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19-1483; Rev 0; 4/99
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
________________General Description
The MAX1619 is a precise digital thermometer that reports the temperature of both a remote sensor and its own package. The remote sensor is a diode-connected transistor--typically a low-cost, easily mounted 2N3904 NPN type--that replaces conventional thermistors or thermocouples. Remote accuracy is 3C for multiple transistor manufacturers, with no calibration needed. The remote channel can also measure the die temperature of other ICs, such as microprocessors, that contain an on-chip, diode-connected transistor. The 2-wire serial interface accepts standard System Management Bus (SMBus(R)) Write Byte, Read Byte, Send Byte, and Receive Byte commands to program the alarm thresholds and to read temperature data. The data format is 7 bits plus sign, with each bit corresponding to 1C, in two's complement format. Measurements can be done automatically and autonomously, with the conversion rate programmed by the user or programmed to operate in a single-shot mode. The adjustable rate allows the user to control the supply-current drain. The MAX1619 is nearly identical to the popular MAX1617A, with the additional feature of an overtemperature alarm output (OVERT) that responds to the remote temperature; this is optimal for fan control.
____________________________Features
o Two Channels Measure Both Remote and Local Temperatures o No Calibration Required o SMBus 2-Wire Serial Interface o Programmable Under/Overtemperature Alarms o OVERT Output for Fan Control o Supports SMBus Alert Response o Supports Manufacturer and Device ID Codes o Accuracy 2C (+60C to +100C, local) 3C (-40C to +125C, local) 3C (+60C to +100C, remote) o 3A (typ) Standby Supply Current o 70A (max) Supply Current in Auto-Convert Mode o +3V to +5.5V Supply Range o Write-Once Protection o Small 16-Pin QSOP Package
MAX1619
________________________Applications
Desktop and Notebook Computers Smart Battery Packs LAN Servers Industrial Controls Central Office Telecom Equipment Test and Measurement Multichip Modules
PART MAX1619MEE
Ordering Information
TEMP. RANGE -55C to +125C PIN-PACKAGE 16 QSOP
Typical Operating Circuit
0.1F +3V TO +5.5V 200
___________________Pin Configuration
TOP VIEW
VCC 1 GND 2 DXP 3 DXN 4 N.C. 5 ADD1 6 GND 7 GND 8 16 N.C. 15 STBY
VCC
STBY 10k EACH
MAX1619
DXP SMBCLK SMBDATA 2N3904 DXN 2200pF ALERT OVERT ADD0 ADD1 GND CLOCK DATA INTERRUPT TO C FAN CONTROL
14 SMBCLK
MAX1619
13 N.C. 12 SMBDATA 11 ALERT 10 ADD0 9 OVERT
QSOP
SMBus is a registered trademark of Intel Corp.
________________________________________________________________ Maxim Integrated Products 1
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Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface MAX1619
ABSOLUTE MAXIMUM RATINGS
VCC to GND ..............................................................-0.3V to +6V DXP, ADD_ to GND ....................................-0.3V to (VCC + 0.3V) DXN to GND ..........................................................-0.3V to +0.8V SMBCLK, SMBDATA, ALERT, OVERT, STBY to GND............................................................-0.3V to +6V SMBDATA, ALERT, OVERT Current....................-1mA to +50mA DXN Current .......................................................................1mA ESD Protection (all pins, Human Body Model) ..................2000V Continuous Power Dissipation (TA = +70C) QSOP (derate 8.30mW/C above +70C) .....................667mW Operating Temperature Range .........................-55C to +125C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10sec) .............................+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 = +3.3V, TA = 0C to +85C, configuration byte = XCh, unless otherwise noted.) PARAMETER ADC AND POWER SUPPLY Temperature Resolution (Note 1) Initial Temperature Error, Local Diode (Note 2) Temperature Error, Remote Diode (Notes 2, 3) Temperature Error, Local Diode (Notes 1, 2) Supply Voltage Range Undervoltage Lockout Threshold Undervoltage Lockout Hysteresis Power-On Reset Threshold POR Threshold Hysteresis Logic inputs forced to VCC or GND SMBus static Hardware or software standby, SMBCLK at 10kHz 0.25 conv/sec 2.0 conv/sec 94 -25 High level Low level 80 8 100 10 0.7 ADD0, ADD1; momentary upon power-on reset 160 VCC, falling edge 1.0 VCC input, disables A/D conversion, rising edge Monotonicity guaranteed TA = +60C to +100C TA = 0C to +85C TR = +60C to +100C TR = -55C to +125C (Note 4) Including long-term drift TA = +60C to +100C TA = 0C to +85C 8 -2 -3 -3 -5 -2.5 -3.5 3.0 2.60 2.80 50 1.7 50 3 5 35 120 125 70 A 180 156 25 120 12 ms % A V A 10 A 2.5 2 3 3 5 2.5 3.5 5.5 2.95 Bits C C C V V mV V mV CONDITIONS MIN TYP MAX UNITS
Standby Supply Current
Average Operating Supply Current Conversion Time Conversion Rate Timing Error Remote-Diode Source Current DXN Source Voltage Address Pin Bias Current
Autoconvert mode, average measured over 4sec. Logic inputs forced to VCC or GND.
From stop bit to conversion complete (both channels) Auto-convert mode DXP forced to 1.5V
2
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Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.3V, TA = 0C to +85C, configuration byte = XCh, unless otherwise noted.) PARAMETER SMBus INTERFACE Logic Input High Voltage Logic Input Low Voltage Logic Output Low Sink Current ALERT, OVERT Output High Leakage Current Logic Input Current SMBus Input Capacitance SMBus Clock Frequency SMBCLK Clock Low Time SMBCLK Clock High Time SMBus Start-Condition Setup Time SMBus Repeated Start-Condition Setup Time SMBus Start-Condition Hold Time SMBus Stop-Condition Setup Time SMBus Data Valid to SMBCLK Rising-Edge Time SMBus Data-Hold Time SMBCLK Falling Edge to SMBus Data-Valid Time tSU:STA, 90% to 90% points tHD:STA, 10% of SMBDATA to 90% of SMBCLK tSU:STO, 90% of SMBCLK to 10% of SMBDATA tSU:DAT, 10% or 90% of SMBDATA to 10% of SMBCLK tHD:DAT (Note 6) Master clocking in data STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V ALERT, OVERT, SMBDATA forced to 0.4V ALERT, OVERT, forced to 5.5V Logic inputs forced to VCC or GND SMBCLK, SMBDATA (Note 5) tLOW, 10% to 10% points tHIGH, 90% to 90% points DC 4.7 4 4.7 500 4 4 250 0 1 -1 5 100 6 1 1 2.2 0.8 V V mA A A pF kHz s s s ns s s ns s s CONDITIONS MIN TYP MAX UNITS
MAX1619
ELECTRICAL CHARACTERISTICS
(VCC = +3.3V, TA = -55C to +125C, configuration byte = XCh, unless otherwise noted.) (Note 4) PARAMETER ADC AND POWER SUPPLY Temperature Resolution (Note 1) Initial Temperature Error, Local Diode (Note 2) Temperature Error, Remote Diode (Notes 2, 3) Supply Voltage Range Conversion Time Conversion Rate Timing Error From stop bit to conversion complete (both channels) Autoconvert mode Monotonicity guaranteed TA = +60C to +100C TA = -55C to +125C TR = +60C to +100C TR = -55C to +125C 8 -2 -3 -3 -5 3.0 94 -25 125 2 3 3 5 5.5 156 25 Bits C C V ms % CONDITIONS MIN TYP MAX UNITS
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3
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface MAX1619
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.3V, TA = -55C to +125C, configuration byte = XCh, unless otherwise noted.) (Note 4) PARAMETER SMBus INTERFACE Logic Input High Voltage Logic Input Low Voltage Logic Output Low Sink Current ALERT, OVERT Output High Leakage Current Logic Input Current STBY, SMBCLK, SMBDATA VCC = 3V VCC = 5.5V 2.2 2.4 0.8 6 1 -2 2 V V mA A A CONDITIONS MIN TYP MAX UNITS
STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V ALERT, OVERT, SMBDATA forced to 0.4V ALERT, OVERT forced to 5.5V Logic inputs forced to VCC or GND
Note 1: Guaranteed but not 100% tested. Note 2: Quantization error is not included in specifications for temperature accuracy. For example, if the MAX1619 device temperature is exactly +66.7C, the ADC may report +66C, +67C, or +68C (due to the quantization error plus the +1/2C offset used for rounding up) and still be within the guaranteed 1C error limits for the +60C to +100C temperature range (Table 2). Note 3: A remote diode is any diode-connected transistor from Table 1. TR is the junction temperature of the remote diode. See Remote Diode Selection for remote diode forward voltage requirements. Note 4: Specifications from -55C to +125C are guaranteed by design, not production tested. Note 5: The SMBus logic block is a static design that works with clock frequencies down to DC. While slow operation is possible, it violates the 10kHz minimum clock frequency and SMBus specifications, and may monopolize the bus. Note 6: Note that a transition must internally provide at least a hold time in order to bridge the undefined region (300ns max) of SMBCLK's falling edge.
__________________________________________Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
TEMPERATURE ERROR vs. PC BOARD RESISTANCE
MAX1619-01
TEMPERATURE ERROR vs. REMOTE-DIODE TEMPERATURE
MAX1619-02
TEMPERATURE ERROR vs. POWER-SUPPLY NOISE FREQUENCY
VIN = SQUARE WAVE APPLIED TO VCC WITH NO 0.1F VCC CAPACITOR VIN = 250mVp-p REMOTE DIODE VIN = 100mVp-p LOCAL DIODE VIN = 100mVp-p REMOTE DIODE
MAX1619-03
20 15 TEMPERATURE ERROR (C) 10 PATH = DXP TO GND 5 0 -5 -10 -15 -20 1 10 LEAKAGE RESISTANCE (M) PATH = DXP TO VCC (5V)
2
12
TEMPERATURE ERROR (C)
TEMPERATURE ERROR (C)
1 ZETEX FMMT3904 0 MOTOROLA MMBT3904 -1 RANDOM SAMPLES -2
9
6
3
0 -50 0 50 TEMPERATURE (C) 100 150 50 500 5k 50k 500k 5M 50M FREQUENCY (Hz)
100
4
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Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
MAX1619
TEMPERATURE ERROR vs. COMMON-MODE NOISE FREQUENCY
VIN = SQUARE WAVE AC-COUPLED TO DXN TEMPERATURE ERROR (C) 8 VIN = 100mVp-p
MAX1619-04
TEMPERATURE ERROR vs. DXP-DXN CAPACITANCE
VCC = 5V TEMPERATURE ERROR (C)
MAX1619-07
STANDBY SUPPLY CURRENT vs. CLOCK FREQUENCY
MAX1619-08
10
20
50
40
SUPPLY CURRENT (A)
6
30 VCC = 5V VCC = 3.3V
10
4
VIN = 50mVp-p VIN = 25mVp-p
20
2
10
0 0.1 1 10 100 FREQUENCY (MHz)
0 0 20 40 60 80 100 DXP-DXN CAPACITANCE (nF)
0 1 10 100 1000 SMBCLK FREQUENCY (kHz)
STANDBY SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX1619-09
OPERATING SUPPLY CURRENT vs. CONVERSION RATE
MAX1619-10
INTERNAL DIODE RESPONSE TO THERMAL SHOCK
MAX1619-11
100 ADD0, ADD1 = GND 60 SUPPLY CURRENT (A)
500 VCC = 5V AVERAGED MEASUREMENTS 400 SUPPLY CURRENT (A)
125
100 TEMPERATURE (C)
20
ADD0, ADD1 = HIGH-Z
300
75
6
200
50
3
100
25 16-QSOP IMMERSED IN +115C FLUORINERT BATH
0 0 1 2 3 4 5 SUPPLY VOLTAGE (V)
0 0 0.0625 0.125 0.25 0.5 1 2 4 8 CONVERSION RATE (Hz)
0 -2 0 2 4 TIME (sec) 6 8 10
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5
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface MAX1619
Pin Description
PIN 1 2 3 NAME VCC GND DXP FUNCTION Supply Voltage Input, 3V to 5.5V. Bypass to GND with a 0.1F capacitor. A 200 series resistor is recommended but not required for additional noise filtering. Not internally connected. Connect to GND to act against leakage paths from VCC to DXP. Combined Current Source and A/D Positive Input for Remote-Diode Channel. Do not leave DXP floating; connect DXP to DXN if no remote diode is used. Place a 2200pF capacitor between DXP and DXN for noise filtering. Combined Current Sink and A/D Negative Input. DXN is normally internally biased to a diode voltage above ground. No Connection. Not internally connected. May be used for PC board trace routing. SMBus Address Select Pin (Table 8). ADD0 and ADD1 are sampled upon power-up. Excess capacitance (>50pF) at the address pins when floating may cause address-recognition problems. Ground Overtemperature Alarm Output, Open Drain. This is an unlatched alarm output that responds only to the remote diode temperature. SMBus Slave Address Select Pin SMBus Alert (interrupt) Output, Open Drain SMBus Serial-Data Input/Output, Open Drain SMBus Serial-Clock Input Hardware Standby Input. Temperature and comparison threshold data are retained in standby mode. Low = standby mode, high = operate mode.
4 5, 13, 16 6 7, 8 9 10 11 12 14 15
DXN N.C. ADD1 GND OVERT ADD0 ALERT SMBDATA SMBCLK STBY
Detailed Description
The MAX1619 is a temperature sensor designed to work in conjunction with an external microcontroller (C) or other intelligence in thermostatic, process-control, or monitoring applications. The C is typically a powermanagement or keyboard controller, generating SMBus serial commands either by "bit-banging" general-purpose input/output (GPIO) pins or through a dedicated SMBus interface block. Essentially an 8-bit serial analog-to-digital converter (ADC) with a sophisticated front end, the MAX1619 contains a switched current source, a multiplexer, an ADC, an SMBus interface, and associated control logic (Figure 1). Temperature data from the ADC is loaded into two data registers (local and remote). The remote temperature data is automatically compared with data previously stored in four temperature-alarm threshold registers. One pair of alarm-threshold registers is used to provide hysteretic fan control; the other pair is used for alarm interrupt. The local temperature data is available for monitoring.
6
ADC and Multiplexer
The ADC is an averaging type that integrates over a 60ms period (each channel, typical) with excellent noise rejection. The multiplexer automatically steers bias currents through the remote and local diodes, measures their forward voltages, and computes their temperatures. Both channels are automatically converted once the conversion process has started, either in free-running or single-shot mode. If one of the two channels is not used, the device still performs both measurements, and the user can simply ignore the results of the unused channel. The DXN input is biased at 0.65V above ground by an internal diode to set up the analog-to-digital (A/D) inputs for a differential measurement. The worst-case DXP-DXN differential input voltage range is 0.25V to 0.95V. Excess resistance in series with the remote diode causes about +1/2C error per ohm. Likewise, 200V of offset voltage forced on DXP-DXN causes about 1C error.
_______________________________________________________________________________________
VCC STBY ADD0 ADD1
MUX
2 7 + REMOTE + READ DIODE FAULT 8 8 WRITE LOCAL SMBCLK +
ADDRESS DECODER
MAX1619
DXP
Figure 1. Functional Diagram
DXN
ADC CONTROL LOGIC
SMBDATA
SMBus
GND
8 REMOTE TEMPERATURE DATA REGISTER LOCAL TEMPERATURE DATA REGISTER COMMAND BYTE (INDEX) REGISTER
8 HIGH-TEMPERATURE THRESHOLD (REMOTE THIGH)
HIGH-TEMPERATURE THRESHOLD 8 (REMOTE TMAX)
STATUS BYTE REGISTER
LOW-TEMPERATURE THRESHOLD (REMOTE TLOW) 8 8
HYSTERESIS THRESHOLD (REMOTE THYST)
CONFIGURATION BYTE REGISTER
DIGITAL COMPARATOR (REMOTE)
DIGITAL COMPARATOR (REMOTE OVERTEMP)
CONVERSION RATE REGISTER
ALERT
Q R
S
SELECTED VIA SLAVE ADD = 0001 100
ALERT RESPONSE ADDRESS REGISTER
OVERT S Q R POL
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
MAX1619
_______________________________________________________________________________________
7
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface MAX1619
A/D Conversion Sequence
If a Start command is written (or generated automatically in the free-running auto-convert mode), both channels are converted, and the results of both measurements are available after the end of conversion. A BUSY status bit in the status byte shows that the device is actually performing a new conversion; however, even if the ADC is busy, the results of the previous conversion are always available.
Table 1. Remote-Sensor Transistor Manufacturers
MANUFACTURER Central Semiconductor (USA) Fairchild Semiconductor (USA) Motorola (USA) Rohm Semiconductor (Japan) Siemens (Germany) Zetex (England) MODEL NUMBER CMPT3904 MMBT3904 MMBT3904 SST3904 SMBT3904 FMMT3904CT-ND
Remote-Diode Selection
Temperature accuracy depends on having a good-quality, diode-connected small-signal transistor. Accuracy has been experimentally verified for all the devices listed in Table 1. The MAX1619 can also directly measure the die temperature of CPUs and other integrated circuits having on-board temperature-sensing diodes. The transistor must be a small-signal type with a relatively high forward voltage; otherwise, the A/D input voltage range can be violated. The forward voltage must be greater than 0.25V at 10A; check to ensure this is true at the highest expected temperature. The forward voltage must be less than 0.95V at 100A; check to ensure this is true at the lowest expected temperature. Large power transistors don't work. Also, ensure that the base resistance is less than 100. Tight specifications for forward-current gain (+50 to +150, for example) indicate that the manufacturer has good process controls and that the devices have consistent VBE characteristics. For heatsink mounting, the 500-32BT02-000 thermal sensor from Fenwal Electronics is a good choice. This device consists of a diode-connected transistor, an aluminum plate with screw hole, and twisted-pair cable (Fenwal Inc., Milford, MA, 508-478-6000).
Note: Transistors must be diode-connected (base shorted to collector).
worst-case error occurs when auto-converting at the fastest rate and simultaneously sinking maximum current at the ALERT and OVERT outputs. For example, at an 8Hz rate and with ALERT and OVERT each sinking 1mA, the typical power dissipation is: (VCC)(450A) + 2(0.4V)(1mA) Package JA is about 120C/W, so with VCC = 5V and no copper PC board heatsinking, the resulting temperature rise is: T = 3.1mW(120C/W) = 0.36C Even with these contrived circumstances, it is difficult to introduce significant self-heating errors.
ADC Noise Filtering
The ADC is an integrating type with 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; therefore, careful PC board layout and proper external noise filtering are required for high-accuracy remote measurements in electrically noisy environments. High-frequency EMI is best filtered at DXP and DXN with an external 2200pF capacitor. This value can be increased to about 3300pF (max), including cable capacitance. Capacitance higher than 3300pF introduces errors due to the rise time of the switched current source. Nearly all noise sources tested cause the ADC measurements to be higher than the actual temperature, typically by +1C to +10C, depending on the frequency and amplitude (see Typical Operating Characteristics).
Thermal Mass and Self-Heating
Thermal mass can seriously degrade the MAX1619's effective accuracy. The thermal time constant of the QSOP-16 package is about 4sec in still air. To settle to within +1C after a sudden +100C change, the MAX1619 junction temperature requires about five time constants. The use of smaller packages for remote sensors, such as SOT23s, improves the situation. Take care to account for thermal gradients between the heat source and the sensor, and ensure that stray air currents across the sensor package do not interfere with measurement accuracy. Self-heating does not significantly affect measurement accuracy. Remote-sensor self-heating due to the diode current source is negligible. For the local diode, the
8
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Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
PC Board Layout
1) Place the MAX1619 as close as practical to the remote diode. In a noisy environment, such as a computer motherboard, this distance can be 4 inches to 8 inches (typical) 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 in parallel and in close proximity to each other, away from any highvoltage traces such as +12VDC. Leakage currents from PC board contamination must be dealt with carefully, since a 10M leakage path from DXP to ground causes about +1C error. 4) Connect guard traces to GND on either side of the DXP-DXN traces (Figure 2). With guard traces in place, routing near high-voltage traces is no longer an issue. 5) Route through 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 about 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 ones are more inductive and tend to pick up radiated noise. The 10 mil widths and spacings recommended in Figure 2 aren't absolutely necessary (as they offer only a minor improvement in leakage and noise), but try to use them where practical. 8) Keep in mind that copper can't be used as an EMI shield, and only ferrous materials, such as steel, work well. Placing a copper ground plane between the DXP-DXN traces and traces carrying high-frequency noise signals does not help reduce EMI.
GND 10 MILS 10 MILS DXP MINIMUM 10 MILS DXN 10 MILS GND
MAX1619
Figure 2. Recommended DXP/DXN PC Traces
* Use guard traces flanking DXP and DXN and connecting to GND. * Place the noise filter and the 0.1F V CC bypass capacitors close to the MAX1619. * Add a 200 resistor in series with VCC for best noise filtering (see Typical Operating Circuit).
Twisted Pair and Shielded Cables
For remote-sensor distances longer than 8 inches, or in particularly noisy environments, a twisted pair is recommended. Its practical length is 6 feet to 12 feet (typical) 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, the Belden 8451 works well in a noisy environment for distances up to 100 feet. Connect the twisted pair to DXP and DXN and the shield to GND, and leave the shield's remote end unterminated. Excess capacitance at DX_ limits practical remote sensor distances (see Typical Operating Characteristics). For very long cable runs, the cable's parasitic capacitance often provides noise filtering, so the 2200pF capacitor can often be removed or reduced in value. Cable resistance also affects remote-sensor accuracy; 1 series resistance introduces about +1/2C error.
Low-Power Standby Mode
Standby mode disables the ADC and reduces the supply-current drain to 3A (typical). Enter standby mode by forcing the STBY pin low or via the RUN/STOP bit in the configuration byte register. Hardware and software standby modes behave almost identically: all data is retained in memory, and the SMB interface is alive and listening for reads and writes. The only difference is that in hardware standby mode, the one-shot command does not initiate a conversion. Standby mode is not a shutdown mode. With activity on the SMBus, extra supply current is drawn (see Typical Operating Characteristics). In software standby mode,
9
PC Board Layout Checklist
* Place the MAX1619 close to a remote diode. * Keep traces away from high voltages (+12V bus). * Keep traces away from fast data buses and CRTs. * Use recommended trace widths and spacings. * Place a ground plane under the traces.
_______________________________________________________________________________________
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface MAX1619
the MAX1619 can be forced to perform A/D conversions via the one-shot command, despite the RUN/STOP bit being high. Activate hardware standby mode by forcing the STBY pin low. In a notebook computer, this line may be connected to the system SUSTAT# suspend-state signal. The STBY pin low state overrides any software conversion command. If a hardware or software standby command is received while a conversion is in progress, the conversion cycle is truncated, and the data from that conversion is not latched into either temperature reading register. The previous data is not changed and remains available. The OVERT output continues to function in both hardware and software standby modes. If the overtemp limits are adjusted while in standby mode, the digital comparator checks the new values and puts the OVERT pin in the correct state based on the last valid ADC conversion. The last valid ADC conversion may include a conversion performed using the one-shot command. Supply-current drain during the 125ms conversion period is always about 450A. Slowing down the conversion rate reduces the average supply current (see Typical
Write Byte Format
S ADDRESS 7 bits Slave Address: equivalent to chip-select line of a 3-wire interface WR ACK COMMAND 8 bits Command Byte: selects which register you are writing to ACK DATA 8 bits ACK P 1
Operating Characteristics). Between conversions, the instantaneous supply current is about 25A due to the current consumed by the conversion rate timer. In standby mode, supply current drops to about 3A. At very low supply voltages (under the power-on-reset threshold), the supply current is higher due to the address pin bias currents. It can be as high as 100A, depending on ADD0 and ADD1 settings.
SMBus Digital Interface
From a software perspective, the MAX1619 appears as a set of byte-wide registers that contain temperature data, alarm threshold values, or control bits. A standard SMBus 2-wire serial interface is used to read temperature data and write control bits and alarm threshold data. Each A/D channel within the device responds to the same SMBus slave address for normal reads and writes. The MAX1619 employs four standard SMBus protocols: Write Byte, Read Byte, Send Byte, and Receive Byte (Figure 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 multi-master sys-
Data Byte: data goes into the register set by the command byte (to set thresholds, configuration masks, and sampling rate)
Read Byte Format
S ADDRESS 7 bits Slave Address: equivalent to chip-select line 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 RD ACK DATA 8 bits Data Byte: reads from the register set by the command byte /// P
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 ACK P
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
S = Start condition P = Stop condition
Shaded = Slave transmission /// = Not acknowledged
Figure 3. SMBus Protocols
10 ______________________________________________________________________________________
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
tems, since a second master could overwrite the command byte without informing the first master. The temperature data format is 7 bits plus sign in two's complement form for each channel, with each data bit representing 1C (Table 2), transmitted MSB first. Measurements are offset by +1/2C to minimize internal rounding errors; for example, +99.6C is reported as +100C.
MAX1619
Table 2. Data Format (Two's Complement)
TEMP. (C) +130.00 +127.00 +126.50 +126.00 +25.25 +0.50 +0.25 0.00 -0.25 -0.50 -0.75 -1.00 -25.00 -25.50 -54.75 -55.00 -65.00 -70.00 ROUNDED TEMP. (C) +127 +127 +127 +126 +25 +1 0 0 0 0 -1 -1 -25 -25 -55 -55 -65 -65 DIGITAL OUTPUT DATA BITS SIGN 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 MSB 111 111 111 111 001 000 000 000 000 000 111 111 110 110 100 100 011 011 LSB 1111 1111 1111 1110 1001 0001 0000 0000 0000 0000 1111 1111 0111 0111 1001 1001 1111 1111
Alarm Threshold Registers
Two registers store ALERT threshold limits, with hightemperature (THIGH) and low-temperature (TLOW) registers for the remote A/D channel. There are no comparison registers for the local A/D channel. If either measured temperature equals or exceeds the corresponding alarm threshold value, an ALERT interrupt is asserted. The power-on-reset (POR) state of the THIGH register is full scale (0111 1111, or +127C). The POR state of the TLOW register is 1100 1001 or -55C. Two additional alarm threshold registers control the OVERT output (see OVERT Alarm Output section), TMAX and T HYST . The POR state of T MAX is +100C, and THYST is +95C.
OVERT Alarm Output for Fan Control
The OVERT output is an unlatched open-drain output that behaves as a thermostat to control a fan (Figure 4). When using the SMBus interface, the polarity of the OVERT pin (active-low at POR) can be inverted via bit 5 in the configuration byte. OVERT's current state can be read in the status byte. OVERT can also be used to control a fan without system intervention. OVERT goes low when the remote temperature rises above TMAX and won't go high again until the temperature drops below THYST. The power-up default settings for T MAX and T HYST (+100C and +95C, respectively) allow the MAX1619 to be used in standalone thermostat applications where connection to an SMBus serial bus isn't required.
+3V TO +5.5V +12V STBY VCC
MAX1619
SMBUS SERIAL INTERFACE (TO HOST) SMBCLK SMBDATA ALERT DXP
Diode Fault Alarm
There is a continuity fault detector at DXP that detects whether the remote diode has an open-circuit condition. At the beginning of each conversion, the diode fault is checked, and the status byte is updated. This fault detector is a simple voltage detector; if DXP rises above V CC - 1V (typical) due to the diode current source, a fault is detected. Note that the diode fault isn't checked until a conversion is initiated, so immediately after power-on reset the status byte indicates no fault is present, even if the diode path is broken.
2N3904
DXN ADD0 ADD1 GND
OVERT
PGND
Figure 4. Fan Control Application
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Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface MAX1619
If the remote channel is shorted (DXP to DXN or DXP to GND), the ADC reads 0000 0000 so as not to trip either the T HIGH or T LOW alarms at their POR settings. In applications that are never subjected to 0C in normal operation, a 0000 0000 result can be checked to indicate a fault condition in which DXP is accidentally short circuited. Similarly, if DXP is short circuited to VCC, the ADC reads +127C for both remote and local channels, and the ALERT and OVERT outputs are activated. interrupt and reads the Alert Response address, clearing the interrupt. The system may also read the status byte at this time. The condition that caused the interrupt persists, but no new ALERT interrupt is issued. Finally, the host writes a new value to THIGH. This enables the device to generate a new THIGH interrupt if the alert condition still exists.
Alert Response Address
The SMBus Alert Response interrupt pointer provides quick fault identification for simple slave devices that lack the complex, expensive logic needed to be a bus master. Upon receiving an ALERT interrupt signal, the host master can broadcast a Receive Byte transmission to the Alert Response slave address (0001 100). Then any slave device that generated an interrupt attempts to identify itself by putting its own address on the bus (Table 3). The Alert Response can activate several different slave devices simultaneously, similar to the I2CTM General Call. If more than one slave attempts to respond, bus arbitration rules apply, and the device with the lower address code wins. The losing device does not generate an acknowledge and continues to hold the ALERT line low until serviced (implies that the host interrupt input is level-sensitive). Successful reading of the alert response address clears the interrupt latch.
ALERT Interrupts
The ALERT interrupt output signal is latched and can only be cleared by reading the Alert Response address. Interrupts are generated in response to THIGH and TLOW comparisons and when the remote diode is disconnected (for continuity fault detection). The interrupt does not halt automatic conversions; new temperature data continues to be available over the SMBus interface after ALERT is asserted. The interrupt output pin is open-drain so that devices can share a common interrupt line. The interrupt rate can never exceed the conversion rate. The interface responds to the SMBus Alert Response address, an interrupt pointer return-address feature (see Alert Response Address section). Prior to taking corrective action, always check to ensure that an interrupt is valid by reading the current temperature. To prevent reoccurring interrupts, the MAX1619 asserts ALERT only once per crossing of a given temperature threshold. To enable a new interrupt, the value in the limit register that triggered the interrupt must be rewritten. Note that other interrupt conditions can be caused by crossing the opposite temperature threshold, or a diode fault can still cause an interrupt. Example: the remote temperature reading crosses T HIGH, activating ALERT. The host responds to the
Command Byte Functions
The 8-bit command byte register (Table 4) is the master index that points to the other registers within the MAX1619. The register's POR state is 0000 0001 so that a Receive Byte transmission (a protocol that lacks the command byte) that occurs immediately after POR returns the current remote temperature data. The one-shot command immediately forces a new conversion cycle to begin. In software standby mode (RUN/STOP bit = high), a new conversion is begun, after which the device returns to standby mode. If a conversion is in progress when a one-shot command is received, the command is ignored. If a one-shot command is received in auto-convert mode (RUN/STOP bit = low) between conversions, a new conversion begins, the conversion rate timer is reset, and the next automatic conversion takes place after a full delay elapses.
Table 3. Read Format for Alert Response Address (0001100)
BIT 7 (MSB) 6 5 4 3 2 1 0 (LSB) NAME ADD7 ADD6 ADD5 ADD4 ADD3 ADD2 ADD1 1 FUNCTION
Provide the current MAX1619 slave address
Configuration Byte Functions
The configuration byte register (Table 5) is used to mask (disable) interrupts, to put the device in software standby mode, to change the polarity of the OVERT output, and to enable the write-once protection. The lowest two bits are internally set to zeros, making them "don't care" bits. This register's contents can be read back over the serial interface.
Logic 1
I2C is a trademark of Philips Corp.
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Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface MAX1619
Table 4. Command-Byte Bit Assignments
REGISTER RLTS RRTE RSL RCL RCRA RRTM RRTH RRHI RRLS WCA WCRW WRTM WRTH WRHA WRLN OSHT SPOR WADD MFG ID DEV ID COMMAND 00h 01h 02h 03h 04h 10h 11h 07h 08h 09h 0Ah 12h 13h 0Dh 0Eh 0Fh FCh FDh FEh FFh POR STATE 0000 0000* 0000 0000* N/A 0000 1100 0000 0010 01100100 01011111 0111 1111 1100 1001 N/A N/A N/A N/A N/A N/A N/A N/A N/A 0100 1101 0000 0100 FUNCTION Read local temperature: returns latest temperature Read remote temperature: returns latest temperature Read status byte (flags, busy signal) Read configuration byte Read conversion rate byte Read remote TMAX limit Read remote THYST limit Read remote THIGH limit Read remote TLOW limit Write configuration byte Write conversion rate byte Write remote TMAX limit Write remote THYST limit Write remote THIGH limit Write remote TLOW limit One-shot command Write software POR Write address Read manufacturer ID code Read device ID code
*If the device is in hardware standby mode at POR, both temperature registers read 0C.
Table 5. Configuration-Byte Bit Assignments
BIT 7 (MSB) 6 NAME MASK RUN/ STOP POR STATE 0 0 FUNCTION Masks all ALERT interrupts when high. Standby mode control bit. If high, the device immediately stops converting and enters standby mode. If low, the device converts in either one-shot or timer mode. Determines the polarity of the OVERT output: 0 = active low (low when overtemp) 1 = active high When asserted high, locks out all subsequent writes to: [] Configuration register bits 6, 5, 4, 3, 2 (RUN/STOP, POL, PROT, ID1, ID2) [] TMAX register [] THYST register [] Conversion rate register [] Diode Current Reduces the diode current by 5A when set low. Reduces the diode current by 2.5A when set low. Reserved for future use. 13
5
POL
0
4
PROT
0
3 2 1-0
ID1 ID2 RFU
1 1 0
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Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface MAX1619
Table 6. Status-Byte Bit Assignments
BIT 7 (MSB) 6 5 4 3 2 1 0 (LSB) NAME BUSY RFU RFU RHIGH* RLOW* OPEN* OVER RFU FUNCTION A high indicates that the ADC is busy converting. Reserved for future use. Reserved for future use. A high indicates that the remote hightemperature alarm has activated. A high indicates that the remote lowtemperature alarm has activated. A high indicates a remote-diode continuity (open-circuit) fault. This bit follows the state of the OVERT pin exactly, in real time (unlatched). Reserved for future use. 00h 01h 02h 03h 04h 05h 06h 07h 08h to FFh
Table 7. Conversion-Frequency Control Byte
DATA CONVERSION FREQUENCY (Hz) 0.0625 0.125 0.25 0.5 1 2 4 8 RFU AVERAGE SUPPLY CURRENT (A typ, at VCC = 3.3V) 30 33 35 48 70 128 225 425 --
*The HIGH and LOW temperature alarm flags stay high until cleared by POR or until status register is read.
Conversion Rate Byte
The conversion rate register (Table 7) programs the time interval between conversions in free-running autoconvert mode. This variable rate control reduces the supply current in portable-equipment applications. The conversion rate byte's POR state is 02h (0.25Hz). The MAX1619 looks only at the 3 LSB bits of this register, so the upper 5 bits are "don't care" bits, which should be set to zero. The conversion rate tolerance is 25% at any rate setting. Valid A/D conversion results for both channels are available one total conversion period (125ms nominal, 156ms maximum) after initiating a conversion, whether conversion is initiated via the RUN/STOP bit, hardware STBY pin, one-shot command, or initial power-up. Changing the conversion rate can also affect the delay until new results are available (Table 8).
Write-Once Protection
Write-once protection allows the host BIOS code to configure the MAX1619 in a particular way, and then protect that configuration against data corruption in the host that might cause spurious writes to the MAX1619. In particular, write protection allows a foolproof overtemperature override that forces the fan on 100% via OVERT independent of the host system. The write-protection bit (bit 4), once set high, can't be reset to low except by a hardware power-on reset. A SPOR (software POR) will not reset this bit.
Status Byte Functions
The status byte register (Table 6) indicates which (if any) temperature thresholds have been exceeded. This byte also indicates whether or not the ADC is converting and whether there is an open circuit in the remote diode DXP-DXN path. The status byte is cleared by any successful read of the status byte, unless the fault persists. The status of bit1 (OVER) follows the state of OVERT exactly. Note that the ALERT interrupt latch is not automatically cleared when the status flag bit is cleared. When autoconverting, if the THIGH and TLOW limits are close together, it's possible for both high-temp and lowtemp status bits to be set, depending on the amount of time between status read operations (especially when converting at the fastest rate). In these circumstances, it's best not to rely on the status bits to indicate reversals in long-term temperature changes. Instead, use a current temperature reading to establish the trend direction.
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Manufacturer and Device ID Codes
Two ROM registers provide manufacturer and device ID codes (Table 4). Reading the manufacturer ID returns 4Dh, which is the ASCII code "M" (for Maxim). Reading the device ID returns 04h, indicating a MAX1619 device. If READ WORD 16-bit SMBus protocol is employed (rather than the 8-bit READ BYTE), the least significant byte contains the data and the most significant byte contains 00h in both cases.
Slave Addresses
The MAX1619 appears to the SMBus as one device having a common address for both ADC channels. The device address can initially be set to one of nine different values by pin-strapping ADD0 and ADD1 so that more than one MAX1619 can reside on the same bus without address conflicts (Table 9).
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Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface MAX1619
Table 8. RLTS and RRTE Temperature Register Update Timing Chart
OPERATING MODE Autoconvert Autoconvert Autoconvert Autoconvert Autoconvert Autoconvert Autoconvert Autoconvert Autoconvert Autoconvert Autoconvert Hardware Standby Software Standby Software Standby CONVERSION INITIATED BY: Power-on reset One-shot command, while idling between automatic conversions One-shot command that occurs during a conversion Rate timer Rate timer Rate timer Rate timer Rate timer Rate timer Rate timer Rate timer STBY pin RUN/STOP bit One-shot command NEW CONVERSION FREQUENCY (CHANGED VIA WRITE TO WCRW) n/a (0.25Hz) n/a n/a 0.0625Hz 0.125Hz 0.25Hz 0.5Hz 1Hz 2Hz 4Hz 8Hz n/a n/a n/a TIME UNTIL RLTS AND RRTE ARE UPDATED 156ms max 156ms max When current conversion is complete (1-shot is ignored) 20sec 10sec 5sec 2.5sec 1.25sec 625ms 312.5ms 237.5ms 156ms 156ms 156ms
Table 9. POR Slave Address Decoding (ADD0 and ADD1)
ADD0 GND GND GND High-Z High-Z High-Z VCC VCC VCC ADD1 GND High-Z VCC GND High-Z VCC GND High-Z VCC ADDRESS 0011 000 0011 001 0011 010 0101 001 0101 010 0101 011 1001 100 1001 101 1001 110
Note: High-Z means that the pin is left unconnected and floating.
below 1.7V (typical, see Electrical Characteristics table). When power is first applied and VCC rises above 1.75V (typical), the logic blocks begin operating, although reads and writes at VCC levels below 3V are not recommended. A second VCC comparator, the ADC UVLO comparator, prevents the ADC from converting until there is sufficient headroom (VCC = 2.8V typical). The SPOR software POR command can force a power-on reset of the MAX1619 registers via the serial interface. Use the SEND BYTE protocol with COMMAND = FCh. This is most commonly used to reconfigure the slave address of the MAX1619 "on the fly," where external hardware has forced new states at the ADD0 and ADD1 address pins prior to the software POR. The new address takes effect less than 100s after the SPOR transmission stop condition. Power-Up Defaults: * Interrupt latch is cleared. * Address select pins are sampled. * ADC begins auto-converting at a 0.25Hz rate. * Command byte is set to 01h to facilitate quick remote Receive Byte queries. * THIGH and TLOW registers are set to +127C and -55C, respectively. * T MAX and T HYST are set to +100C and +95C, respectively. * OVERT polarity is active low.
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The address pin states are checked at POR and SPOR only, and the address data stays latched to reduce quiescent supply current due to the bias current needed for high-Z state detection. A new device address can be written using the Write Address Command FDh. The MAX1619 also responds to the SMBus Alert Response slave address (see the Alert Response Address section).
POR and UVLO
The MAX1619 has a volatile memory. To prevent ambiguous power-supply conditions from corrupting the data in memory and causing erratic behavior, a POR voltage detector monitors VCC and clears the memory if VCC falls
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Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface MAX1619
A tLOW
B tHIGH
C
D
E
F
G
H
I
J
K
SMBCLK
SMBDATA
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 MASTER H = LSB OF DATA CLOCKED INTO MASTER
tSU:STO I = ACKNOWLEDGE CLOCK PULSE J = STOP CONDITION K = NEW START CONDITION
tBUF
Figure 5. SMBus Write Timing Diagram
A
tLOW
B
tHIGH
C
D
E
F
G
H
I
J
K
L
M
SMBCLK
SMBDATA
tSU:STA
tHD:STA
tSU:DAT
tHD:DAT
tSU:STO tBUF
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
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO SLAVE H = LSB OF DATA CLOCKED INTO SLAVE I = SLAVE PULLS SMBDATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO MASTER K = ACKNOWLEDGE CLOCK PULSE L = STOP CONDITION, DATA EXECUTED BY SLAVE M = NEW START CONDITION
Figure 6. SMBus Read Timing Diagram
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Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface MAX1619
Listing 1. Pseudocode Example
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Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface MAX1619
Listing 1. Pseudocode Example (continued)
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Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface MAX1619
Listing 1. Pseudocode Example (continued)
Programming Example: Clock-Throttling Control for CPUs
Listing 1 gives an untested example of pseudocode for proportional temperature control of Intel mobile CPUs through a power-management microcontroller. This program consists of two main parts: an initialization routine and an interrupt handler. The initialization routine checks for SMBus communications problems and sets up the MAX1619 configuration and conversion rate. The interrupt handler responds to ALERT signals by reading the current temperature and setting a CPU clock duty factor proportional to that temperature. The relationship between clock duty and temperature is fixed in a lookup table contained in the microcontroller code.
Note: Thermal management decisions should be made based on the latest external temperature obtained from the MAX1619 rather than the value of the Status Byte. The MAX1619 responds very quickly to changes in its environment due to its sensitivity. High and low alarm conditions can exist at the same time in the Status Byte due to the MAX1619 correctly reporting environmental changes around it.
Chip Information
TRANSISTOR COUNT: 11,487
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Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface MAX1619
Package Information
QSOP.EPS
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.
20 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 (c) 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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