General Description The MAX6698 precision multichannel temperature sen- sor monitors its own temperature, the temperatures of three external diode-connected transistors, and the temperatures of three thermistors. All temperature channels have programmable alert thresholds. Channels 1, 4, 5, and 6 also have programmable over- temperature thresholds. When the measured tempera- ture of a channel exceeds the respective threshold, a status bit is set in one of the status registers. Two open- drain outputs, OVERT and ALERT, assert correspond- ing to these bits in the status register. The 2-wire serial interface supports the standard system management bus (SMBus™) protocols: write byte, read byte, send byte, and receive byte for reading the tem- perature data and programming the alarm thresholds. The MAX6698 is specified for an operating temperature range of -40°C to +125°C and is available in 16-pin QSOP and 16-pin TSSOP packages. Applications Desktop Computers Workstations Notebook Computers Servers Features ♦ Three Thermal-Diode Inputs and Three Thermistor Inputs ♦ Local Temperature Sensor ♦ 1°C Remote Temperature Accuracy (+60°C to +100°C) ♦ Temperature Monitoring Begins at POR for Fail- Safe System Protection ♦ ALERT and OVERT Outputs for Interrupts, Throttling, and Shutdown ♦ Small 16-Pin QSOP and 16-Pin TSSOP Packages ♦ 2-Wire SMBus Interface MAX6698 7-Channel Precision Remote-Diode, Thermistor, and Local Temperature Monitor ________________________________________________________________ Maxim Integrated Products 1 Ordering Information 16 +3.3V 15 14 13 12 11 10 9 1 2 3 4 5 6 R EX3 R THER3 7 8 GND SMBCLK SMBDATA DXN2 DXP2 DXN1 DXP1 V CC THER1 THER2 VREF THER3 DXN3 DXP3 MAX6698 ALERT OVERT R EX2 R THER2 R EX1 R THER1 Typical Application Circuit 19-3476; Rev 3; 8/07 For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. EVALUATION KIT AVAILABLE PART TEMP RANGE PIN- PACKAGE PKG CODE MAX6698EE_ _ -40°C to +125°C 16 QSOP E16-1 MAX6698UE_ _ -40°C to +125°C 16 TSSOP U16-1 SMBus is a trademark of Intel Corp. Pin Configuration appears at end of data sheet. *See the Slave Address section.
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7-Channel Precision Remote-Diode, Thermistor, and Local ...ELECTRICAL CHARACTERISTICS (continued) (VCC = +3.0V to +5.5V, TA = -40°C to +125°C, unless otherwise noted. Typical values
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General DescriptionThe MAX6698 precision multichannel temperature sen-sor monitors its own temperature, the temperatures ofthree external diode-connected transistors, and thetemperatures of three thermistors. All temperaturechannels have programmable alert thresholds.Channels 1, 4, 5, and 6 also have programmable over-temperature thresholds. When the measured tempera-ture of a channel exceeds the respective threshold, astatus bit is set in one of the status registers. Two open-drain outputs, OVERT and ALERT, assert correspond-ing to these bits in the status register.
The 2-wire serial interface supports the standard systemmanagement bus (SMBus™) protocols: write byte, readbyte, send byte, and receive byte for reading the tem-perature data and programming the alarm thresholds.
The MAX6698 is specified for an operating temperaturerange of -40°C to +125°C and is available in 16-pinQSOP and 16-pin TSSOP packages.
ApplicationsDesktop Computers Workstations
Notebook Computers Servers
Features♦ Three Thermal-Diode Inputs and Three Thermistor
Inputs
♦ Local Temperature Sensor
♦ 1°C Remote Temperature Accuracy (+60°C to+100°C)
♦ Temperature Monitoring Begins at POR for Fail-Safe System Protection
♦ ALERT and OVERT Outputs for Interrupts,Throttling, and Shutdown
♦ Small 16-Pin QSOP and 16-Pin TSSOP Packages
♦ 2-Wire SMBus Interface
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7-Channel Precision Remote-Diode, Thermistor,and Local Temperature Monitor
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functionaloperation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure toabsolute maximum rating conditions for extended periods may affect device reliability.
VCC, SCL, SDA, ALERT, OVERT to GND ................-0.3V to +6VDXP_ to GND..............................................-0.3V to (VCC + 0.3V)DXN_ to GND ........................................................-0.3V to +0.8VTHER_ to GND..........................................................-0.3V to +6VVREF to GND............................................................-0.3V to +6VSDA, ALERT, OVERT Current .............................-1mA to +50mADXN Current .......................................................................±1mAContinuous Power Dissipation (TA = +70°C)
ESD Protection (all pins, Human Body Model) ................±2000VOperating Temperature Range .........................-40°C to +125°CJunction Temperature ......................................................+150°CStorage Temperature Range .............................-60°C to +150°CLead Temperature (soldering, 10s) .................................+300°C
ELECTRICAL CHARACTERISTICS(VCC = +3.0V to +5.5V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25°C.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply Voltage VCC 3.0 5.5 V
Standby Supply Current ISS SMBus static 30 µA
Operating Current ICC During conversion 500 1000 µA
Channel 1 only 11Temperature Resolution
Other diode channels 8Bits
TA = TRJ = +60°C to +100°C -1.0 +1.0
TA = TRJ = 0°C to +125°C -3.0 +3.0Remote Temperature Accuracy VCC = 3.3V
DXN_ grounded,TRJ = TA = 0°C to +85°C
±2.5
oC
TA = +60°C to +100°C -2.5 +2.5Local Temperature Accuracy VCC = 3.3V
TA = 0°C to +125°C -3.5 +3.5oC
Supply Sensitivity of TemperatureAccuracy
±0.2 oC/V
Resistance cancellation on 95 125 156Remote Channel 1 ConversionTime
tCONV1Resistance cancellation off 190 250 312
ms
Remote Channels 2 Through 6Conversion Time
tCONV_ 95 125 156 ms
High level 80 100 120Remote-Diode Source Current IRJ
Low level 8 10 12µA
Undervoltage-Lockout Threshold UVLO Falling edge of VCC disables ADC 2.3 2.80 2.95 V
ELECTRICAL CHARACTERISTICS (continued)(VCC = +3.0V to +5.5V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25°C.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Reference-Load Regulation 0mA < IREF < 2mA 0.4 %
Reference-Supply Rejection 0.5 %/V
ALERT, OVERT
ISINK = 1mA 0.3Output Low Voltage VOL
ISINK = 6mA 0.5V
Output Leakage Current 1 µA
SMBus INTERFACE (SCL, SDA)
Logic-Input Low Voltage VIL 0.8 V
VCC = 3.0V 2.2 VLogic-Input High Voltage VIH
VCC = 5.0V 2.4 V
Input Leakage Current -1 +1 µA
Output Low Voltage VOL ISINK = 6mA 0.3 V
Input Capacitance CIN 5 pF
SMBus-COMPATIBLE TIMING (Figures 3 and 4) (Note 2)
Serial Clock Frequency fSCL (Note 3) 400 kHz
fSCL = 100kHz 4.7Bus Free Time Between STOPand START Condition
tBUFfSCL = 400kHz 1.6
µs
fSCL = 100kHz 4.7START Condition Setup Time
fSCL = 400kHz 0.6µs
90% of SCL to 90% of SDA, fSCL = 100kHz 0.6Repeat START Condition SetupTime
tSU:STA90% of SCL to 90% of SDA, fSCL = 400kHz 0.6
µs
START Condition Hold Time tHD:STA 10% of SDA to 90% of SCL 0.6 µs
90% of SCL to 90% of SDA, fSCL = 100kHz 4STOP Condition Setup Time tSU:STO
90% of SCL to 90% of SDA, fSCL = 400kHz 0.6µs
10% to 10%, fSCL = 100kHz 1.3Clock Low Period tLOW
10% to 10%, fSCL = 400kHz 1.3µs
Clock High Period tHIGH 90% to 90% 0.6 µs
fSCL = 100kHz 300Data Hold Time tHD:DAT
fSCL = 400kHz (Note 4) 900ns
fSCL = 100kHz 250Data Setup Time tSU:DAT
fSCL = 400kHz 100ns
fSCL = 100kHz 1Receive SCL/SDA Rise Time tR
fSCL = 400kHz 0.3µs
Receive SCL/SDA Fall Time tF 300 ns
Pulse Width of Spike Suppressed tSP 0 50 ns
SMBus Timeout tTIMEOUT SDA low period for interface reset 25 37 45 ms
Note 1: All parameters are tested at TA = +25°C. Specifications over temperature are guaranteed by design.Note 2: Timing specifications are guaranteed by design.Note 3: The serial interface resets when SCL is low for more than tTIMEOUT.Note 4: A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SCL’s falling edge.
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7-Channel Precision Remote-Diode, Thermistor,and Local Temperature Monitor
THERMISTOR ADC ERRORvs. POWER-SUPPLY NOISE FREQUENCY
MAX
6698
toc1
1
FREQUENCY (MHz)
TEM
PERA
TURE
ERR
OR (°
C)
1010.1
-4
-3
-2
-1
0
1
2
3
4
5
-50.01 100
100mVP-P
Pin Description
PIN NAME FUNCTION
1 DXP1Combined Current Source and A/D Positive Input for Channel 1 Remote Diode. Connect to the anodeof a remote-diode-connected temperature-sensing transistor. Leave floating or connect to VCC if noremote diode is used. Place a 2200pF capacitor between DXP1 and DXN1 for noise filtering.
2 DXN1Cathode Input for Channel 1 Remote Diode. Connect the cathode of the channel 1 remote-diode-connected transistor to DXN1.
3 DXP2Combined Current Source and A/D Positive Input for Channel 2 Remote Diode. Connect to the anodeof a remote-diode-connected temperature-sensing transistor. Leave floating or connect to VCC if noremote diode is used. Place a 2200pF capacitor between DXP2 and DXN2 for noise filtering.
4 DXN2Cathode Input for Channel 2 Remote Diode. Connect the cathode of the channel 2 remote-diode-connected transistor to DXN2.
5 DXP3Combined Current Source and A/D Positive Input for Channel 3 Remote Diode. Connect to the anodeof a remote-diode-connected temperature-sensing transistor. Leave floating or connect to VCC if noremote diode is used. Place a 2200pF capacitor between DXP3 and DXN3 for noise filtering.
6 DXN3Cathode Input for Channel 3 Remote Diode. Connect the cathode of the channel 1 remote-diode-connected transistor to DXN3.
7 THER3Thermistor Voltage Sense Input 3. Connect thermistor 3 between THER3 and ground and an externalresistor REXT3 between THER3 and VREF.
8 VREFThermistor Reference Voltage (1V Nominal). VREF is automatically enabled for a thermistorconversion, and is disabled for diode measurements.
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Detailed DescriptionThe MAX6698 is a precision multichannel temperaturemonitor that features one local, three remote thermaldiode temperature-sensing channels, and three ther-mistor voltage-sensing channels. All channels have aprogrammable alert threshold for each temperaturechannel and a programmable overtemperature thresh-old for channels 1, 4, 5, and 6 (see Figure 1).Communication with the MAX6698 is achieved throughthe SMBus serial interface and a dedicated alert(ALERT) pin. The alarm outputs, OVERT and ALERT,assert if the software-programmed temperature thresh-olds are exceeded. ALERT typically serves as an inter-rupt, while OVERT can be connected to a fan, systemshutdown, or other thermal-management circuitry.
Note that thermistor “temperature data” is really the volt-age across the fixed resistor, REXT, in series with thethermistor. This voltage is directly related to temperature,but the data is expressed in percentage of the referencevoltage not in °C.
ADC Conversion SequenceIn the default conversion mode, the MAX6698 starts theconversion sequence by measuring the temperature onthe channel 1 remote diode, followed by the channel 2,remote diode, channel 3 remote diode, and the localchannel. Then it measures thermistor channel 1, ther-mistor channel 2, and thermistor channel 3. The con-
version result for each active channel is stored in thecorresponding temperature data register.
In some systems, one of the remote thermal diodes maybe monitoring a location that experiences temperaturechanges that occur much more rapidly than in the otherchannels. If faster temperature changes must be moni-tored in one of the temperature channels, the MAX6698allows channel 1 to be monitored at a faster rate than theother channels. In this mode (set by writing a 1 to bit 4 ofthe configuration 1 register), measurements of channel 1alternate with measurements of the other channels. Thesequence becomes remote-diode channel 1, remote-diode channel 2, remote-diode channel 1, remote-diodechannel 3, remote-diode channel 1, etc. Note that thetime required to measure all seven channels is consider-ably greater in this mode than in the default mode.
Low-Power Standby ModeStandby mode reduces the supply current to less than15µA by disabling the internal ADC. Enter standby bysetting the STOP bit to 1 in the configuration 1 register.During standby, data is retained in memory, and theSMBus interface is active and listening for SMBus com-mands. The timeout is enabled if a start condition is rec-ognized on the SMBus. Activity on the SMBus causesthe supply current to increase. If a standby command isreceived while a conversion is in progress, the conver-sion cycle is interrupted, and the temperature registersare not updated. The previous data is not changed andremains available.
7-Channel Precision Remote-Diode, Thermistor,and Local Temperature Monitor
9 THER2Thermistor Voltage Sense Input 2. Connect thermistor 2 between THER2 and ground and an externalresistor REXT3 between THER2 and VREF.
10 THER1Thermistor Voltage Sense Input 1. Connect thermistor 1 between THER1 and ground and an externalresistor REXT3 between THER1 and VREF.
11 OVERTOvertemperature Active-Low, Open-Drain Output. OVERT asserts low when the temperature ofchannels 1, 4, 5, and 6 exceed the programmed threshold limit.
12 VCC Supply Voltage Input. Bypass to GND with a 0.1µF capacitor.
13 ALERTSMBus Alert (Interrupt), Active-Low, Open-Drain Output. ALERT asserts low when the temperature ofchannels 1, 4, 5, and 6 exceed programmed threshold limit.
14 SMBDATA SMBus Serial-Data Input/Output. Connect to a pullup resistor.
15 SMBCLK SMBus Serial-Clock Input. Connect to a pullup resistor.
16 GND Ground
SMBus Digital InterfaceFrom a software perspective, the MAX6698 appears asa series of 8-bit registers that contain temperature mea-surement data, alarm threshold values, and control bits.A standard SMBus-compatible 2-wire serial interface isused to read temperature data and write control bitsand alarm threshold data. The same SMBus slaveaddress also provides access to all functions.
The MAX6698 employs four standard SMBus protocols:write byte, read byte, send byte, and receive byte(Figure 2). The shorter receive byte protocol allowsquicker transfers, provided that the correct data regis-
ter was previously selected by a read byte instruction.Use caution with the shorter protocols in multimastersystems, since a second master could overwrite thecommand byte without informing the first master. Figure3 is the SMBus write timing diagram and Figure 4 is theSMBus read timing diagram.
The remote diode 1 measurement channel provides 11bits of data (1 LSB = 0.125°C). All other temperature-measurement channels provide 8 bits of temperaturedata (1 LSB = 1°C). The 8 most significant bits (MSBs)can be read from the local temperature, remote tem-perature, and thermistor registers. The remaining 3 bits
7-Channel Precision Remote-Diode, Thermistor,and Local Temperature Monitor
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for remote diode 1 can be read from the extended tem-perature register. If extended resolution is desired, theextended resolution register should be read first. Thisprevents the most significant bits from being overwrittenby new conversion results until they have been read. Ifthe most significant bits have not been read within anSMBus timeout period (nominally 25ms), normal updat-ing continues. Table 1 shows themistor voltage data for-mat. Table 2 shows the main temperature register (highbyte) data format. Table 3 shows the extended resolu-tion temperature register (low byte) data format.
Diode Fault DetectionIf a channel’s input DXP_ and DXN_ are left open, theMAX6698 detects a diode fault. An open diode faultdoes not cause either ALERT or OVERT to assert. A bitin the status register for the corresponding channel isset to 1 and the temperature data for the channel isstored as all 1s (FFh). It takes approximately 4ms forthe MAX6698 to detect a diode fault. Once a diode faultis detected, the MAX6698 goes to the next channel inthe conversion sequence. Depending on operatingconditions, a shorted diode may or may not causeALERT or OVERT to assert, so if a channel will not beused, disconnect its DXP and DXN inputs.
Alarm Threshold RegistersThere are 11 alarm threshold registers that store over-temperature ALERT and OVERT threshold values.Seven of these registers are dedicated to store onelocal alert temperature threshold limit, three remote alerttemperature threshold limits, and three thermistor volt-age threshold limits (see the ALERT Interrupt Mode sec-tion). The remaining four registers are dedicated toremote-diode channel 1, and three thermistor channels1, 2, and 3 to store overtemperature threshold limits(see the OVERT Overtemperature Alarm section).Access to these registers is provided through theSMBus interface.
7-Channel Precision Remote-Diode, Thermistor,and Local Temperature Monitor
7-Channel Precision Remote-Diode, Thermistor,and Local Temperature Monitor
SMBCLK
A = START CONDITIONB = MSB OF ADDRESS CLOCKED INTO SLAVEC = LSB OF ADDRESS CLOCKED INTO SLAVED = R/W BIT CLOCKED INTO SLAVE
A B C D E F G H I J
SMBDATA
tSU:STA tHD:STA
tLOW tHIGH
tSU:DATtSU:STO tBUF
L MK
E = SLAVE PULLS SMBDATA LINE LOWF = ACKNOWLEDGE BIT CLOCKED INTO MASTERG = MSB OF DATA CLOCKED INTO SLAVEH = LSB OF DATA CLOCKED INTO SLAVE
I = MASTER PULLS DATA LINE LOWJ = ACKNOWLEDGE CLOCKED INTO SLAVEK = ACKNOWLEDGE CLOCK PULSEL = STOP CONDITIONM = NEW START CONDITION
Figure 3. SMBus Write Timing Diagram
SMBCLK
A B C D E F G H I J K
SMBDATA
tSU:STA tHD:STA
tLOW tHIGH
tSU:DAT tHD:DAT tSU:STO tBUF
A = START CONDITIONB = MSB OF ADDRESS CLOCKED INTO SLAVEC = LSB OF ADDRESS CLOCKED INTO SLAVED = R/W BIT CLOCKED INTO SLAVEE = SLAVE PULLS SMBDATA LINE LOW
L M
F = ACKNOWLEDGE BIT CLOCKED INTO MASTERG = MSB OF DATA CLOCKED INTO MASTERH = LSB OF DATA CLOCKED INTO MASTERI = MASTER PULLS DATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO SLAVEK = ACKNOWLEDGE CLOCK PULSEL = STOP CONDITIONM = NEW START CONDITION
Figure 4. SMBus Read Timing Diagram
TEMP (°C) DIGITAL OUTPUT
>127 0111 1111
127 0111 1111
126 0111 1110
25 00011001
0.00 0000 0000
<0.00 0000 0000
Diode fault (open) 1111 1111
Diode fault (short) 1111 1111 or 1110 1110
Table 2. Main Temperature Register (HighByte) Data Format
8 ALERT Interrupt ModeAn ALERT interrupt occurs when the internal or externaltemperature reading exceeds a high-temperature limit(user programmable). The ALERT interrupt output sig-nal can be cleared by reading the status register(s)associated with the fault(s) or by successfully respond-ing to an alert response address transmission by themaster. In both cases, the alert is cleared but isreasserted at the end of the next conversion if the faultcondition still exists. The interrupt does not halt auto-matic conversions. The ALERT output is open drain sothat multiple devices can share a common interruptline. All ALERT interrupts can be masked using theconfiguration 3 register. The POR state of these regis-ters is shown in Table 4.
ALERT Response AddressThe SMBus alert response interrupt pointer providesquick fault identification for simple slave devices thatlack the complex logic needed to be a bus master.Upon receiving an interrupt signal, the host master canbroadcast a receive byte transmission to the alertresponse slave address (see the Slave Addresses sec-tion). Then, any slave device that generated an inter-rupt attempts to identify itself by putting its ownaddress on the bus.
The alert response can activate several different slavedevices simultaneously, similar to the I2C General Call.If more than one slave attempts to respond, bus arbitra-tion rules apply, and the device with the lower addresscode wins. The losing device does not generate anacknowledgment and continues to hold the ALERT linelow until cleared. (The conditions for clearing an alertvary depending on the type of slave device.)Successful completion of the alert response protocolclears the output latch. If the condition that caused thealert still exists, the MAX6698 reasserts the ALERTinterrupt at the end of the next conversion.
OVERT Overtemperature AlarmsThe MAX6698 has four overtemperature registers thatstore remote alarm threshold data for the OVERT out-put. OVERT is asserted when a channel’s measuredtemperature (voltage in the case of the thermistor chan-nels) is greater than the value stored in the correspond-ing threshold register. OVERT remains asserted untilthe temperature drops below the programmed thresh-old minus 4°C hysteresis for remote-diode channel 1, or
4 LSB hysteresis for thermistor channels 1, 2, and 3. Anovertemperature output can be used to activate a cool-ing fan, send a warning, initiate clock throttling, or trig-ger a system shutdown to prevent component damage.See Table 4 for the POR state of the overtemperaturethreshold registers.
Command Byte FunctionsThe 8-bit command byte register (Table 4) is the masterindex that points to the various other registers within theMAX6698. This register’s POR state is 0000 0000.
Configuration Bytes FunctionsThere are three read-write configuration registers(Tables 5, 6, 7) that can be used to control theMAX6698’s operation.
Configuration 1 RegisterThe configuration 1 register (Table 5) has several func-tions. Bit 7(MSB) is used to put the MAX6698 either insoftware standby mode (STOP) or continuous conver-sion mode. Bit 6 resets all registers to their power-onreset conditions and then clears itself. Bit 5 disablesthe SMBus timeout. Bit 4 enables more frequent con-versions on channel 1, as described in the ADCConversion Sequence section. Bit 3 enables resistancecancellation on channel 1. See the Series ResistanceCancellation section for more details. The remainingbits of the configuration 1 register are not used. ThePOR state of this register is 0000 0000 (00h).
Configuration 2 RegisterThe configuration 2 register functions are described inTable 6. Bits [6:0] are used to mask the ALERT interruptoutput. Bit 6 masks the local alert interrupt, bits 5through 3 mask the remote-diode ALERT interrupts, andbits 2 through 0 mask the thermistor alert interrupts. Thepower-up state of this register is 0000 0000 (00h).
Configuration 3 RegisterTable 7 describes the configuration 3 register. Bits 5, 4,3, and 0 mask the OVERT interrupt output for thermistorchannels 1, 2, and 3 and remote-diode channel 1. Theremaining bits, 7, 6, 2, and 1, are reserved. The power-up state of this register is 0000 0000 (00h).
7-Channel Precision Remote-Diode, Thermistor,and Local Temperature Monitor
09 00 R Read channel 1 remote-diode extended temperature register
Manufacturer ID 0A 4D R Read manufacturer ID
Device ID and Revision 0E 00 — —
Table 4. Command Byte Register Bit Assignment
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Status Registers FunctionsStatus registers 1, 2, and 3 (Tables 8, 9, 10) indicatewhich (if any) temperature thresholds have beenexceeded and if there is an open-circuit or short-circuitfault detected with the external sense junctions. Statusregister 1 indicates if the measured temperature hasexceeded the threshold limit set in the ALERT registersfor the local or remote-sensing diodes. Status register 2indicates if the measured temperature has exceededthe threshold limit set in the OVERT registers. Statusregister 3 indicates if there is a diode fault (open orshort) in any of the remote-sensing channels.
Bits in the alert status register clear by a successfulread, but set again after the next conversion unless thefault is corrected, either by a drop in the measured tem-perature or an increase in the threshold temperature.
The ALERT interrupt output follows the status flag bit.Once the ALERT output is asserted, it can be deassert-ed by either reading status register 1 or by successfullyresponding to an alert response address. In both cases,the alert is cleared even if the fault condition exists, butthe ALERT output reasserts at the end of the next con-version. Reading the status 2 register does not clear theOVERT interrupt output. To eliminate the fault condition,
7-Channel Precision Remote-Diode, Thermistor,and Local Temperature Monitor
7(MSB) STOP 0Standby Mode Control Bit. If STOP is set to logic 1, the MAX6698 stopsconverting and enters standby mode.
6 POR 0Reset Bit. Set to logic 1 to put the device into its power-on state. This bit is self-clearing.
5 TIMEOUT 0 Timeout Enable Bit. Set to logic 0 to enable SMBus timeout.
4 Fast remote 1 0Channel 1 Fast Conversion Bit. Set to logic 1 to enable fast conversion ofchannel 1.
3Resistancecancellation
0Resistance Cancellation Bit. When set to logic 1, the MAX6698 cancels seriesresistance in the channel 1 thermal diode.
2 Reserved 0 —
1 Reserved 0 —
0 Reserved 0 —
Table 5. Configuration 1 Register
BIT NAME POR STATE FUNCTION
7(MSB) Reserved 0 —
6 Mask Local ALERT 0 Local Alert Mask. Set to logic 1 to mask local channel ALERT.
5 Mask Thermistor 3ALERT 0 Thermistor 3 Alert Mask. Set to logic 1 to mask thermistor 3 ALERT.
4 Mask Thermistor 2ALERT 0 Thermistor 2 Alert Mask. Set to logic 1 to mask thermistor 2 ALERT.
3 Mask Thermistor 1ALERT 0 Thermistor 1 Alert Mask. Set to logic 1 to mask thermistor 1 ALERT.
2Mask Remote-Diode
3ALERT0
Remote-Diode 3 Alert Interrupt Mask. Set to logic 1 to mask remotediode 3 ALERT.
1Mask Remote-Diode
2ALERT0
Remote-Diode 2 Alert Interrupt Mask. Set to logic 1 to mask remotediode 2 ALERT.
0Mask Remote-Diode
2ALERT0
Remote-Diode 1 Alert Interrupt Mask. Set to logic 1 to mask remotediode 1 ALERT.
Table 6. Configuration 2 Register
either the measured value must drop below the thresh-old minus the hysteresis value (4°C or 4 LSBs), or thetrip threshold must be set at least 4°C (or 4 LSBs) abovethe current value.
Applications InformationRemote-Diode Selection
The MAX6698 directly measures the die temperature ofCPUs and other ICs that have on-chip temperature-sensing diodes (see the Typical Application Circuit) orit can measure the temperature of a discrete diode-connected transistor.
Effect of Ideality FactorThe accuracy of the remote temperature measurementsdepends on the ideality factor (n) of the remote “diode”(actually a transistor). The MAX6698 is optimized for n= 1.008. A thermal diode on the substrate of an IC isnormally a pnp with the base and emitter brought outthe collector (diode connection) grounded. DXP_ mustbe connected to the anode (emitter) and DXN_ must beconnected to the cathode (base) of this pnp. If a sensetransistor with an ideality factor other than 1.008 isused, the output data is different from the dataobtained with the optimum ideality factor. Fortunately,the difference is predictable. Assume a remote-diodesensor designed for a nominal ideality factor nNOMINALis used to measure the temperature of a diode with a
different ideality factor n1. The measured temperatureTM can be corrected using:
where temperature is measured in Kelvin andnNOMIMAL for the MAX6698 is 1.008. As an example,assume you want to use the MAX6698 with a CPU thathas an ideality factor of 1.002. If the diode has noseries resistance, the measured data is related to thereal temperature as follows:
For a real temperature of +85°C (358.15K), the mea-sured temperature is +82.87°C (356.02K), an error of-2.13°C.
Series Resistance CancellationSome thermal diodes on high-power ICs can haveexcessive series resistance, which can cause tempera-ture measurement errors with conventional remote tem-perature sensors. Channel 1 of the MAX6698 has aseries resistance cancellation feature (enabled by bit 3of the configuration 1 register) that eliminates the effectof diode series resistance. Set bit 3 to 1 if the seriesresistance is large enough to affect the accuracy of
7-Channel Precision Remote-Diode, Thermistor,and Local Temperature Monitor
BIT NAMEPOR
STATEFUNCTION
7(MSB) Reserved 0 —
6 Reserved 0 —
5Mask Thermistor 3
OVERT0 Thermistor 3 OVERT Mask Bit. Set to logic 1 to mask thermistor 3 OVERT.
4Mask Thermistor 2
OVERT0 Thermistor 2 OVERT Mask Bit. Set to logic 1 to mask thermistor 2 OVERT.
3Mask Thermistor 1
OVERT0 Thermistor 1 OVERT Mask Bit. Set to logic 1 to mask thermistor 1 OVERT.
2 Reserved 0 —
1 Reserved 0 —
0 Mask OVERT 1 0Channel 1 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 1OVERT.
Table 7. Configuration 3 Register
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channel 1. The series resistance cancellation functionincreases the conversion time for channel 1 by 125ms.This feature cancels the bulk resistance of the sensorand any other resistance in series (wire, contact resis-tance, etc.). The cancellation range is from 0 to 100Ω.
Discrete Remote DiodesWhen the remote-sensing diode is a discrete transistor,its collector and base must be connected together. Table11 lists examples of discrete transistors that are appropri-ate for use with the MAX6698. The transistor must be asmall-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 temperaturemust be greater than 0.25V at 10µA, and at the lowestexpected temperature, the forward voltage must be lessthan 0.95V at 100µA. Large power transistors must not beused. Also, ensure that the base resistance is less than10Ω. Tight specifications for forward current gain (50 < ß<150, for example) indicate that the manufacturer hasgood process controls and that the devices have consis-tent VBE characteristics. Manufacturers of discrete tran-sistors do not normally specify or guarantee idealityfactor. This is normally not a problem since good-qualitydiscrete transistors tend to have ideality factors that fallwithin a relatively narrow range. We have observed varia-
tions in remote temperature readings of less than ±2°Cwith a variety of discrete transistors. Still, it is good designpractice to verify good consistency of temperature read-ings with several discrete transistors from any manufac-turer under consideration.
Unused Diode ChannelsIf one or more of the remote diode channels is not need-ed, the DXP and DXN inputs for that channel shouldeither be unconnected, or the DXP input should be con-nected to VCC. The status register indicates a diode"fault" for this channel and the channel is ignored duringthe temperature-measurement sequence. It is also goodpractice to mask any unused channels immediately uponpower-up by setting the appropriate bits in theConfiguration 2 and Configuration 3 registers. This willprevent unused channels from causing ALERT# orOVERT# to assert.
Thermistor MeasurementsThe MAX6698 can use three external thermistors tomeasure temperature. A thermistor’s resistance variesas a function of temperature. A negative temperaturecoefficient (NTC) thermistor can be connected betweenthe thermistor input and ground, with a series resistor,REXT_, connected from the thermistor input to VREF.
7-Channel Precision Remote-Diode, Thermistor,and Local Temperature Monitor
6 Local ALERT 0Local Channel High-Alert Bit. This bit is set to logic 1 when the local temperatureexceeds the temperature threshold limit in the local ALERT high-limit register.
5 Thermistor 3 ALERT 0Thermistor 3 Alert Bit. This bit is set to logic 1 when the thermistor 3 voltageexceeds the threshold limit in the thermistor 3 ALERT high-limit register.
4 Thermistor 2 ALERT 0Thermistor 2 Alert Bit. This bit is set to logic 1 when the thermistor 2 voltageexceeds the threshold limit in the thermistor 2 ALERT high-limit register.
3 Thermistor 1 ALERT 0Thermistor 1 Alert Bit. This bit is set to logic 1 when the thermistor 1 voltageexceeds the threshold limit in the thermistor 1 ALERT high-limit register.
2Remote-Diode 3
ALERT0
Channel 3 Remote-Diode High-Alert Bit. This bit is set to logic 1 when thechannel 3 remote-diode temperature exceeds the programmed temperaturethreshold limit in the remote 3 ALERT high-limit register.
1Remote-Diode 2
ALERT0
Channel 2 Remote-Diode High-Alert Bit. This bit is set to logic 1 when thechannel 2 remote-diode temperature exceeds the temperature threshold limit inthe remote 2 ALERT high-limit register.
0Remote-Diode 1
ALERT0
Channel 1 Remote-Diode High-Alert Bit. This bit is set to logic 1 when thechannel 1 remote-diode temperature exceeds the temperature threshold limit inthe remote 1 ALERT high-limit register.
Table 8. Status 1 Register
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5 Thermistor 3 OVERT 0Thermistor 3 Overtemperature Status Bit. This bit is set to logic 1 when thethermistor 3 voltage exceeds the threshold limit in the thermistor 3 OVERThigh-limit register.
4 Thermistor 2 OVERT 0Thermistor 2 Overtemperature Status Bit. This bit is set to logic 1 when thethermistor 2 voltage exceeds the threshold limit in the thermistor 2 OVERThigh-limit register.
3 Thermistor 1 OVERT 0Thermistor 1 Overtemperature Status Bit. This bit is set to logic 1 when thethermistor 1 voltage exceeds the threshold limit in the thermistor 1 OVERThigh-limit register.
2 Reserved 0 —
1 Reserved 0 —
0 Remote 1 OVERT 0Channel 1 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1when the channel 1 remote-diode temperature exceeds the temperaturethreshold limit in the remote 1 OVERT high-limit register.
Table 9. Status 2 Register
BIT NAMEPOR
STATEFUNCTION
7(MSB) Reserved 0 —
6 Reserved 0 —
5 Reserved 0 —
4 Reserved 0 —
3 Diode fault 3 0Channel 3 Remote-Diode Fault Bit. This bit is set to 1 when DXP3 and DXN3are open circuit or when DXP3 is connected to VCC.
2 Diode fault 2 0Channel 2 Remote-Diode Fault Bit. This bit is set to 1 when DXP2 and DXN2are open circuit or when DXP2 is connected to VCC.
1 Diode fault 1 0Channel 1 Remote-Diode Fault Bit. This bit is set to 1 when DXP1 and DXN1are open circuit or when DXP1 is connected to VCC.
0 Reserved 0 —
Table 10. Status 3 Register
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VREF supplies a reference voltage (1V nominal) to biasthe thermistor/REXT_ voltage-divider. The voltageacross REXT is measured by the MAX6698’s ADC,resulting in a voltage that is directly proportional to tem-perature. The data in the thermistor registers gives thevoltage across REXT as a fraction of the reference volt-age (1LSB = 0.5% of VREF).
Because thermistors have nonlinear temperature-resis-tance functions, and because different thermistors havedifferent functions, it is important to understand therelationship between temperature, REXT, and the volt-age across REXT for a given thermistor. Table 13shows temperature vs. the thermistor channel data for aBetatherm 10k3A1 thermistor and REXT=1600Ω.
Thermal Mass and Self-HeatingWhen sensing local temperature, the MAX6698 mea-sures the temperature of the printed-circuit board(PCB) to which it is soldered. The leads provide a goodthermal path between the PCB traces and the die. As
with all IC temperature sensors, thermal conductivitybetween the die and the ambient air is poor by compar-ison, making air temperature measurements impracti-cal. Because the thermal mass of the PCB is far greaterthan that of the MAX6698, the device follows tempera-ture changes on the PCB with little or no perceivabledelay. When measuring the temperature of a CPU orother IC with an on-chip sense junction, thermal masshas virtually no effect; the measured temperature of thejunction tracks the actual temperature within a conver-sion cycle.
When measuring temperature with discrete remote tran-sistors, the best thermal response times are obtainedwith transistors in small packages (i.e., SOT23 orSC70). Take care to account for thermal gradientsbetween the heat source and the sensor, and ensurethat stray air currents across the sensor package donot interfere with measurement accuracy. Self-heatingdoes not significantly affect measurement accuracy.Remote-sensor self-heating due to the diode currentsource is negligible.
ADC Noise FilteringThe integrating ADC has good noise rejection for low-frequency signals such as power-supply hum. In envi-ronments with significant high-frequency EMI, connectan external 2200pF capacitor between DXP_ andDXN_. Larger capacitor values can be used for addedfiltering, but do not exceed 3300pF because it canintroduce errors due to the rise time of the switchedcurrent source. High-frequency noise reduction isneeded for high-accuracy remote measurements.Noise can be reduced with careful PCB layout as dis-cussed in the PCB Layout section.
PCB LayoutFollow these guidelines to reduce the measurementerror when measuring remote temperature:
1) Place the MAX6698 as close as is practical to theremote diode. In noisy environments, such as acomputer motherboard, this distance can be 4in to8in (typ). This length can be increased if the worstnoise sources are avoided. Noise sources includeCRTs, clock generators, memory buses, and PCIbuses.
2) Do not route the DXP-DXN lines next to the deflec-tion coils of a CRT. Also, do not route the tracesacross fast digital signals, which can easily intro-duce +30°C error, even with good filtering.
MANUFACTURER MODEL NO.
Central Semiconductor (USA) CMPT3904
Rohm Semiconductor (USA) SST3904
Samsung (Korea) KST3904-TF
Siemens (Germany) SMBT3904
Zetex (England) FMMT3904CT-ND
Table 11. Remote-Sensors TransistorManufacturers
Note: Discrete transistors must be diode connected (baseshorted to collector).
PART SMBus SLAVE ID PIN-PACKAGE
MAX6698EE34 0011 010 16 QSOP
MAX6698EE38 0011 100 16 QSOP
MAX6698EE99 1001 100 16 QSOP
MAX6698EE9C 1001 110 16 QSOP
MAX6698UE34 0011 010 16 TSSOP
MAX6698UE38 0011 100 16 TSSOP
MAX6698UE99 1001 100 16 TSSOP
MAX6698UE9C 1001 110 16 TSSOP
Table 12. Slave AddressTable 12 lists the MAX6698 slave addresses.
Slave Addresses
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7-Channel Precision Remote-Diode, Thermistor,and Local Temperature Monitor
3) Route the DXP and DXN traces in parallel and inclose proximity to each other. Each parallel pair oftraces should go to a remote diode. Route thesetraces away from any higher voltage traces, such as+12VDC. Leakage currents from PCB contaminationmust be dealt with carefully since a 20MΩ leakagepath from DXP to ground causes about +1°C error. Ifhigh-voltage traces are unavoidable, connect guardtraces to GND on either side of the DXP-DXN traces(Figure 5).
4) Route through as few vias and crossunders as pos-sible to minimize copper/solder thermocoupleeffects.
5) Use wide traces when practical.
6) When the power supply is noisy, add a resistor (upto 47Ω) in series with VCC.
Twisted-Pair and Shielded CablesUse a twisted-pair cable to connect the remote sensorfor remote-sensor distances longer than 8in or in verynoisy environments. Twisted-pair cable lengths can bebetween 6ft and 12ft before noise introduces excessiveerrors. For longer distances, the best solution is ashielded twisted pair like that used for audio micro-phones. For example, Belden #8451 works well for dis-
tances up to 100ft in a noisy environment. At thedevice, connect the twisted pair to DXP and DXN andthe shield to GND. Leave the shield unconnected at theremote sensor. For very long cable runs, the cable’sparasitic capacitance often provides noise filtering, sothe 2200pF capacitor can often be removed or reducedin value. Cable resistance also affects remote-sensoraccuracy. For every 1Ω of series resistance the error isapproximately +1/2°C.
10 mils
10 mils
10 mils
MINIMUM
10 mils
GND
DXP
DXN
GND
Figure 5. Recommended DXP-DXN PCB Traces
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7-Channel Precision Remote-Diode, Thermistor,and Local Temperature Monitor
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.)
QS
OP
.EP
S
F1
121-0055
PACKAGE OUTLINE, QSOP .150", .025" LEAD PITCH
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7-Channel Precision Remote-Diode, Thermistor,and Local Temperature Monitor
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses areimplied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
24 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
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.)