX6640AEE PART
Ordering Information
OPERATING MEASUREMENT PINPACKAGE RANGE RANGE -40C to +125C -40C to +125C 0C to +150C 16 QSOP 16 TQFN (5mm x 5mm)
0C to +150C
Pin Configurations
TACH1 PWM1 SDA 14
TOP VIEW
PWM1 1 TACH1 2 PWM2 3 TACH2 4 FANFAIL 5 THERM 6 OT 7 VCC 8 16 SCL 15 SDA 14 ALERT PWM2 TACH2 FANFAIL THERM 1 2 3 4
16
15
13
SCL
12
ALERT VCC DXP2 DXN
MAX6640
13 VCC 12 DXP2 11 DXN 10 GND 9 DXP1
MAX6640
11 10
*CONNECT EXPOSED PADDLE TO GND 5 OT 6 VCC 7 GND 8 DXP1
9
QSOP
5mm x 5mm THIN QFN
________________________________________________________________ Maxim Integrated Products
1
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2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller MAX6640
ABSOLUTE MAXIMUM RATINGS
VCC to GND ..............................................................-0.3V to +6V PWM1, PWM2, TACH1, and TACH2 to GND ......-0.3V to +13.5V DXP1 and DXP2 to GND ..........................-0.3V to +(VCC + 0.3V) DXN to GND ..........................................................-0.3V to +0.8V SCL, SDA, THERM, OT, FANFAIL, and ALERT to GND ..............................................-0.3V to +6V SDA, OT, THERM, ALERT, FANFAIL, PWM1, and PWM2 Current .............................-1mA to +50mA DXN Current .......................................................................1mA ESD Protection (all pins, Human Body Model) ..................2000V Continuous Power Dissipation (TA = +70C) 16-Pin QSOP (derated 8.3mW/C above +70C) ....... 667mW 16-Pin TQFN 5mm x 5mm (derated at 33.3mW/C above +70C)................2666.7mW Operating Temperature Range .........................-40C to +125C Junction Temperature ......................................................+150C Storage Temperature Range ............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VCC = +3.0V to +5.5V, TA = 0C to +125C, unless otherwise noted. Typical values are at VCC = +3.3V, TA = +85C.) (Note 1)
PARAMETER Operating Supply Voltage Range Standby Current Operating Current SYMBOL VCC SMB static, sleep mode Interface inactive, ADC active VCC = +3.3V, +60C TA +100C and +60C TR +100C External Temperature Error VCC = +3.3V, +40C TA +100C and 0C TR +145C VCC = +3.3V, 0C TR +145C VCC = +3.3V, +25C TA +100C VCC = +3.3V, 0C TA +125C Supply Sensitivity of Temperature Measurement Temperature Resolution Conversion Time Conversion-Rate Timing Error PWM Frequency Error Tachometer Accuracy Remote-Diode Sourcing Current DXN Source Voltage VCC = 3.135V to 3.345V, +60C TA +85C High level Low level 70 7.0 100 10 0.7 -10 -10 0.2 +0.125 11 125 +10 +10 4 130 13.0 CONDITIONS MIN +3.0 3 0.5 TYP MAX +5.5 10 1 1 2.5 3.8 2 C 4 C/V C Bits ms % % % A V C UNITS V A mA
Internal Temperature Error
2
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2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.0V to +5.5V, TA = 0C to +125C, unless otherwise noted. Typical values are at VCC = +3.3V, TA = +85C.) (Note 1)
PARAMETER DIGITAL INPUTS AND OUTPUTS Output Low Voltage (Sink Current) (OT, ALERT, FANFAIL, THERM, SDA, PWM1, and PWM2) Output High Leakage Current (OT, ALERT, FANFAIL, THERM, SDA, PWM1, and PWM2) Logic-Low Input Voltage (SDA, SCL, THERM, TACH1, TACH2) Logic-High Input Voltage (SDA, SCL, THERM, TACH1, TACH2) Input Leakage Current (SDA, SCL, THERM, TACH1, TACH2) Input Capacitance SMBus TIMING (Note 2) Serial Clock Frequency Clock Low Period Clock High Period Bus Free Time Between Stop and Start Condition SMBus Start Condition Setup Time Start Condition Hold Time Stop Condition Setup Time Data Setup Time Data Hold Time SMBus Fall Time SMBus Rise Time SMBus Timeout fSCL tLOW tHIGH tBUF tSU:STA tHD:STO tSU:STO tSU:DAT tHD:DAT tF tR tTIMEOUT 58 74 90% of SMBCLK to 90% of SMBDATA 10% of SDA to 10% of SCL 90% of SCL to 10% of SDA 10% of SDA to 10% of SCL 10% of SCL to 10% of SDA (Note 4) (Note 3) 10% to 10% 90% to 90% 10 4 4.7 4.7 4.7 4 4 250 300 300 1000 90 100 kHz s s s s s s ns ns ns ns ms CIN VOL ALERT, FANFAIL, THERM, OT SDA ISINK = 6mA PWM1, PWM2, ISINK = 4mA IOH 0.4 0.4 1 A V SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX6640
VIL VCC = 3.3V VCC = 5.5V VIN = VCC or GND 5 2.1 2.6
0.8
V
VIH
V 1 A pF
Note 1: Note 2: Note 3: Note 4:
All parameters tested at a single temperature. Specifications are guaranteed by design. Timing specifications guaranteed by design. The serial interface resets when SCL is low for more than tTIMEOUT. A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SCL's falling edge.
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2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller MAX6640
Typical Operating Characteristics
(VCC = 3.3V, TA = +25C)
STANDBY SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX6640 toc01
OPERATING SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX6640 toc02
REMOTE TEMPERATURE ERROR vs. REMOTE-DIODE TEMPERATURE
MAX6640 toc03
10 9 8 SUPPLY CURRENT (A) 7 6 5 4 3 2 1 0 3.0 3.5 4.0 4.5 5.0
800 700 SUPPLY CURRENT (A) 600 500 400 300 200
2
TEMPERATURE ERROR (C)
1
0
-1 FAIRCHILD 2N3906 -2
5.5
3.0
3.5
4.0
4.5
5.0
5.5
0
25
50
75
100
125
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
TEMPERATURE (C)
LOCAL TEMPERATURE ERROR vs. DIE TEMPERATURE
MAX6640 toc04
REMOTE TEMPERATURE ERROR vs. POWER-SUPPLY NOISE FREQUENCY
MAX6640 toc05
LOCAL TEMPERATURE ERROR vs. POWER-SUPPLY NOISE FREQUENCY
1.5 TEMPERATURE ERROR (C) 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 VIN = 250mVP-P SQUARE WAVE APPLIED TO VCC WITH NO BYPASS CAPACITOR
MAX6640 toc06
1.0 0.5 TEMPERATURE ERROR (C) 0 -0.5 -1.0 -1.5 -2.0 0 25 50 75 100
2.0 1.5 TEMPERATURE ERROR (C) 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0
VIN = 250mVP-P SQUARE WAVE APPLIED TO VCC WITH NO BYPASS CAPACITOR
2.0
125
10
100
1k FREQUENCY (Hz)
10k
100k
1
10
100
1k
10k
100k
TEMPERATURE (C)
FREQUENCY (Hz)
REMOTE TEMPERATURE ERROR vs. COMMON-MODE NOISE FREQUENCY
MAX6640 toc07
REMOTE TEMPERATURE ERROR vs. DIFFERENTIAL NOISE FREQUENCY
1.5 TEMPERATURE ERROR (C) 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 VIN = AC-COUPLED TO DXP VIN = 100mVP-P SQUARE WAVE
MAX6640 toc08
TEMPERATURE ERROR vs. DXP-DXN CAPACITANCE
1.0 TEMPERATURE ERROR (C) 0 -1.0 -2.0 -3.0 -4.0 -5.0 -6.0 0.1 1 10 100
MAX6640 toc09
2.0 1.5 TEMPERATURE ERROR (C) 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0
VIN = AC-COUPLED TO DXP AND DXN VIN = 100mVP-P SQUARE WAVE
2.0
2.0
0.1
1
10
100
1k
10k
100k
10
100
1k FREQUENCY (Hz)
10k
100k
FREQUENCY (Hz)
DXP-GND CAPACITANCE (nF)
4
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2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller MAX6640
Typical Operating Characteristics (continued)
(VCC = 3.3V, TA = +25C)
PWMOUT FREQUENCY vs. DIE TEMPERATURE
MAX6640 toc10
PWMOUT FREQUENCY vs. SUPPLY VOLTAGE
MAX6640 toc11
35
35
PWMOUT FREQUENCY (Hz)
33
PWMOUT FREQUENCY (Hz) -40 -15 10 35 60 85 110
34
34
33
32
32
31
31
30 TEMPERATURE (C)
30 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
Pin Description
PIN TQFN 1, 15 QSOP 3, 1 NAME PWM2, PWM1 TACH2, TACH1 FUNCTION Open-Drain Output to Power Transistor Driving Fan. Connect to the gate of a MOSFET or base of a bipolar transistor. PWM_ requires a pullup resistor. The pullup resistor can be connected to a supply voltage as high as 13.5V, regardless of the MAX6640's supply voltage. Tachometer Inputs. Connect to the tachometer output of the fan. TACH_ requires a pullup resistor. The pullup resistor can be connected to a supply voltage as high as 13.5V, regardless of the MAX6640's supply voltage. Active-Low, Open-Drain Thermal Alarm Output. Typically used for clock throttling. Open circuit when VCC = 0. Active-Low, Open-Drain Overtemperature Output. Typically used for system shutdown or clock throttling. Can be pulled up to 5.5V regardless of VCC. Open circuit when VCC = 0. Power-Supply Input. 3.3V nominal. Bypass VCC to GND with a 0.1F capacitor. Ground. Connect to a clean ground reference. Combined Current Source and A/D Positive Input for Remote Diode. Connect to anode of remote-diodeconnected temperature-sensing transistor. Do not leave floating; connect to DXN if no remote diode is used. Place a 2200pF capacitor between DXP_ and DXN for noise filtering. Connect Cathode of the Remote-Diode-Connected Transistor to DXN Connect to VCC Active-Low, Open-Drain SMBus Alert Output SMBus Serial-Clock Input. Can be pulled up to 5.5V regardless of VCC. Open circuit when VCC = 0. SMBus Serial-Data Input/Output, Open Drain. Can be pulled up to 5.5V regardless of VCC. Open circuit when VCC = 0.
2, 16 3 4 5 6 7 8, 10 9 11 12 13 14
4, 2 5 6 7 8 10 9, 12 11 13 14 16 15
FANFAIL Active-Low, Open-Drain, Fan-Failure Output. Open circuit when VCC = 0. THERM OT VCC GND DXP1, DXP2 DXN VCC ALERT SCL SDA
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2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller MAX6640
Block Diagram
VCC
Detailed Description
The MAX6640 monitors its own temperature and a remote diode-connected transistor or the temperatures of two external diode-connected transistors, which typically reside on the die of a CPU or other integrated circuit. The 2-wire serial interface accepts standard SMBus write byte, read byte, send byte, and receive byte commands to read the temperature data and program the alarm thresholds. Temperature data can be read at any time over the SMBus, and a programmable alarm output can be used to generate interrupts, throttle signals, or overtemperature shutdown signals. The temperature data is also used by the internal dual PWM fan-speed controller to adjust the speed of up to two cooling fans, thereby minimizing noise when the system is running cool, but providing maximum cooling when power dissipation increases. RPM feedback allows the MAX6640 to control the fan's actual speed.
MAX6640
DXP1 DXN DXP2 TEMPERATURE PROCESSING BLOCK PWM GENERATOR BLOCK PWM1 PWM2
OT THERM LOGIC SMBus INTERFACE AND REGISTERS FANFAIL ALERT TACH1 TACH2 GND
SDA SCL
Write Byte Format S ADDRESS 7 bits Slave Address: equivalent to chip-select line of a 3-wire interface Read Byte Format S ADDRESS 7 bits Slave Address: equivalent to chip-select line Send Byte Format S ADDRESS 7 bits WR ACK COMMAND 8 bits Command Byte: sends command with no data, usually used for one-shot command S = Start condition P = Stop condition Shaded = Slave transmission /// = Not acknowledged ACK P WR ACK COMMAND 8 bits Command Byte: selects which register you are reading from ACK S ADDRESS 7 bits Slave Address: repeated due to change in dataflow direction Receive Byte Format S ADDRESS 7 bits RD ACK DATA 8 bits Data Byte: reads data from the register commanded by the last Read Byte or Write Byte transmission; also used for SMBus Alert Response return address /// P RD ACK DATA 8 bits Data Byte: reads from the register set by the command byte /// P WR ACK COMMAND 8 bits Command Byte: selects which register you are writing to ACK DATA 8 bits ACK P 1
Data Byte: data goes into the register set by the command byte (to set thresholds, configuration masks, and sampling rate)
Figure 1. SMBus Protocols 6 _______________________________________________________________________________________
2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller MAX6640
A tLOW B tHIGH C D E F G H I J K L M
SCL
SDA
tSU:STA tHD:STA A = START CONDITION B = MSB OF ADDRESS CLOCKED INTO SLAVE C = LSB OF ADDRESS CLOCKED INTO SLAVE D = R/W BIT CLOCKED INTO SLAVE
tSU:DAT E = SLAVE PULLS SMBDATA LINE LOW F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO SLAVE H = LSB OF DATA CLOCKED INTO SLAVE I = MASTER PULLS DATA LINE LOW J = ACKNOWLEDGE CLOCKED INTO SLAVE K = ACKNOWLEDGE CLOCK PULSE L = STOP CONDITION M = NEW START CONDITION
tSU:STO
tBUF
Figure 2. SMBus Write Timing Diagram
A B C D E F G H I J K L M
tLOW
tHIGH
SCL
SDA tSU:STA tHD:STA tSU:DAT tHD:DAT F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO MASTER H = LSB OF DATA CLOCKED INTO MASTER I = MASTER PULLS DATA LINE LOW
tSU:STO tBUF J = ACKNOWLEDGE CLOCKED INTO SLAVE K = ACKNOWLEDGE CLOCK PULSE L = STOP CONDITION M = NEW START CONDITION
A = START CONDITION B = MSB OF ADDRESS CLOCKED INTO SLAVE C = LSB OF ADDRESS CLOCKED INTO SLAVE D = R/W BIT CLOCKED INTO SLAVE E = SLAVE PULLS SMBDATA LINE LOW
Figure 3. SMBus Read Timing Diagram
SMBus Digital Interface
From a software perspective, the MAX6640 appears as a set of byte-wide registers. This device uses a standard SMBus 2-wire/I2CTM-compatible serial interface to access the internal registers. The MAX6640 employs four standard SMBus protocols: write byte, read byte, send byte, and receive byte (Figures 1, 2, and 3). The shorter receive byte protocol allows quicker transfers, provided that the correct data register was previously selected by a read byte instruction. Use caution with the shorter protocols in multimaster systems, since a second master could overwrite the command byte without informing the first master.
I2C is a trademark of Philips Corp. Purchase of I2C components of Maxim Integrated Products, Inc., or one of its sublicensed Associated Companies, conveys a license under the Philips I2C Patent Rights to use these components in an I2C system, provided that the system conforms to the I2C Standard Specification as defined by Philips.
Table 3 details the register addresses and functions, whether they can be read or written to, and the poweron reset (POR) state. See Tables 4-8 for all other register functions and the Register Descriptions section.
Temperature Reading
Temperature data can be read from registers 00h and 01h. The temperature data format for these registers is 8 bits, with the LSB representing 1C (Table 1) and the MSB representing +128C. The MSB is transmitted first. Three additional temperature bits provide resolution down to 0.125C and are in the channel 1 extended temperature (05h) and channel 2 extended temperature (06h) registers. All values below 0C clip to 00h. The MAX6640 employs a register lock mechanism to avoid getting temperature results from the temperature register and the extended temperature register sampled at two different time points. Reading the extended register stops the MAX6640 from updating the temperature register for at least 0.25s, unless there is a tem7
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2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller MAX6640
Table 1. Temperature Data Byte Format
TEMP (C) 241 240 126 25 1.50 0.00 TEMP (C) +241 +240 +126 +25 1 0 DIGITAL OUTPUT 1111 0001 1111 0000 0111 1110 0001 1001 0000 0001 0000 0000
temperature channel. The status bit and the ALERT output clear by reading the ALERT status register. If the ALERT status bit is cleared, but the temperature still exceeds the ALERT temperature threshold, ALERT reasserts on the next conversion, and the status bit sets again. A successful alert response protocol clears ALERT, but does not affect the ALERT status bit.
TACH1 and TACH2 Inputs
To measure the fan speed, the MAX6640 has two tachometers. Each tachometer has an accurate internal clock to count the time elapsed in one revolution. Therefore, it is counting the time between two tachometer pulses for a fan with four poles. When the PWM signal is used to directly modulate the fan's power supply, the PWM frequency is normally in the 20Hz to 100Hz range. In this case, the time required for one revolution may be longer than the PWM on-time. For this reason, the PWM pulses are periodically stretched to allow tachometer measurement over a full revolution. Turn off pulse stretching by setting bit 5 of register 13h or register 17h when using a 4-wire fan. The tachometer count is inversely proportional to the fan's RPM. The tachometer count data is stored in register 20h (for TACH1) and register 21h (for TACH2). Reading a value of 255 from the TACH count register means the fan's RPM is zero or too slow for the range. Reading a value of zero in the TACH count register means the fan's RPM is higher than the range selected. Table 2 shows the fan's available RPM ranges. Use registers 10h or 14h to select the appropriate RPM range for the fan being used.
perature register read before the scheduled update. This allows enough time to read the main register before it is updated, thereby preventing reading the temperature register data from one conversion and the extended temperature register data from a different conversion. The MAX6640 measures the temperature at a fixed rate of 4Hz immediately after it is powered on. Setting bit 7 of the configuration register (04h) shuts down the temperature measurement cycle.
OT Output
When a measured temperature exceeds the corresponding OT temperature threshold and OT is not masked, the associated OT status register bit sets and the OT output asserts. If OT for the respective channel is masked, the OT status register sets, but the OT output does not assert. To deassert the OT output and the associated status register bit, either the measured temperature must fall at least 5C below the trip threshold or the trip threshold must be increased to at least 5C above the current measured temperature.
FANFAIL
The FANFAIL output asserts to indicate that one of the fans has failed or is spinning slower than the required speed. The MAX6640 detects fan fault depending on the fan control mode. In PWM mode, the MAX6640 produces a square wave with a duty cycle set by the value written to the duty-cycle registers (26h and 27h). In this mode, the MAX6640 signals a fan fault when the tachometer count is greater than the maximum tachometer count value stored in the appropriate register (22h and 23h). After the MAX6640 asserts FAN
THERM
When a measured temperature exceeds the corresponding THERM temperature threshold and THERM is not masked, the associated THERM status register bit is set and the THERM output asserts. If THERM for the respective channel is masked, the THERM status register is set, but the THERM output does not assert. To deassert the THERM output and the associated status register bit, either the measured temperature must fall at least 5C below the trip threshold or the trip threshold must be increased to at least 5C above the current measured temperature. Asserting THERM internally or externally forces both PWM outputs to 100% duty cycle when bit 6 in address 13h (fan 1) or bit 6 in address 17h (fan 2) is set.
Table 2. Tachometer Setting
FAN RPM RANGE 2000 4000 8000 16,000 INTERNAL CLOCK FREQUENCY (kHz) 1 2 4 8
ALERT
The ALERT output asserts to indicate that a measured temperature exceeds the ALERT trip threshold for that
8
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2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller
FAIL, the fan with a tachometer fault goes to full speed for 2s in an attempt to restart the fan and then returns to the original duty-cycle settings. Reading the status register clears the FANFAIL status bits and the output. The MAX6640 measures the fan speed again after 2s. The MAX6640 asserts FANFAIL if it detects the fan fault again. In RPM mode (either automatic or manual), the MAX6640 checks for fan failure only when the duty cycle reaches 100%. It asserts FANFAIL when the tachometer count is greater than twice the target tachometer count. In manual RPM mode, registers 22h and 23h store the target tachometer count value. In automatic RPM mode, these registers store the maximum tachometer count. 14h) to zero. In the manual RPM control mode, the MAX6640 adjusts the duty cycle and measures the fan speed. Enter the target tachometer count in register 22h for fan 1 and register 23h for fan 2. The MAX6640 compares the target tachometer count with the measured tachometer count and adjusts the duty cycle so that the fan speed gradually approaches the target tachometer count. The first time manual RPM control mode is entered, the initial PWM duty cycle is determined by the target tachometer count: Initial duty cycle = 255 - t arg etTACH 2
MAX6640
Fan-Speed Control
The MAX6640 adjusts fan speed by controlling the duty cycle of a PWM signal. This PWM signal then either modulates the DC brushless fan's power supply or drives a speed-control input on a fan that is equipped with one. There are three speed-control modes: PWM, in which the PWM duty cycle is directly programmed over the SMBus; manual RPM, in which the desired tachometer count is programmed into a register and the MAX6640 adjusts its duty cycle to achieve the desired tachometer count; and automatic RPM, in which the tachometer count is adjusted based on a programmed temperature profile. The MAX6640 divides each PWM cycle into 120 time slots. Registers 26h and 27h contain the current values of the duty cycles for PWM1 and PWM2, expressed as the effective time slot length. For example, the PWM1 output duty cycle is 25% when register 26h reads 1Eh (30/120). PWM Control Mode Enter PWM mode by setting bit 7 of the fan 1 or 2 configuration 1 register (10h and 14h) to 1. In PWM control mode, the MAX6640 generates PWM signals whose duty cycles are specified by writing the desired values to fan duty-cycle registers 26h and 27h. When a new duty-cycle value is written into one of the fan duty-cycle registers, the duty cycle changes to the new value at a rate determined by the rate-of-change bits [6:4] in the fan 1 or 2 configuration 1 register. The rate-of-change of the duty cycle ranges from 000 (immediately changes to the new programmed value) to 111 (changes by 1/120 every 4s). See Table 4 and the Fan 1 and 2 Configuration 1 (10h and 14h) section. Manual RPM Control Mode Enter manual RPM control mode by setting bits 2, 3, and 7 of the fan 1 or 2 configuration 1 register (10h and
where targetTACH is the value of the target tachometer count in the target tach count register (22h or 23h). If the initial duty cycle value is over 120, the duty cycle is 100%. If spin-up is enabled (bit 7 in registers 13h and 17h) and the fan is not already spinning, the duty cycle first goes to 100% and then goes to the initial duty-cycle value. Every 2s, the MAX6640 counts the fan's period by counting the number of pulses stored in registers 24h and 25h. If the count is different from the target count, the duty cycle is adjusted. If a nonzero rate-of-change is selected, the duty cycle changes at the specified rate until the tachometer count is within 5 of the target. Then the MAX6640 gets into a locked state and updates the duty cycle every 2s. Automatic RPM Control Mode In the automatic RPM control mode, the MAX6640 measures temperature, sets a target tachometer count based on the measured temperature, and then adjusts the duty cycle so the fan spins at the desired speed. Enter this mode by setting bit 7 of the fan 1 or 2 configuration 1 register (10h and 14h) to zero and selecting the temperature channel that controls the fan speed using bits 2 and 3 of the configuration register. In both the RPM modes (automatic and manual), the MAX6640 implements a low limit for the tachometer counts. This limits the maximum speed of the fan by ensuring that the fan's tachometer count does not go lower than the tachometer count specified by bits 5 through 0 of register 24h for fan 1 and register 25h for fan 2. Typical values for the minimum tachometer count are 30h to 60h. Set the value to correspond to the fullrated RPM of the fan. See Figure 4. Figure 5 shows how the MAX6640 calculates the target tachometer value based on the measured temperature. At TMIN, the fan spins at a minimum speed value corresponding to the maximum tachometer count value
9
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2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller MAX6640
RPM TACH 0xFFh TMIN-5 TMIN TB TEMPERATURE RPMMAX TACHB+1 TACHMAX TACHA+1 RPMMIN TACHB+1 TACHMIN 0 TMIN-5 TMIN TB TEMPERATURE TACHA+1
Figure 4. Tachometer Target Calculation
Figure 5. RPM Target Calculation
stored in register 22h or 23h. Bit 0 of register 11h (fan 1) and register 15h (fan 2) selects the behavior below TMIN. If bit 0 is equal to zero, the fan will be completely off below TMIN. When the temperature is falling, it must drop 5C below TMIN before the fan turns off. If bit 0 is set to 1, the fan does not turn off below T MIN , but instead stays at the maximum tachometer count in register 22h or 23h. When the measured temperature is higher than TMIN, the MAX6640 calculates the target tachometer count value based on two linear equations. The target tachometer count decreases by the tach step size value stored in bits 7 through 4 of registers 11h and 15h each time the measured temperature increases by the temperature step size value stored in bits 2 and 3 of registers 11h and 15h. As the measured temperature continues to increase, a second tachometer step size goes into effect. Bits 3 through 0 of register 12h and 16h select the number temperature/PWM steps after which the new step size takes effect. The new step size is selected by bits 7 to 4 of registers 12h and 16h.
and channel 2 temperature registers do not update until at least 250ms after the access of the associated extended temperature registers. All values below 0C return 00h. Status Register (02h) A 1 indicates that an ALERT, THERM, OT, or fan fault has occurred. Reading this register clears bits 7, 6, 1, and 0. Reading the register also clears the ALERT and FANFAIL outputs, but not the THERM and OT outputs. If the fault is still present on the next temperature measurement cycle, any cleared bits and outputs are set again. A successful alert response clears the values on the outputs but does not clear the status register bits. The ALERT bits assert when the measured temperature is higher than the respective thresholds. The THERM and OT outputs behave like comparators with 5C hysteresis. Mask Register (03h) This register masks the ALERT, OT, THERM, and FANFAIL outputs. A 1 prevents the corresponding failures from being asserted on these outputs. The mask bits do not affect the status register. Global Configuration Register (04h) The global configuration register controls the shutdown mode, power-on reset, SMBus timeout, and temperature channel 2 source select: * D7: Run/Standby. Normal operation is run (0). Setting this bit to 1 suspends conversions and puts the MAX6640 into low-power sleep mode. * D6: Software POR. Writing a 1 resets all registers to their default values.
Register Descriptions
Channel 1 and Channel 2 Temperature Registers (00h and 01h) These registers contain the results of temperature measurements. The MSB has a weight of +128C and the LSB +1C. Temperature data for remote diode 1 is in the channel 1 temperature register. Temperature data for remote diode 2 or the local sensor (selectable by bit 4 in the global configuration register) is in the channel 2 temperature register. Three additional temperature bits provide resolution down to 0.125C and are in the channel 1 extended temperature (05h) and channel 2 extended temperature (06h) registers. The channel 1
10
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2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller
Table 3. Register Map
READ/ WRITE R R R R/W REGISTER POR FUNCTION NO. STATE ADDRESS 00h 01h 02h 03h 0000 0000 0000 0000 0000 0000 0000 0011 D7 D6 D5 D4 D3 D2 D1 D0 LSB (1C) LSB (1C) Fan 2 fault Fan 2 fault
MAX6640
Temperature MSB channel 1 (+128C) Temperature MSB channel 2 (+128C) Status byte Output mask
-- --
-- --
-- --
-- --
-- --
-- --
Channel 1 Channel 2 Channel 1 Channel 2 Channel 1 Channel 2 Fan 1 fault ALERT ALERT THERM THERM OT OT Channel 1 Channel 2 Channel 1 Channel 2 Channel 1 Channel 2 Fan 1 fault ALERT ALERT THERM THERM OT OT
R/W
04h
0011 0000
Global configuration
Run 0 = run, 1= stby
POR 1 = reset
SMBus Temp timeout channel 2 0= source: Reserved Reserved Reserved Reserved enabled, 1 = local, 0 = remote 1= disabled 2 LSB Reserved Reserved Reserved Reserved (0.125C) LSB Reserved Reserved Reserved Reserved (0.125C) -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- RPM range select Diode fault Diode fault LSB (1C) LSB (1C) LSB (1C) LSB (1C) LSB (1C) LSB (1C)
R
05h
0000 0000 0000 0000 0101 0101 0101 0101 0110 1110 0110 1110 0101 0101 0101 0101 1000 0010
R
06h
Channel 1 extended temperature Channel 2 extended temperature Channel 1 ALERT limit Channel 2 ALERT limit Channel 1 OT limit Channel 2 OT limit Channel 1 THERM limit Channel 2 THERM limit Fan 1 configuration 1
MSB (0.5C) MSB (0.5C) MSB MSB MSB MSB MSB MSB PWM mode
--
--
R/W R/W R/W R/W R/W R/W
08h 09h 0Ah 0Bh 0Ch 0Dh
-- -- -- -- -- --
R/W
10h
R/W
11h
0000 0000
RPM range select Minimum fan Fan 1 RPM step- Temp Temp PWM RPM stepRPM step- RPM stepspeed Configuration size A size A step-size step-size 100% duty size A size A 0 = 0%, 2a (MSB) (LSB) A (MSB) A (LSB) cycle 1= value
Step-size Step-size Fan 1 Fan 1 Step-size delay delay channel 1 channel 2 delay (MSB) (LSB) control control
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11
2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller MAX6640
Table 3. Register Map (continued)
READ/ WRITE REGISTER POR FUNCTION NO. STATE ADDRESS 12h D7 D6 D5 D4 D3 D2 D1 D0
R/W
RPM stepFan 1 Start RPM Start RPM step- RPM step0000 Start step- Start stepstep-size step-size step-size configuration size B 0000 size B size B size B size B (LSB) 2b (MSB) B B (LSB) B (MSB) Fan 1 0100 configuration 0001 3 Fan 2 1000 configuration 0010 1 Spin-up disable PWM mode Pulse Fan PWM THERM to full-speed stretching Reserved Reserved Reserved frequency disable enable (MSB) Step-size Fan 2 Fan 2 Step-size Step-size delay delay channel 1 channel 2 delay (MSB) (LSB) control control RPM range select PWM 100% duty cycle Fan PWM frequency (LSB) RPM range select Minimum fan speed 0 = 0%, 1= value in 22h
R/W
13h
R/W
14h
R/W
15h
Fan 2 Temp Temp RPM stepRPM 0000 RPM step- RPM stepconfiguration size A step-size step-size step-size 0000 size A size A 2a (MSB) A (LSB) A (MSB) A (LSB)
R/W
16h
Fan 2 Start RPM stepRPM Start 0000 RPM step- RPM stepStart step- Start stepconfiguration size B step-size step-size step-size 0000 size B size B size B size B (LSB) 2b (MSB) B B (LSB) B (MSB) Fan 2 0100 configuration 0001 3 1111 1111 1111 1111 Fan 1 tachometer count Fan 2 tachometer count Fan 1 max tach count/ target tach count Fan 2 max tach count/ target tach count Pulses per revolution/ fan 1 minimum tach count Pulses per revolution/ fan 2 minimum tach count Spin-up disable Pulse Fan PWM THERM to full-speed stretching Reserved Reserved Reserved frequency (MSB) disable enable -- -- -- -- -- -- Fan PWM frequency (LSB) LSB
R/W
17h
R
20h
MSB
R
21h
MSB
--
--
--
--
--
--
LSB
R/W
22h
1111 1111
MSB
--
--
--
--
--
--
LSB
R/W
23h
1111 1111
MSB
--
--
--
--
--
--
LSB
R/W
24h
0100 0000
Pulse per Pulse per Fan 1 min Fan 1 min Fan 1 min Fan 1 min Fan 1 min revolution revolution tach count tach tach tach tach (MSB) (LSB) count count count count (MSB)
Fan 1 min tach count (LSB)
R/W
25h
0100 0000
Pulse per Pulse per Fan 2 min Fan 2 min Fan 2 min Fan 2 min Fan 2 min tach tach tach tach revolution revolution tach count (MSB) (MSB) (LSB) count count count count
Fan 2 min tach count (LSB)
R
26h
0000 Fan 1 current 0000 duty cycle
MSB
--
--
--
--
--
--
LSB
12
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2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller
Table 3. Register Map (continued)
READ/ WRITE W R W REGISTER POR NO. FUNCTION STATE ADDRESS 26h 27h 27h 0011 1100 0000 0000 0011 1100 0100 000 Fan 1 target duty cycle Fan 2 current duty cycle Fan 2 target duty cycle Channel 1 minimum fan-start temperature Channel 2 minimum fan-start temperature Read device ID Read manufacturer ID Read device revision D7 D6 D5 D4 D3 D2 D1 D0
MAX6640
MSB MSB MSB
-- -- --
-- -- --
-- -- --
-- -- --
-- -- --
-- -- --
LSB LSB LSB
R/W
28h
MSB
--
--
--
--
--
--
LSB
R/W
29h
0100 0000 0101 1000 0100 1101 0000 0000
MSB
--
--
--
--
--
--
LSB
R
3Dh
0
1
0
1
1
0
0
0
R
3Eh
0
1
0
0
1
1
0
1
R
3Fh
0
0
0
0
0
0
0
0
* D5: SMBus Timeout Disable. Writing a zero enables SMBus timeout for prevention of bus lockup. When the timeout function is enabled, the SMBus interface is reset if SDA or SCL remains low for more than 74ms (typ). * D4: Temperature Channel 2 Source. Selects either local or remote 2 as the source for temperature channel 2 register data. Writing a zero to this bit selects remote 2 for temperature channel 2. Extended Temperature Registers (05h and 06h) These registers contain the extended temperature data from channels 1 and 2. Bits D[7:5] contain the 3 LSBs of the temperature data. The bit values are 0.5C, 0.25C, and 0.125C. When bit 0 is set to 1, a diode fault has been detected. Channel 1 and Channel 2 ALERT, OT, and THERM Limits (08h Through 0Dh) These registers contain the temperatures above which the ALERT, THERM, and OT status bits set and outputs assert (for the temperature channels that are not masked). The data format is the same as that of the
channel 1 and channel 2 temperature registers: the LSB weight is +1C and the MSB is +128C. Fan 1 and 2 Configuration 1 (10h and 14h) The following registers control the modes of operation of the MAX6640: * D7: PWM Mode. D7 = 1 sets the fan into manual PWM duty-cycle control mode. Write the target duty cycle in the fan duty-cycle register. D7 = 0 puts the fan into RPM control mode. To set RPM manually, set both fan-control temperature channels (bits D2 and D3) to zero and write the desired tachometer count into the TACH count register. * D[6:4]: Fan Duty-Cycle Rate-of-Change. D[6:4] sets the time between increments of the duty cycle. Each increment is 1/120 of the duty cycle. By adjusting the rate of change, audibility of fan-speed changes can be traded for response time. Table 4 shows the effect of D[6:4] and, for reference, the time required for the fan speed to change from 33% to 100% duty cycle as a function of the rate-ofchange bits.
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13
2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller MAX6640
Table 4. Fan Duty-Cycle Rate-of-Change
REGISTER 10h OR 14h D[6:4] 000 001 010 011 100 101 110 111 NOMINAL RATE OF CHANGE (s) 0 0.0625 0.125 0.25 0.5 1 2 4 ACTUAL RATE OF CHANGE AT SPECIFIC PWM FREQUENCIES 100Hz (s) 0 0.06 0.13 0.25 0.5 1 2 4 50Hz (s) 0 0.06 0.12 0.26 0.5 1 2 4 33.3Hz (s) 0 0.06 0.12 0.24 0.51 0.99 1.98 3.96 20Hz (s) 0 0.05 0.15 0.25 0.5 1 2 4 NOMINAL TIME FROM 33% TO 100% (s) 0 5 10 20 40 80 160 320
* D[3:2]: Temperature Channel(s) for Fan Control. Selects the temperature channel(s) that control the PWM output when the MAX6640 is in automatic RPM control mode (PWM mode bit is zero). If two channels are selected, the fan goes to the higher of the two possible speeds. If neither channel is selected, then the fan is in manual RPM mode and the speed is forced to the value written to the target tach count register 22h or 23h. * D[1:0]: RPM Range. Scales the tachometer counter by setting the maximum (full-scale) value of the RPM range to 2000, 4000, 8000, or 16,000. (Table 2 shows the internal clock frequency as a function of the range.)
Fan 1 and 2 Configuration 2a (11h and 15h) The following registers apply to the automatic RPM control mode: * D[7:4]: Fan RPM (Tachometer) Step-Size A. Selects the number of tachometer counts the target value decreases for each temperature step increase above the fan-start temperature. Value = n + 1 (1 through 16) where n is the value of D[7:4]. * D[3:2]: Temperature Step Size. Selects the temperature increment for fan control. For each temperature step increase, the target tachometer count decreases by the value selected by D[7:4] (Table 7). * D1: PWM Output Polarity. PWM output is low at 100% duty cycle when this bit is set to zero. PWM output is high at 100% duty cycle when this bit is set to 1. * D0: Minimum Speed. Selects the value of the minimum fan speed (when temperature is below the fanstart temperature in the automatic RPM control mode). Set to zero for 0% fan drive. Set to 1 to determine the minimum fan speed by the tachometer count value in registers 22h and 23h (fan maximum TACH).
Table 5. Fan RPM Speed
D[1:0] 00 01 10 11 FAN MAXIMUM RPM VALUE 2000 4000 8000 16,000
Table 6. RPM to Tachometer Count Relationship Examples
MAXIMUM RPM VALUE 2000 4000 4000 4000 16,000 ACTUAL RPM 1000 1000 3000 3000 8000 SELECTED NUMBER OF PULSES PER REVOLUTION 2 2 2 2 4 ACTUAL FAN PULSES PER REVOLUTION 2 2 2 4 4 TACHOMETER COUNT VALUE* 3Ch 78h 28h 14h 3Ch
16,000 8000 4 2 78h *Tachometer count value = ((internal clock frequency) x 60) / actual RPM) (selected number of pulses per revolution / actual fan pulses)
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2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller
Table 7. Temperature Step Size
D[3:2] 00 01 10 11 FAN CONTROL TEMPERATURE STEP SIZE (C) 1 2 4 8
Table 8. Fan PWM Frequency
D[1:0] 00 01 10 11 LOW FREQUENCY (Hz) 20 33.33 50 100
MAX6640
Fan 1 and 2 Configuration 2b (12h and 16h) The following registers select the tachometer step sizes and number of steps for step-size A to step-size B slope changes (see Figure 1): * D[7:4]: RPM (Tachometer) Step Size B. Selects number of tachometer counts the target value decreases for each temperature step increase after the number of steps selected by D[3:0]. Value = n + 1 (1 through 16) where n is the value of D[7:4]. * D[3:0]: Selects the number of temperature/tachometer steps above the fan-start temperature at which step-size B begins. Fan 1 and Fan 2 Configuration 3 (13h and 17h) The following registers control fan spin-up, PWM output frequency, pulse stretching, and THERM to fan fullspeed enable: * D7: Fan Spin-Up Disable. Set to zero to enable fan spin-up. Whenever the fan starts up from zero drive, it is driven with 100% duty cycle for 2s to ensure that it starts. Set to 1 to disable the spin-up function. * D6: THERM to Full-Speed Enable. When this bit is 1, THERM going low (either by being pulled low externally or by the measured temperature exceeding the THERM limit) forces the fan to full speed. In all modes, this happens at the rate determined by the rate-of-change selection. When THERM is deasserted (even if fan has not reached full speed), the speed falls at the selected rate-of-change to the target speed. * D5: Disable Pulse Stretching. Pulse stretching is enabled when this bit is set to zero. When modulating the fan's power supply with the PWM signal, the PWM pulses are periodically stretched to keep the tachometer signal available for one full revolution. Setting this bit to 1 disables pulse stretching. The MAX6640 still measures the fan speed but does not stretch the pulses for measurements, so the fan's power supply must not be pulse modulated. * D[1:0]: PWM Output Frequency. These bits control the PWM output frequency as shown in Table 8.
Fan Tach Count 1 and 2 (20h and 21h) These registers have the latest tachometer measurement of the corresponding channel. This is inversely proportional to the fan's speed. The fan RPM range should be set so this count falls in the 30 to 160 range for normal fan operation. Fan Start Tach Count/Target Tach Count (22h and 23h) D[7:0]: This sets the starting tachometer count for the fan in automatic RPM mode. Depending on the setting of the minimum duty-cycle bit, the tachometer count has this value either at all temperatures below the fanstart temperature or the count is zero below the fanstart temperature and has this value when the fan-start temperature is reached. These registers are the target tach count when in manual RPM mode. Fan 1 and 2 Pulses and Min RPM (24h and 25h) D[7:6]: This sets the number of tachometer pulses per revolution for the fan. When set properly, a 2000RPM fan with two pulses per revolution has the same tachometer count as a 2000RPM fan with four pulses per revolution. Table 9 lists tachometer pulses per revolution. D[5:0]: This sets the minimum allowable fan tachometer count (maximum speed). This limits the maximum speed of the fan to reduce noise at high temperatures. For reasonable speed resolution, the fan RPM range should be set so this value is between about 30 and 60. If a maximum RPM limit is unnecessary, this value can be set to the full-speed tachometer count. Fan 1 and 2 Duty Cycle (26h and 27h) These registers contain the present value of the PWM duty cycle. In PWM fan-control mode, the desired (target) value of the PWM duty cycle can be written directly into this register. Channel 1 and Channel 2 Fan-Start Temperature (28h and 29h) These registers contain the temperatures at which fan control begins (in automatic RPM mode).
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15
2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller MAX6640
Table 9. Tachometer Pulses per Revolution
D[7:6] 00 01 10 11 TACHOMETER PULSES PER REVOLUTION 1 2 3 4
Applications Information
Fan-Drive Circuits
A variety of fan-drive circuit configurations can be used with the MAX6640 to control the fan's speed. Four of the most common are shown in Figures 6 through 10. PWM Power-Supply Drive (High Side or Low Side) The simplest way to control the speed of a 3-wire (supply, ground, and tachometer output) fan is to modulate its power supply with a PWM signal. The PWM frequency is typically in the 20Hz to 40Hz range, with 33Hz being a common value. If the frequency is too high, the fan's internal control circuitry does not have sufficient time to turn on during a power-supply pulse. If the frequency is too low, the power-supply modulation becomes more easily audible. The PWM can take place on the high side (Figure 6) or the low side (Figure 7) of the fan's power supply. In either case, if the tachometer is used, it is usually necessary to periodically stretch a PWM pulse so there is enough time to count the tachometer pulse edges for
VCC VFAN (5V OR 12V)
speed measurement. The MAX6640 allows this pulse stretching to be enabled or disabled to match the needs of the application. Pulse stretching can sometimes be audible if the fan responds quickly to changes in the drive voltage. If the acoustic effects of pulse stretching are too noticeable, the circuit in Figure 8 can be used to eliminate pulse stretching while still allowing accurate tachometer feedback. The diode connects the fan to a low-voltage power supply, which keeps the fan's internal circuitry powered even when the PWM drive is zero. Therefore, the tachometer signal is always available and pulse stretching can be turned off. Note that this approach prevents the fan from turning completely off, so even when the duty cycle is 0%, the fan may still spin.
Linear Fan Supply Drive
While many fans are compatible with PWM power-supply drive, some are excessively noisy with this approach. When this is the case, a good alternative is to control the fan's power-supply voltage with a variable DC powersupply circuit. The circuit in Figure 10 accepts the PWM signal as an input, filters the PWM, and converts it to a DC voltage that then drives the fan. To minimize the size of the filter capacitor, use the highest available PWM frequency. Pulse stretching is not necessary when using a linear fan supply. Note that this approach is not as efficient as PWM drive, as the fan's power-supply current flows through the MOSFET, which can have an appreciable voltage across it. The total power is still less than that of a fan running at full speed. Table 10 is a summary of fan-drive options.
VCC VFAN (5V OR 12V) 3V TO 5.5V
4.7k PWM1 3V TO 5.5V TACH1
4.7k
TACH OUTPUT 3V TO 5.5V
4.7k TACH1 TACH OUTPUT
4.7k PWM1
Figure 6. High-Side PWM Drive Circuit 16
Figure 7. Low-Side Drive Circuit
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2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller MAX6640
VCC VFAN (12V OR 5V) 3V TO 5.5V VCC
4.7k PWM1 3V TO 5.5V 5V 4.7k TACH1 TACH OUTPUT TACH1 PWM1
4.7k
3V TO 5.5V
VFAN (5V OR 12V)
4.7k
TACH OUTPUT
Figure 8. High-Side PWM Drive with "Keep-Alive" Supply
VFAN (5V OR 12V) VCC 100k 3.3V
Figure 10. 4-Wire Fan with PWM Speed-Control Input
Quick-Start Guide for 8000RPM 4-Pole (2 Pulses per Revolution) Fan in Automatic RPM Mode Using the Circuit of Figure 7
1) Write 02h to register 11h to set the PWM output to drive the n-channel MOSFET. 2) Write 4Bh to register 22h to set the minimum RPM to 3200.
4.7k 100k PWM1
2N3904
3) Write 5Eh to register 24h to set the pulses per revolution to 2 and to set the maximum RPM speed to 8000RPM. 4) Write 19h to register 28h to set the fan-start temperature to +25C.
10F
33k 3V TO 5V 2.2F 91k 4.7k
5) Write D2h to register 10h to start automatic RPM mode.
TACH1 TACH OUTPUT
Remote-Diode Considerations
TACH OUTPUT
Figure 9. High-Side Linear Drive Circuit
4-Wire Fans
Some fans have an additional, fourth terminal that accepts a logic-level PWM speed-control signal as shown in Figure 10. These fans require no external power circuitry and combine the low noise of linear drive with the high efficiency of PWM power-supply drive. Higher PWM frequencies are recommended when using 4-wire fans.
Temperature accuracy depends upon having a goodquality, diode-connected, small-signal transistor. Accuracy has been experimentally verified for all the devices listed in Table 11. The MAX6640 can also directly measure the die temperature of CPUs and other ICs with on-board temperature-sensing diodes. The transistor must be a small-signal type with a relatively high forward voltage. This ensures that the input voltage is within the A/D input voltage range. The forward voltage must be greater than 0.25V at 10A at the highest expected temperature. The forward voltage must be less than 0.95V at 100A at the lowest expected temperature. The base resistance has to be less than 100. Tight specification of forward-current gain (+50 to +150, for example) indicates that the manufacturer has good process control and that the devices have consistent characteristics.
17
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2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller MAX6640
Table 10. Summary of Fan-Drive Options
FIGURE 6 7 8 9 10 DESCRIPTION High-side PWM drive Low-side PWM drive High-side PWM drive with keep-alive supply High-side linear supply 4-wire fan with PWM speed-control input PULSE STRETCHING Yes Yes No No No PWM FREQUENCY Low Low Low High High PWM POLARITY Negative Positive Negative Positive Positive
Effect of Ideality Factor
The accuracy of the remote temperature measurements depends on the ideality factor (n) of the remote diode (actually a transistor). The MAX6640 is optimized for n = 1.008, which is the typical value for the Intel(R) Pentium(R) III and the AMD Athlon MP model 6. If a sense transistor with a different ideality factor is used, the output data is different. Fortunately, the difference is predictable. Assume a remote-diode sensor designed for a nominal ideality factor nNOMINAL is used to measure the temperature of a diode with a different ideality factor, n1. The measured temperature TM can be corrected using: n1 TM = TACTUAL nNOMINAL where temperature is measured in Kelvin. As mentioned above, the nominal ideality factor of the MAX6640 is 1.008. As an example, assume the MAX6640 is configured with a CPU that has an ideality factor of 1.002. If the diode has no series resistance, the measured data is related to the real temperature as follows:
n 1.008 TACTUAL = TM NOMINAL = TM = TM (1.00599) n1 1.002
Since 1C corresponds to 198.6V, series resistance contributes a temperature offset of: V 90 C = 0.453 V 198.6 C Assume that the diode being measured has a series resistance of 3. The series resistance contributes an offset of: 3 x 0.453 C = 1.36C
The effects of the ideality factor and series resistance are additive. If the diode has an ideality factor of 1.002 and series resistance of 3, the total offset can be calculated by adding error due to series resistance with error due to ideality factor: 1.36C - 2.13C = -0.77C for a diode temperature of +85C. In this example, the effect of the series resistance and the ideality factor partially cancel each other. For best accuracy, the discrete transistor should be a small-signal device with its collector connected to GND and base connected to DXN. Table 11 lists examples of discrete transistors that are appropriate for use with the MAX6640.
For a real temperature of +85C (358.15K), the measured temperature is +82.91C (356.02K), which is an error of -2.13C.
Effect of Series Resistance
Series resistance in a sense diode contributes additional errors. For nominal diode currents of 10A and 100A, change in the measured voltage is: VM = RS (100A - 10A) = 90A x RS
Table 11. Remote-Sensor Transistor Manufacturers
MANUFACTURER Central Semiconductor (USA) Rohm Semiconductor (USA) Samsung (Korea) Siemens (Germany) MODEL NO. CMPT3906 SST3906 KST3906-TF SMBT3906
Intel and Pentium are registered trademarks of Intel Corp. 18 ______________________________________________________________________________________
2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller
The transistor must be a small-signal type with a relatively high forward voltage; otherwise, the ADC input voltage range can be violated. The forward voltage at the highest expected temperature must be greater than 0.25V at 10A, and at the lowest expected temperature, the forward voltage must be less than 0.95V at 100A. Large-power transistors must not be used. Also, ensure that the base resistance is less than 100. Tight specifications for forward current gain (50 < fl < 150, for example) indicate that the manufacturer has good process controls and that the devices have consistent VBE characteristics. in value. Cable resistance also affects remote-sensor accuracy. A 1 series resistance introduces about +1/2C error.
MAX6640
PC Board Layout Checklist
1) Place the MAX6640 as close as practical to the remote diode. In a noisy environment, such as a computer motherboard, this distance can be 4in to 8in, or more, as long as the worst noise sources (such as CRTs, clock generators, memory buses, and ISA/PCI buses) are avoided. 2) Do not route the DXP/DXN lines next to the deflection coils of a CRT. Also, do not route the traces across a fast memory bus, which can easily introduce +30C error, even with good filtering. Otherwise, most noise sources are fairly benign. 3) Route the DXP and DXN traces parallel and close to each other, away from any high-voltage traces such as +12VDC. Avoid leakage currents from PC board contamination. A 20M leakage path from DXP ground causes approximately +1C error. 4) Connect guard traces to GND on either side of the DXP/DXN traces. With guard traces, placing routing near high-voltage traces is no longer an issue. 5) Route as few vias and crossunders as possible to minimize copper/solder thermocouple effects. 6) When introducing a thermocouple, make sure that both the DXP and the DXN paths have matching thermocouples. In general, PC board-induced thermocouples are not a serious problem. A copper solder thermocouple exhibits 3V/C, and it takes approximately 200V of voltage error at DXP/DXN to cause a +1C measurement error, so most parasitic thermocouple errors are swamped out. 7) Use wide traces. Narrow traces are more inductive and tend to pick up radiated noise. The 10-mil widths and spacings recommended are not absolutely necessary (as they offer only a minor improvement in leakage and noise), but use them where practical. 8) Placing an electrically clean copper ground plane between the DXP/DXN traces and traces carrying high-frequency noise signals helps reduce EMI.
ADC Noise Filtering
The integrating ADC has inherently good noise rejection, especially of low-frequency signals such as 60Hz/120Hz power-supply hum. Micropower operation places constraints on high-frequency noise rejection. Lay out the PC board carefully with proper external noise filtering for high-accuracy remote measurements in electrically noisy environments. Filter high-frequency electromagnetic interference (EMI) at DXP and DXN with an external 2200pF capacitor connected between the two inputs. This capacitor can be increased to about 3300pF (max), including cable capacitance. A capacitance higher than 3300pF introduces errors due to the rise time of the switchedcurrent source.
Twisted Pairs and Shielded Cables
For remote-sensor distances longer than 8in, or in particularly noisy environments, a twisted pair is recommended. Its practical length is 6ft to 12ft (typ) before noise becomes a problem, as tested in a noisy electronics laboratory. For longer distances, the best solution is a shielded twisted pair like that used for audio microphones. For example, Belden #8451 works well for distances up to 100ft in a noisy environment. Connect the twisted pair to DXP and DXN and the shield to ground, and leave the shield's remote end unterminated. Excess capacitance at DXN or DXP limits practical remote-sensor distances (see the Typical Operating Characteristics). For very long cable runs, the cable's parasitic capacitance often provides noise filtering, so the recommended 2200pF capacitor can often be removed or reduced
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19
2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller MAX6640
Typical Operating Circuit
5V VFAN (5V TO 12V)
3.3V TO 5.5V 5V CPU DXP1 DXN DXP2 VCC TACH1 VFAN
PWM1
5V
PWM2
MAX6640
GPU TO SMBus MASTER SDA SCL TACH2 3.3V TO 5.5V
3.3V TO 5.5V
3.3V TO 5.5V
ALERT 3.3V TO 5.5V
OT 3.3V TO 5.5V
TO SYSTEM SHUTDOWN
TO CLOCK THROTTLE
THERM GND
FANFAIL
Chip Information
TRANSISTOR COUNT: 39,135 PROCESS: BiCMOS
20
______________________________________________________________________________________
2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
MAX6640
0.15 C A
D2
C L
D D/2
0.15 C B
b D2/2
0.10 M C A B
k
MARKING
XXXXX
E/2 E2/2 E (NE-1) X e
C L
E2
k L
PIN # 1 I.D.
DETAIL A
e (ND-1) X e
PIN # 1 I.D. 0.35x45 DETAIL B
e
L1
L
C L
C L
L
L
e 0.10 C A 0.08 C
e
C
A1 A3 PACKAGE OUTLINE, 16, 20, 28, 32L THIN QFN, 5x5x0.8mm
-DRAWING NOT TO SCALE-
21-0140
F
1
2
COMMON DIMENSIONS PKG. 16L 5x5 20L 5x5 28L 5x5 32L 5x5 SYMBOL MIN. NOM. MAX. MIN. NOM. MAX. MIN. NOM. MAX. MIN. NOM. MAX. A A1 A3 b D E e k L L1 N ND NE JEDEC 0.70 0.75 0.80 0.70 0.75 0.80 0.70 0.75 0.80 0.70 0.75 0.80 0 0.02 0.05 0.20 REF. 0 0.02 0.05 0.20 REF. 0 0.02 0.05 0.20 REF. 0 0.02 0.05 0.20 REF. PKG. CODES T1655-1 T1655-2 T1655N-1 T2055-2 T2055-3 T2055-4 T2055-5 T2855-1 T2855-2 T2855-3 T2855-4 T2855-5 T2855-6 T2855-7 T2855-8 T2855N-1 T3255-2 T3255-3 T3255-4 T3255N-1
EXPOSED PAD VARIATIONS
D2
MIN. NOM. MAX. MIN.
E2
NOM. MAX.
L
0.15
DOWN BONDS ALLOWED
3.00 3.00 3.00 3.00 3.00 3.00 3.15 3.15 2.60 3.15 2.60 2.60 3.15 2.60 3.15 3.15 3.00 3.00 3.00 3.00
3.10 3.20 3.00 3.10 3.20 3.00 3.10 3.20 3.00 3.10 3.20 3.00 3.10 3.20 3.00 3.10 3.20 3.00 3.25 3.25 2.70 3.25 2.70 2.70 3.25 2.70 3.25 3.25 3.10 3.10 3.10 3.10 3.35 3.35 2.80 3.35 2.80 2.80 3.35 2.80 3.35 3.35 3.20 3.20 3.20 3.20 3.15 3.15 2.60 3.15 2.60 2.60 3.15 2.60 3.15 3.15 3.00 3.00 3.00 3.00
3.10 3.20 3.10 3.20 3.10 3.20 3.10 3.10 3.10 3.25 3.25 2.70 3.25 2.70 2.70 3.25 2.70 3.25 3.25 3.10 3.10 3.10 3.10 3.20 3.20 3.20 3.35 3.35 2.80 3.35 2.80 2.80 3.35 2.80 3.35 3.35 3.20 3.20 3.20 3.20
0.25 0.30 0.35 0.25 0.30 0.35 0.20 0.25 0.30 0.20 0.25 0.30 4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10 0.80 BSC. 0.65 BSC. 0.50 BSC. 0.50 BSC. 0.25 - 0.25 - 0.25 - 0.25 0.30 0.40 0.50 0.45 0.55 0.65 0.45 0.55 0.65 0.30 0.40 0.50 16 4 4 WHHB 20 5 5 WHHC 28 7 7 WHHD-1 32 8 8 WHHD-2 -
** ** ** ** ** ** 0.40 ** ** ** ** ** ** ** 0.40 ** ** ** ** **
NO YES NO NO YES NO Y NO NO YES YES NO NO YES Y N NO YES NO NO
NOTES: 1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994. 2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES. 3. N IS THE TOTAL NUMBER OF TERMINALS. 4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE.
** SEE COMMON DIMENSIONS TABLE
5. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.25 mm AND 0.30 mm FROM TERMINAL TIP. 6. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY. 7. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION. 8. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS. 9. DRAWING CONFORMS TO JEDEC MO220, EXCEPT EXPOSED PAD DIMENSION FOR T2855-1, T2855-3 AND T2855-6. 10. WARPAGE SHALL NOT EXCEED 0.10 mm. 11. MARKING IS FOR PACKAGE ORIENTATION REFERENCE ONLY. 12. NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY. PACKAGE OUTLINE, 16, 20, 28, 32L THIN QFN, 5x5x0.8mm
-DRAWING NOT TO SCALE-
21-0140
F
2
2
______________________________________________________________________________________
QFN THIN.EPS
21
2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller MAX6640
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
QSOP.EPS
PACKAGE OUTLINE, QSOP .150", .025" LEAD PITCH
21-0055
E
1
1
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
22 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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