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19-2545; Rev 1; 10/02
Precision SMBus-Compatible Remote/Local Temperature Sensors with Overtemperature Alarms
General Description
The MAX6648/MAX6692 are precise, two-channel digital temperature sensors. They accurately measure the temperature of their own die and a remote PN junction, and report the temperature in digital form using a 2-wire serial interface. The remote PN junction is typically the emitter-base junction of a common-collector PNP on a CPU, FPGA, or ASIC. 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 to program the alarm thresholds. To enhance system reliability, the MAX6648/MAX6692 include an SMBus timeout. A fault queue prevents the ALERT and OVERT outputs from setting until a fault has been detected one, two, or three consecutive times (programmable). The MAX6648/MAX6692 provide two system alarms: ALERT and OVERT. ALERT asserts when any of four temperature conditions are violated: local overtemperature, remote overtemperature, local undertemperature, or remote undertemperature. OVERT asserts when the temperature rises above the value in either of the two OVERT limit registers. The OVERT output can be used to activate a cooling fan, or to trigger a system shutdown. Measurements can be done autonomously, with the conversion rate programmed by the user, or in a singleshot mode. The adjustable conversion rate allows the user to optimize supply current and temperature update rate to match system needs. Remote accuracy is 0.8C maximum error between +25C and +125C with no calibration needed. The MAX6648/MAX6692 operate from -55C to +125C, and measure temperatures between 0C and +125C. The MAX6648 is available in an 8-pin MAX package, and the MAX6692 is available in 8-pin MAX and SO packages.
Features
o Dual Channel: Measures Remote and Local Temperature o 0.125C Resolution o High Accuracy: 0.8C (max) from +25C to +125C (Remote), and 2C (max) from +60C to +100C (Local) o Two Alarm Outputs: ALERT and OVERT o Two Default OVERT Thresholds Available MAX6648: +110C MAX6692: +85C o Programmable Conversion Rate o SMBus-Compatible Interface o SMBus Timeout o Programmable Under/Overtemperature Alarm Thresholds
MAX6648/MAX6692
Ordering Information
PART TEMP RANGE PINMEASURED PACKAGE TEMP RANGE 0C to +125C 0C to +125C 0C to +125C
MAX6648MUA -55C to +125C 8 MAX MAX6692MUA -55C to +125C 8 MAX MAX6692MSA -55C to +125C 8 SO
Typical Operating Circuit
3.3V 0.1F 200
Applications
Desktop Computers Notebook Computers Servers Thin Clients Workstations Test and Measurement Multichip Modules
P 2200pF DXN VCC DXP
10k EACH SDA MAX6648 SCLK MAX6692 ALERT OVERT GND DATA CLOCK INTERRUPTED TO P TO FAN DRIVER OR SYSTEM SHUTDOWN
SMBus is a trademark of Intel Corp.
Pin Configuration and Functional Diagram appear at end of data sheet. 1
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Precision SMBus-Compatible Remote/Local Temperature Sensors with Overtemperature Alarms MAX6648/MAX6692
ABSOLUTE MAXIMUM RATINGS
All Voltages Referenced to GND VCC ...........................................................................-0.3V to +6V DXP.............................................................-0.3V to (VCC + 0.3V) DXN .......................................................................-0.3V to +0.8V SCLK, SDA, ALERT, OVERT.....................................-0.3V to +6V SDA, ALERT, OVERT Current .............................-1mA to +50mA DXN Current .......................................................................1mA Continuous Power Dissipation (TA = +70C) 8-Pin MAX (derate 5.9mW/C above +70C) .............471mW 8-Pin SO (derate 5.9mW/C above +70C)..................471mW ESD Protection (all pins, Human Body Model) ................2000V Junction Temperature ......................................................+150C Operating Temperature Range .........................-55C to +125C 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 = -55C to +125C, unless otherwise specified. Typical values are at VCC = 3.3V and TA = +85C.) (Note 1)
PARAMETER Supply Voltage Temperature Resolution VCC = 3.3V, TA = +85C Remote Temperature Error VCC = 3.3V, +60C TA +100C TRJ = +25C to +125C TRJ = +60C to +100C TRJ = 0C to +125C SYMBOL VCC CONDITIONS MIN 3.0 0.125 10 -0.8 -1.0 -1.6 -3.0 -2.0 -3.0 0.2 UVLO Falling edge of VCC disables ADC 2.4 2.7 90 VCC falling edge SMBus static During conversion 0.25 conversions per second 2 conversions per second tCONV From stop bit to conversion completion Standby mode IRJ High level Low level 80 8 100 10 95 -25 2.0 90 3.5 0.45 40 250 125 12 0.8 80 400 156 +25 100 120 12 2.95 +0.8 +1.0 C +1.6 +3.0 +2.0 +3.0 C C/V V mV V mV A mA A ms % nA A TYP MAX 5.5 UNITS V C Bits
VCC = 3.3V, +0C TRJ = 0C to +125C TA +100C Local Temperature Error Supply Sensitivity of Temperature Error Undervoltage Lockout (UVLO) Threshold UVLO Hysteresis Power-On-Reset (POR) Threshold POR Threshold Hysteresis Standby Supply Current Operating Current Average Operating Current Conversion Time Conversion Time Error DXP and DXN Leakage Current Remote-Diode Source Current VCC = 3.3V TA = +60C to +100C TA = 0C to +125C
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Precision SMBus-Compatible Remote/Local Temperature Sensors with Overtemperature Alarms
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 3.0V to 5.5V, TA = -55C to +125C, unless otherwise specified. Typical values are at VCC = 3.3V and TA = +85C.) (Note 1)
PARAMETER ALERT, OVERT Output Low Voltage Output High Leakage Current Logic Input Low Voltage Logic Input High Voltage Input Leakage Current Output Low-Sink Current Input Capacitance Serial Clock Frequency Bus Free Time Between STOP and START Condition START Condition Setup Time Repeat START Condition Setup Time START Condition Hold Time STOP Condition Setup Time Clock Low Period Clock High Period Data Setup Time Receive SCLK/SDA Rise Time Receive SCLK/SDA Fall Time Pulse Width of Spike Suppressed SMBus Timeout tSU:STA tHD:STA tSU:STO tLOW tHIGH tHD:DAT tR tF tSP tTIMEOUT SDA low period for interface reset 0 25 37 90% to 90% 10% of SDA to 90% of SCLK 90% of SCLK to 90% of SDA 10% to 10% 90% to 90% (Note 4) VIL VIH ILEAK ISINK CIN fSCLK tBUF (Note 3) 4.7 4.7 50 4 4 4.7 4 250 1 300 50 45 VCC = 3.0V VCC = 5.5V VIN = GND or VCC VOL = 0.6V 2.2 2.6 -1 6 5 100 +1 ISINK = 1mA ISINK = 4mA VOH = 5.5V 0.4 0.6 1 0.8 V A V V A mA pF kHz s s ns s s s s s s ns ns ms SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX6648/MAX6692
SMBus-COMPATIBLE INTERFACE (SCLK AND SDA)
SMBus-COMPATIBLE TIMING (Note 2)
Note 1: Note 2: Note 3: Note 4:
All parameters tested at a single temperature. Specifications over temperature are guaranteed by design. Timing specifications guaranteed by design. The serial interface resets when SCLK is low for more than tTIMEOUT. A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SCLK's falling edge.
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Precision SMBus-Compatible Remote/Local Temperature Sensors with Overtemperature Alarms MAX6648/MAX6692
Typical Operating Characteristics
(VCC = 3.3V, TA = +25C, unless otherwise noted.)
STANDBY SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX6648/92 toc01
OPERATING SUPPLY CURRENT vs. CONVERSION RATE
MAX6648/92 toc02
REMOTE TEMPERATURE ERROR vs. REMOTE-DIODE TEMPERATURE
MAX6648/92 toc03
4.0 STANDBY SUPPLY CURRENT (A)
600 OPERATING SUPPLY CURRENT (A) 500 400 300 200 100 0
2.5
3.6
TEMPERATURE ERROR (C)
1.5
0.5
3.2
-0.5
2.8
-1.5 TA = +85C FAIRCHILD 2N3906 -2.5 0.63 0.13 0.25 0.50 1.00 CONVERSION RATE (Hz) 2.00 4.00 0 25 50 75 100 125 TEMPERATURE (C)
2.4 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
LOCAL TEMPERATURE ERROR vs. DIE TEMPERATURE
MAX6648/92 toc04
TEMPERATURE ERROR vs. POWER-SUPPLY NOISE FREQUENCY
MAX6648/92 toc05
TEMPERATURE ERROR vs. COMMON-MODE NOISE FREQUENCY
8 TEMPERATURE ERROR (C) 7 6 5 4 3 2 1 0 -1 -2 LOCAL ERROR REMOTE ERROR VIN = AC-COUPLED TO DXN VIN = 100mVP-P
MAX6648/92 toc06
1.0 0.8 TEMPERATURE ERROR (C) 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 0 25 50 75 100
1.6 1.4 TEMPERATURE ERROR (C) 1.2 1.0 0.8 0.6 0.4 0.2 0 VIN = SQUARE WAVE APPLIED TO VCC WITH NO 0.1F VCC CAPACITOR 0.1 1 10 100 1k 10k REMOTE ERROR LOCAL ERROR
9
125
100k
1
10
100
1k
10k
100k
TEMPERATURE (C)
FREQUENCY (Hz)
FREQUENCY (Hz)
TEMPERATURE ERROR vs. DIFFERENTIAL-MODE NOISE FREQUENCY
MAX6648/92 toc07
TEMPERATURE ERROR vs. DXP-DXN CAPACITANCE
MAX6648/92 toc08
2.0 1.5 TEMPERATURE ERROR (C) 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 1 10 100 1k 10k VIN = 20mVP-P SQUARE WAVE APPLIED TO DXP-DXN
1 0 TEMPERATURE ERROR (C) -1 -2 -3 -4 -5 -6 0.100
100k
1.000
10.000
100.000
FREQUENCY (Hz)
DXP-DXN CAPACITANCE (nF)
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Precision SMBus-Compatible Remote/Local Temperature Sensors with Overtemperature Alarms
Pin Description
PIN 1 NAME VCC FUNCTION Supply Voltage Input, 3V to 5.5V. Bypass VCC to GND with a 0.1F capacitor. A 200 series resistor is recommended but not required for additional noise filtering. Combined Remote-Diode Current Source and A/D Positive Input for Remote-Diode Channel. DO NOT LEAVE DXP FLOATING; tie DXP to DXN if no remote diode is used. Place a 2200pF capacitor between DXP and DXN for noise filtering. Combined Remote-Diode Current Sink and A/D Negative Input. DXN is internally biased to one diode drop above ground. Overtemperature Alert/Interrupt Output, Open Drain. OVERT is logic low when the temperature is above the software-programmed threshold. Ground SMBus Alert (Interrupt) Output, Open Drain. ALERT asserts when temperature exceeds user-set limits (high or low temperature). ALERT stays asserted until acknowledged by either reading the status register or by successfully responding to an alert response address, provided that the fault condition no longer exists. See the ALERT Interrupts section. SMBus Serial-Data Input/Output, Open Drain SMBus Serial-Clock Input
MAX6648/MAX6692
2
DXP
3 4 5
DXN OVERT GND
6
ALERT
7 8
SDA SCLK
Detailed Description
The MAX6648/MAX6692 are temperature sensors designed to work in conjunction with a microprocessor or other intelligence in thermostatic, process-control, or monitoring applications. Communication with the MAX6648/MAX6692 occurs through the SMBus-compatible serial interface and dedicated alert pins. ALERT asserts if the measured local or remote temperature is greater than the software-programmed ALERT high limit or less than the ALERT low limit. ALERT also asserts if the remote-sensing diode pins are shorted or unconnected. The overtemperature alarm, OVERT, asserts if the software-programmed OVERT limit is exceeded. OVERT can be connected to fans, a system shutdown, a clock throttle control, or other thermalmanagement circuitry. The MAX6648/MAX6692 convert temperatures to digital data either at a programmed rate or in single conversions. Temperature data is represented as 10 bits plus sign, with the LSB equal to 0.125C. The "main" temperature data registers (at addresses 00h and 01h) are 8-bit registers that represent the data as 7 bits with the final MSB indicating the diode fault status (Table 1). The remaining 3 bits of temperature data are available in the "extended" registers at addresses 11h and 10h (Table 2).
ADC and Multiplexer
The averaging ADC integrates over a 60ms period (each channel, typically), with excellent noise rejection. The multiplexer automatically steers bias currents through the remote and local diodes. The ADC and associated circuitry measure each diode's forward voltage and compute the temperature based on this voltage. 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 ignore the results of the unused chan-
Table 1. Main Temperature Data Register Format (00h, 01h)
TEMP (C) 130 127 126 25 0 <0 -1 -25 Diode fault (short or open) DIGITAL OUTPUT 0 111 1111 0 111 1111 0 111 1111 0 001 1001 0 000 0000 0 000 0000 0 000 0000 0 000 0000 1 000 0000
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Precision SMBus-Compatible Remote/Local Temperature Sensors with Overtemperature Alarms MAX6648/MAX6692
nel. If the remote-diode channel is unused, connect DXP to DXN rather than leaving the pins open. The DXN input is biased to one VBE above ground by an internal diode to prepare the ADC 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 +0.5C (typ) error per ohm. The MAX6648/MAX6692 employ 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 when using the shorter protocols in multimaster systems, as a second master could overwrite the command byte without informing the first master. Temperature data can be read from the read internal temperature (00h) and read external temperature (01h) registers. The temperature data format for these registers is 7 bits plus 1 bit, indicating the diode fault status for each channel, with the LSB representing 1C (Table 1). The MSB is transmitted first. An additional 3 bits can be read from the read external extended temperature register (10h), which extends the data to 10 bits plus sign and the resolution to 0.125C per LSB (Table 2). An additional 3 bits can be read from the read internal extended temperature register (11h), which extends the data to 10 bits (plus 1 bit indicating the diode fault status) and the resolution to 0.125C per LSB (Table 2). When a conversion is complete, the main temperature register and the extended temperature register are updated simultaneously. Ensure that no conversions are completed between reading the main register and the extended register, so that both registers contain the result of the same conversion. To ensure valid extended data, read extended resolution temperature data using one of the following approaches: 1) Put the MAX6648/MAX6692 into standby mode by setting bit 6 of the configuration register to 1. Initiate a one-shot conversion using command byte 0Fh. When this conversion is complete, read the contents of the temperature data registers.
A/D Conversion Sequence
A conversion sequence consists of a local temperature measurement and a remote temperature measurement. Each time a conversion begins, whether initiated automatically in the free-running autonomous mode (RUN = 0) or by writing a one-shot command, both channels are converted, and the results of both measurements are available after the end of a conversion. A BUSY status bit in the status byte indicates that the device is performing a new conversion. The results of the previous conversion are always available, even if the ADC is busy.
Low-Power Standby Mode
Standby mode reduces the supply current to less than 10A by disabling the ADC and timing circuitry. Enter standby mode by setting the RUN bit to 1 in the configuration byte register (Table 6). All data is retained in memory, and the SMBus interface is active and listening for SMBus commands. Standby mode is not a shutdown mode. With activity on the SMBus, the device draws more supply current (see Typical Operating Characteristics). In standby mode, the MAX6648/MAX6692 can be forced to perform A/D conversions through the one-shot command, regardless of the RUN bit status. If a 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 a temperature register. The previous data is not changed and remains available. Supply-current drain during the 125ms conversion period is 500A (typ). Slowing down the conversion rate reduces the average supply current (see Typical Operating Characteristics). Between conversions, the conversion rate timer consumes about 25A of supply current. In standby mode, supply current drops to about 3A.
Table 2. Extended Resolution Temperature Register Data Format (10h, 11h)
FRACTIONAL TEMP (C) 0.000 0.125 0.250 0.375 0.500 0.625 0.750 0.875 DIGITAL OUTPUT 000X XXXX 001X XXXX 010X XXXX 011X XXXX 100X XXXX 101X XXXX 110X XXXX 111X XXXX
SMBus Digital Interface
From a software perspective, the MAX6648/MAX6692 appear as a set of byte-wide registers that contain temperature data, alarm threshold values, and control bits. A standard SMBus-compatible 2-wire serial interface is used to read temperature data and write control bits and alarm threshold data. These devices respond to the same SMBus slave address for access to all functions.
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Precision SMBus-Compatible Remote/Local Temperature Sensors with Overtemperature Alarms MAX6648/MAX6692
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
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 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 2. SMBus Write Timing Diagram
2) If the MAX6648/MAX6692 are in run mode, read the status byte. If the BUSY bit indicates that a conversion is in progress, wait until the conversion is complete (BUSY bit set to zero) before reading the temperature data. Following a conversion completion, immediately
read the contents of the temperature data registers. If no conversion is in progress, the data can be read within a few microseconds, which is a sufficiently short period of time to ensure that a new conversion cannot be completed until after the data has been read.
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Precision SMBus-Compatible Remote/Local Temperature Sensors with Overtemperature Alarms MAX6648/MAX6692
A tLOW B tHIGH C D E F G H I J K L M
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 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 3. SMBus Read Timing Diagram
Alarm Threshold Registers
Four registers store ALERT threshold values--one hightemperature (THIGH) and one low-temperature (TLOW) register each for the local and remote channels. If either measured temperature equals or exceeds the corresponding ALERT threshold value, the ALERT interrupt asserts. The power-on-reset (POR) state of both ALERT THIGH registers is full scale (0101 0101, or +85C). The POR state of both TLOW registers is 0000 0000, or 0C. Two additional registers store remote and local alarm threshold data corresponding to the OVERT output. The values stored in these registers are high-temperature thresholds. If either of the measured temperatures equals or exceeds the corresponding alarm threshold value, an OVERT output asserts. The POR state of the OVERT threshold is 0110 1110 or +110C for the MAX6648, and 0101 0101 or +85C for the MAX6692.
The ALERT interrupt output signal is latched and can be cleared only by either reading the status register or by successfully responding to an alert response address. In both cases, the alert is cleared only if the fault condition no longer exists. Asserting ALERT does not halt automatic conversion. The ALERT output pin is open drain, allowing multiple devices to share a common interrupt line. The MAX6648/MAX6692 respond to the SMBus alert response address, an interrupt pointer return-address feature (see the Alert Response Address section). Prior to taking corrective action, always check to ensure that an interrupt is valid by reading the current temperature.
Fault Queue Register
In some systems, it may be desirable to ignore a single temperature measurement that falls outside the ALERT limits. Bits 2 and 3 of the fault queue register (address 22h) determine the number of consecutive temperature faults necessary to set ALERT (see Tables 3 and 4).
Diode Fault Alarm
A continuity fault detector at DXP detects an open circuit between DXP and DXN, or a DXP short to VCC, GND, or DXN. If an open or short circuit exists, the external temperature register is loaded with 1000 0000. If the fault is an open-circuit fault bit 2 (OPEN) of the status byte, it is set to 1 and the ALERT condition is activated at the end of the conversion. Immediately after POR, the status register indicates that no fault is present. If a fault is present upon power-up, the fault is not indicated until the end of the first conversion.
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). Following such a broadcast, any slave device that generated an interrupt attempts to identify itself by putting its own address on the bus. 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
I 2C is a trademark of Philips Corp.
ALERT Interrupts
The ALERT interrupt occurs when the internal or external temperature reading exceeds a high- or low-temperature limit (user programmed) or when the remote diode is disconnected (for continuity fault detection).
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Precision SMBus-Compatible Remote/Local Temperature Sensors with Overtemperature Alarms MAX6648/MAX6692
Table 3. Fault Queue Register Bit Definition (22h)
BIT 7 6 to 3 2 1 0 NAME RFU RFU FQ1 FQ0 RFU POR STATE 1 0 0 0 0 FUNCTION Reserved. Always write 1 to this bit. Reserved. Always write zero to this bit. Fault queue-length control bit (see Table 4). Fault queue-length control bit (see Table 4). Reserved. Always write zero to this bit.
Table 4. Fault Queue Length Bit Definition
FQ1 0 0 1 1 FQ0 0 1 1 0 FAULT QUEUE LENGTH (SAMPLES) 1 2 3 --
mode (RUN bit = 1), a new conversion begins, after which the device returns to standby mode. If a one-shot conversion is in progress when a one-shot command is received, the command is ignored. If a one-shot command is received in autonomous mode (RUN bit = 0) between conversions, a new conversion begins, the conversion rate timer is reset, and the next automatic conversion takes place after a full delay elapses.
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 cleared. (The conditions for clearing an ALERT vary, depending on the type of slave device). Successful completion of the read alert response protocol clears the interrupt latch, provided the condition that caused the alert no longer exists.
Configuration Byte Functions
The configuration byte register (Table 6) is a read-write register with several functions. Bit 7 is used to mask (disable) interrupts. Bit 6 puts the MAX6648/MAX6692 into standby mode (STOP) or autonomous (RUN) mode.
Status Byte Functions
The status byte register (Table 7) indicates which (if any) temperature thresholds have been exceeded. This byte also indicates whether the ADC is converting and whether there is an open-circuit fault detected in the external sense junction. After POR, the normal state of all flag bits is zero, assuming no alarm conditions are present. The status byte is cleared by any successful read of the status byte, after a conversion is complete and the fault no longer exists. Note that the ALERT interrupt latch is not automatically cleared when the status flag bit indicating the ALERT is cleared. The fault condition must be eliminated before the ALERT output can be cleared. When autoconverting, if the THIGH and TLOW limits are close together, it is possible for both high-temp and low-temp 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 is 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.
OVERT Overtemperature Alarm/Warning Outputs
OVERT asserts when the temperature rises to a value stored in one of the OVERT limit registers (19h, 20h). It deasserts when the temperature drops below the stored limit, minus hysteresis. OVERT can be used to activate a cooling fan, send a warning, invoke clock throttling, or trigger a system shutdown to prevent component damage.
Command Byte Functions
The 8-bit command byte register (Table 5) is the master index that points to the various other registers within the MAX6648/MAX6692. The register's POR state is 0000 0000, so a receive byte transmission (a protocol that lacks the command byte) that occurs immediately after POR, returns the current local temperature data. The MAX6648/MAX6692 incorporate collision avoidance so that completely asynchronous operation is allowed between SMBus operations and temperature conversions.
Conversion Rate Byte
The conversion rate register (Table 8) programs the time interval between conversions in free-running autonomous mode (RUN = 0). This variable rate control can be used to reduce the supply current in portable9
One-Shot
The one-shot command immediately forces a new conversion cycle to begin. If the one-shot command is received while the MAX6648/MAX6692 are in standby
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Precision SMBus-Compatible Remote/Local Temperature Sensors with Overtemperature Alarms MAX6648/MAX6692
Table 5. Command-Byte Bit Assignments
REGISTER RLTS RRTE RSL RCL RCRA RLHN RLLI RRHI RRLS WCA WCRW WLHO WLLM WRHA WRLN OSHT REET RIET RWOE RWOI HYS QUEUE -- -- ADDRESS 00h 01h 02h 03h 04h 05h 06h 07h 08h 09h 0Ah 0Bh 0Ch 0Dh 0Eh 0Fh 10h 11h 19h 20h 21h 22h FEh FFh POR STATE 0000 0000 0000 0000 N/A 0000 0000 0000 0111 0101 0101 0000 0000 0101 0101 0000 0000 N/A N/A N/A N/A N/A N/A N/A 0000 0000 0000 0000 0110 1110 0101 0101 0101 0101 0000 1010 1000 0000 0100 1101 0101 1001 0C 0C -- -- -- +85C 0C +85C 0C -- -- -- -- -- -- -- 0C 0C +110C +85C +85C 10C -- -- -- FUNCTION Read local (internal) temperature Read remote (external) temperature Read status byte Read configuration byte Read conversion rate byte Read local (internal) ALERT high limit Read local (internal) ALERT low limit Read remote (external) ALERT high limit Read remote (external) ALERT low limit Write configuration byte Write conversion rate byte Write local (internal) ALERT high limit Write local (internal) ALERT low limit Write remote (external) ALERT high limit Write remote (external) ALERT low limit One-shot Read remote (external) extended temperature Read local (internal) extended temperature Read/write remote (external) OVERT limit (MAX6648) Read/write remote (external) OVERT limit (MAX6692) Read/write local (internal) OVERT limit Overtemperature hysteresis Fault queue Read manufacture ID Read revision ID
Table 6. Configuration-Byte Bit Assignments (03h)
BIT 7 (MSB) 6 5 to 0 NAME MASK RUN RFU POR STATE 0 0 0 FUNCTION Masks ALERT interrupts when set to 1. Standby mode control bit; if set to 1, standby mode is initiated. Reserved.
equipment applications. The conversion rate byte's POR state is 07h or 4Hz. The MAX6648/MAX6692 look only at the 3 LSBs 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 time (125ms nominal, 156ms maximum) after initiating a conversion, whether conversion is initiated through the RUN bit, one-shot com10
mand, or initial power-up. Changing the conversion rate can also affect the delay until new results are available.
Slave Addresses
The MAX6648/MAX6692 have a fixed address of 1001 100. The MAX6648/MAX6692 also respond to the SMBus alert response slave address (see the Alert Response Address section).
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Precision SMBus-Compatible Remote/Local Temperature Sensors with Overtemperature Alarms MAX6648/MAX6692
Table 7. Status Register Bit Assignments (02h)
BIT 7 (MSB) 6 5 4 3 2 1 0 NAME BUSY LHIGH LLOW RHIGH RLOW FAULT EOT IOT POR STATE 0 0 0 0 0 0 0 0 A/D is busy converting when 1. Local (internal) high-temperature alarm has tripped when 1; cleared by POR or readout of the status byte if the fault condition no longer exists. Local (internal) low-temperature alarm has tripped when 1; cleared by POR or readout of the status byte if the fault condition no longer exists. Remote (external) high-temperature alarm has tripped when 1; cleared by POR or readout of the status byte if the fault condition no longer exists. Remote (external) low-temperature alarm has tripped when 1; cleared by POR or readout of the status byte if the fault condition no longer exists. A 1 indicates DXN and DXP are either shorted or open; cleared by POR or readout of the status byte if the fault condition no longer exists. A 1 indicates the remote (external) junction temperature exceeds the external OVERT threshold. A 1 indicates the local (internal) junction temperature exceeds the internal OVERT threshold. FUNCTION
POR and UVLO
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 below 2.0V (typ). When power is first applied and VCC rises above 2.0V (typ), 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 typ).
Table 8. Conversion-Rate Control Byte (04h)
DATA 00h 01h 02h 03h 04h 05h 06h 07h 08h-FFh CONVERSION RATE (Hz) 0.0625 0.125 0.25 0.5 1 2 4 4 Reserved
Power-Up Defaults
Power-up defaults include: * Interrupt latch is cleared. * ADC begins autoconverting at a 4Hz rate. * Command byte is set to 00h to facilitate quick local temperature receive byte queries. * Local (internal) THIGH limit set to +85C. * Local (internal) TLOW limit set to 0C. * Remote (external) THIGH limit set to +85C. * Remote (external) TLOW limit set to 0C. * OVERT internal limit is set to +85C; every external limit is set to +110C (MAX6648). * OVERT limits are set to +85C (MAX6692).
Applications Information
Remote-Diode Selection
The MAX6648/MAX6692 can directly measure the die temperature of CPUs and other ICs that have on-board temperature-sensing diodes (see Typical Operating Circuit), or they can measure the temperature of a discrete diode-connected transistor.
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Precision SMBus-Compatible Remote/Local Temperature Sensors with Overtemperature Alarms MAX6648/MAX6692
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 MAX6648/MAX6692 are 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 MAX6648/MAX6692 is 1.008. As an example, assume you want to use the MAX6648/MAX6692 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) 1.002 n1
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 and base connected together. Table 9 lists examples of discrete transistors that are appropriate for use with the MAX6648/ MAX6692.
Table 9. Remote-Sensor Transistor Manufacturers
MANUFACTURER Central Semiconductor (USA) Rohm Semiconductor (USA) Samsung (Korea) Siemens (Germany) MODEL NO. CMPT3904 SST3904 KST3904-TF SMBT3904
For a real temperature of +85C (358.15 K), the measured temperature is +82.91C (356.02 K), 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 Since 1C corresponds to 198.6V, series resistance contributes a temperature offset of: = 0.453 C V 198.6 C Assume that the diode being measured has a series 90 V
Note: Transistors must be diode connected (base shorted to collector).
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 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 < <150, for example) indicate that the manufacturer has good process controls and that the devices have consistent VBE characteristics.
ADC Noise Filtering
The integrating ADC used has good noise rejection for low-frequency signals such as 60Hz/120Hz power-supply hum. In noisy environments, high-frequency noise reduction is needed for high-accuracy remote mea-
Intel and Pentium are registered trademarks of Intel Corp. 12
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Precision SMBus-Compatible Remote/Local Temperature Sensors with Overtemperature Alarms
GND 10MILS 10MILS DXP MINIMUM 10MILS DXN 10MILS GND
Figure 4. Recommended DXP-DXN PC Traces
surements. The noise can be reduced with careful PC board layout and proper external noise filtering. High-frequency EMI is best filtered at DXP and DXN with an external 2200pF capacitor. Larger capacitor values can be used for added filtering, but do not exceed 3300pF because larger values can introduce errors due to the rise time of the switched current source.
exhibits 3V/C, and takes about 200V of voltage error at DXP-DXN to cause a 1C measurement error. Adding a few thermocouples causes a negligible error. 6) Use wide traces. Narrow traces are more inductive and tend to pick up radiated noise. The 10mil widths and spacing recommended in Figure 4 are not absolutely necessary, as they offer only a minor improvement in leakage and noise over narrow traces. Use wider traces when practical. 7) Add a 200 resistor in series with VCC for best noise filtering (see Typical Operating Circuit). 8) Copper cannot be used as an EMI shield; 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.
MAX6648/MAX6692
Twisted-Pair and Shielded Cables
Use a twisted-pair cable to connect the remote sensor for remote-sensor distance longer than 8in, or in very noisy environments. Twisted-pair cable lengths can be between 6ft and 12ft before noise introduces excessive errors. 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. At the device, connect the twisted pair to DXP and DXN and the shield to GND. Leave the shield unconnected at the remote sensor. 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. For every 1 of series resistance, the error is approximately 0.5C.
PC Board Layout
Follow these guidelines to reduce the measurement error of the temperature sensors: 1) Place the MAX6648/MAX6692 as close as is practical to the remote diode. In noisy environments, such as a computer motherboard, this distance can be 4in to 8in (typ). This length can be increased if the worst noise sources are avoided. Noise sources include CRTs, clock generators, memory buses, and ISA/PCI buses. 2) Do not route the DXP-DXN lines next to the deflection coils of a CRT. Also, do not route the traces across fast digital signals, which can easily introduce 30C error, even with good filtering. 3) Route the DXP and DXN traces in parallel and in close proximity to each other, away from any higher voltage traces, such as 12VDC. Leakage currents from PC board contamination must be dealt with carefully since a 20M leakage path from DXP to ground causes about 1C error. If high-voltage traces are unavoidable, connect guard traces to GND on either side of the DXP-DXN traces (Figure 4). 4) Route through as few vias and crossunders as possible to minimize copper/solder thermocouple effects. 5) When introducing a thermocouple, make sure that both the DXP and the DXN paths have matching thermocouples. A copper-solder thermocouple
Thermal Mass and Self-Heating
When sensing local temperature, these devices are intended to measure the temperature of the PC board to which they are soldered. The leads provide a good thermal path between the PC board traces and the die. Thermal conductivity between the die and the ambient air is poor by comparison, making air temperature measurements impractical. Because the thermal mass of the PC board is far greater than that of the MAX6648/ MAX6692, the devices follow temperature changes on the PC board with little or no perceivable delay. When measuring the temperature of a CPU or other IC with an on-chip sense junction, thermal mass has virtually no effect; the measured temperature of the junction tracks the actual temperature within a conversion cycle.
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Precision SMBus-Compatible Remote/Local Temperature Sensors with Overtemperature Alarms MAX6648/MAX6692
Functional Diagram
VCC
MAX6648 MAX6692
2 DXP DXN MUX REMOTE ADC LOCAL DIODE FAULT ALERT S Q R REGISTER BANK COMMAND BYTE OVERT S Q R REMOTE TEMPERATURE LOCAL TEMPERATURE ALERT THRESHOLD ALERT RESPONSE ADDRESS OVERT THRESHOLD ADDRESS DECODER 7 SMBus 8 8 READ WRITE SMBDATA SMBCLK
CONTROL LOGIC
When measuring temperature with discrete remote sensors, smaller packages, such as SOT23s, yield the best thermal response times. 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 worst-case error occurs when autoconverting at the fastest rate and simultaneously sinking maximum current
at the ALERT output. For example, with VCC = 5.0V, at a 4Hz conversion rate and with ALERT sinking 1mA, the typical power dissipation is: 5.0V x 500A + 0.4V x 1mA = 2.9mW
oJ-A for the 8-pin MAX package is about +221C/W,
so assuming no copper PC board heat sinking, the resulting temperature rise is: T = 2.9mW x (+221C/W) = +0.6409C Even under nearly worst-case conditions, it is difficult to introduce a significant self-heating error.
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Precision SMBus-Compatible Remote/Local Temperature Sensors with Overtemperature Alarms MAX6648/MAX6692
Pin Configuration
TOP VIEW
VCC DXP DXN OVERT 1 2 3 4 8 SCLK SDA ALERT GND
Chip Information
TRANSISTOR COUNT: 14,764 PROCESS: BiCMOS
MAX6648 MAX6692 MAX/SO*
7 6 5
*SO PACKAGE AVAILABLE FOR MAX6692 ONLY.
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Precision SMBus-Compatible Remote/Local Temperature Sensors with Overtemperature Alarms MAX6648/MAX6692
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.)
8LUMAXD.EPS
8
4X S
8
INCHES DIM A A1 A2 b c D e E H MIN 0.002 0.030 MAX 0.043 0.006 0.037
MILLIMETERS MAX MIN 0.05 0.75 1.10 0.15 0.95
y 0.500.1 0.60.1
E
H
1
0.60.1
1
D
L
S
BOTTOM VIEW
0.010 0.014 0.005 0.007 0.116 0.120 0.0256 BSC 0.116 0.120 0.188 0.198 0.016 0.026 0 6 0.0207 BSC
0.25 0.36 0.13 0.18 2.95 3.05 0.65 BSC 2.95 3.05 4.78 5.03 0.41 0.66 0 6 0.5250 BSC
TOP VIEW
A2
A1
A
e
c b L
SIDE VIEW
FRONT VIEW
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE, 8L uMAX/uSOP
APPROVAL DOCUMENT CONTROL NO. REV.
21-0036
J
1 1
16
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Precision SMBus-Compatible Remote/Local Temperature Sensors with Overtemperature Alarms
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.)
9LUCSP, 3x3.EPS
MAX6648/MAX6692
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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