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19-4097; Rev 0; 4/08
5-Channel Precision Temperature Monitor with Beta Compensation
General Description
The MAX6694 precision multichannel temperature sensor monitors its own temperature and the temperatures of up to four external diode-connected transistors. All temperature channels have programmable alert thresholds. Channels 1 and 4 also have programmable overtemperature thresholds. When the measured temperature 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 corresponding to these bits in the status register. The 2-wire serial interface supports the standard system management bus (SMBusTM) protocols: write byte, read byte, send byte, and receive byte for reading the temperature data and programming the alarm thresholds. The MAX6694 is specified for a -40C to +125C operating temperature range and is available in 16-pin TSSOP and 5mm x 5mm thin QFN packages. o Four Thermal-Diode Inputs o Beta Compensation (Channel 1) o Local Temperature Sensor o 1.5C Remote Temperature Accuracy (+60C to +100C) o Temperature Monitoring Begins at POR for FailSafe System Protection o ALERT and OVERT Outputs for Interrupts, Throttling, and Shutdown o STBY Input for Hardware Standby Mode o Small, 16-Pin TSSOP and TQFN Packages o 2-Wire SMBus Interface
Features
MAX6694
Applications
Desktop Computers Notebook Computers Workstations Servers
SMBus is a trademark of Intel Corp. Pin Configurations appear at end of data sheet.
PART MAX6694UE9A+
Ordering Information
TEMP RANGE -40C to +125C PIN-PACKAGE 16 TSSOP 16 TQFN-EP*
MAX6694TE9A+ -40C to +125C +Denotes a lead-free package. *EP = Exposed pad. Note: Slave address is 1001 101.
Typical Application Circuit
+3.3V
CPU 1 100pF 2 3 100pF 4 5 100pF 6 7 100pF 8 DXN4 STBY 9 DXN3 DXP4 OVERT 11 N.C. 10 DXN2 DXP3 ALERT 13 VCC 12 0.1F DXN1 DXP2 SMBCLK 15 DXP1 GND 16
4.7k EACH CLK DATA INTERRUPT TO P
MAX6694 SMBDATA 14
TO SYSTEM SHUTDOWN
________________________________________________________________ Maxim Integrated Products
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5-Channel Precision Temperature Monitor with Beta Compensation MAX6694
ABSOLUTE MAXIMUM RATINGS
VCC, SMBCLK, SMBDATA, ALERT, OVERT, STBY to GND ....................................................-0.3V to +6.0V DXP_ to GND..............................................-0.3V to (VCC + 0.3V) DXN_ to GND ........................................................-0.3V to +0.8V SMBDATA, ALERT, OVERT Current....................-1mA to +50mA DXIV_ Current .....................................................................1mA Continuous Power Dissipation (TA = +70C) 16-Pin TQFN, 5mm x 5mm (derate 33.3mW/C above +70C)............................2666.7mW 16-Pin TSSOP (derate 11.1mW/C above +70C) ............................888.9mW Junction-to-Case Thermal Resistance (JC) (Note 1) 16-Pin TQFN...................................................................2C/W 16-Pin TSSOP...............................................................27C/W Junction-to-Ambient Thermal Resistance (JA) (Note 1) 16-Pin TQFN.................................................................30C/W 16-Pin TSSOP...............................................................90C/W ESD Protection (all pins, Human Body Model) ....................2kV Operating Temperature Range .........................-40C to +125C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a fourlayer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.
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 +3.6V, VSTBY = VCC, TA = -40C to +125C, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25C.) (Note 2)
PARAMETER Supply Voltage Software Standby Supply Current Operating Current Temperature Resolution 3 Temperature Accuracy (Remote Channel 1) 3 Temperature Accuracy (Remote Channels 2-6) 3 Temperature Accuracy (Local) 6 Temperature Accuracy (Remote Channel 1) 6 Temperature Accuracy (Remote Channels 2-6) 6 Temperature Accuracy (Local) Supply Sensitivity of Temperature Accuracy Remote Channel 1 Conversion Time Remote Channels 2, 3, 4 Conversion Time tCONV1 tCONV_ 190 95 SYMBOL VCC ISS ICC SMBus static During conversion (Note 3) Channel 1 only Other diode channels VCC = 3.3V, TA = TRJ = +60C to +100C = 0.5 TA = TRJ = 0C to +125C TA = TRJ = +60C to +100C VCC = 3.3V TA = TRJ = 0C to +125C VCC = 3.3V TA = +60C to +100C TA = 0C to +125C -1.5 -2.375 -2 -2.5 -2 -2.5 -3 -4 -3 -3.5 -2.5 -3 0.2 250 125 312 156 CONDITIONS MIN 3.0 3 500 11 8 +1.5 +2.375 +2 +2.5 +2 +2.5 +3 +4 +3 +3.5 +2.5 +3
o
TYP
MAX 3.6 10 2000
UNITS V A A Bits C C C C C C C/V ms ms
VCC = 3.3V, TA = TRJ = +60C to +100C = 0.5 TA = TRJ = 0C to +125C VCC = 3.3V VCC = 3.3V TA = TRJ = +60C to +100C TA = TRJ = 0C to +125C TA = +60C to +100C TA = 0C to +125C
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5-Channel Precision Temperature Monitor with Beta Compensation
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.0V to +3.6V, VSTBY = VCC, TA = -40C to +125C, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25C.) (Note 2)
PARAMETER SYMBOL CONDITIONS High level, channel 1 Remote-Diode Source Current IRJ Low level, channel 1 High level, channels 2, 3, 4 Low level, channels 2, 3, 4 Undervoltage-Lockout Threshold Undervoltage-Lockout Hysteresis Power-On-Reset (POR) Threshold POR Threshold Hysteresis ALERT, OVERT Output Low Voltage Output Leakage Current SMBus INTERFACE (SMBCLK, SMBDATA), STBY Logic Input Low Voltage Logic Input High Voltage Input Leakage Current Output Low Voltage Input Capacitance Serial-Clock Frequency Bus Free Time Between STOP and START Condition START Condition Setup Time VOL CIN fSMBCLK tBUF (Note 5) fSMBCLK = 100kHz fSMBCLK = 400kHz fSMBCLK = 100kHz fSMBCLK = 400kHz 90% of SMBCLK to 90% of SMBDATA, fSMBCLK = 100kHz 90% of SMBCLK to 90% of SMBDATA, fSMBCLK = 400kHz 10% of SMBDATA to 90% of SMBCLK 90% of SMBCLK to 90% of SMBDATA, fSMBCLK = 100kHz 90% of SMBCLK to 90% of SMBDATA, fSMBCLK = 400kHz 10% to 10%, fSMBCLK = 100kHz 10% to 10%, fSMBCLK = 400kHz 90% to 90% fSMBCLK = 100kHz fSMBCLK = 400kHz (Note 6) 4.7 1.6 4.7 0.6 0.6 s 0.6 0.6 4 s 0.6 1.3 1.3 0.6 300 900 s s ns s ISINK = 6mA 5 400 VIL VIH VCC = 3.0V 2.2 -1 +1 0.3 0.8 V V A V pF kHz s s VOL ISINK = 1mA ISINK = 6mA 0.3 0.5 1 V A VCC falling edge 1.2 UVLO Falling edge of VCC disables ADC 80 8 2.30 MIN TYP 500 20 100 10 2.80 90 2.0 90 2.25 120 12 2.95 V mV V mV A MAX UNITS
MAX6694
SMBus-COMPATIBLE TIMING (Figures 3 and 4) (Note 4)
Repeat START Condition Setup Time START Condition Hold Time
tSU:STA
tHD:STA
STOP Condition Setup Time
tSU:STO
Clock Low Period Clock High Period Data Hold Time
tLOW tHIGH tHD:DAT
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5-Channel Precision Temperature Monitor with Beta Compensation MAX6694
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.0V to +3.6V, VSTBY = VCC, TA = -40C to +125C, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25C.) (Note 1)
PARAMETER Data Setup Time Receive SMBCLK/SMBDATA Rise Time Receive SMBCLK/SMBDATA Fall Time Pulse Width of Spike Suppressed SMBus Timeout SYMBOL tSU:DAT tR tF tSP tTIMEOUT SMBDATA low period for interface reset 0 25 37 CONDITIONS fSMBCLK = 100kHz fSMBCLK = 400kHz fSMBCLK = 100kHz fSMBCLK = 400kHz MIN 250 100 1 0.3 300 50 45 TYP MAX UNITS ns s ns ns ms
Note 2: Note 3: Note 4: Note 5: Note 6:
All parameters are tested at TA = +85C. Specifications over temperature are guaranteed by design. Beta = 0.5 for channel 1 remote transistor. Timing specifications are guaranteed by design. The serial interface resets when SMBCLK is low for more than tTIMEOUT. A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SMBCLK's falling edge.
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5-Channel Precision Temperature Monitor with Beta Compensation
Typical Operating Characteristics
(VCC = 3.3V, VSTBY = VCC, TA = +25C, unless otherwise noted.)
SOFTWARE STANDBY SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX6694 toc01
MAX6694
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX6694 toc02
REMOTE-DIODE TEMPERATURE ERROR vs. REMOTE-DIODE TEMPERATURE
4 TEMPERATURE ERROR (C) 3 2 1 0 -1 -2 -3 -4 CHANNEL 1 CHANNEL 2
MAX6694 toc03
3.8 3.7 SUPPLY CURRENT (A) 3.6 3.5 3.4 3.3 3.2 3.1 3.0 3.0 3.1 3.2 3.3 3.4 3.5
650 600 SUPPLY CURRENT (A) 550 500 450 400 350 LOW BETA DIODE CONNECTED TO CHANNEL 1 WITH RESISTANCE CANCELLATION AND LOW BETA
5
-5 3.0 3.2 3.4 SUPPLY VOLTAGE (V) 3.6 0 25 50 75 100 125 TEMPERATURE (C)
3.6
SUPPLY VOLTAGE (V)
LOCAL TEMPERATURE ERROR vs. DIE TEMPERATURE
MAX6694 toc04
REMOTE-DIODE TEMPERATURE ERROR vs. POWER-SUPPLY NOISE FREQUENCY
MAX6694 toc05
LOCAL TEMPERATURE ERROR vs. POWER-SUPPLY NOISE FREQUENCY
4 TEMPERATURE ERROR (C) 3 2 1 0 -1 -2 -3 -4 100mVP-P
MAX6694 toc06 MAX6694 toc09
4 3 TEMPERATURE ERROR (C) 2 1 0 -1 -2 -3 0 25 50 75 100
5 4 TEMPERATURE ERROR (C) 3 2 1 0 -1 -2 -3 -4 CHANNEL 1 CHANNEL 2 100mVP-P
5
125
-5 0.001
0.010
0.100
1.000
10.000
-5 0.001
0.010
0.100
1.000
10.000
DIE TEMPERATURE (C)
FREQUENCY (MHz)
FREQUENCY (MHz)
CH 2 REMOTE-DIODE TEMPERATURE ERROR vs. COMMON-MODE NOISE FREQUENCY
3 TEMPERATURE ERROR (C) 2 1 0 -1 -2 -3 -4 -5 0.1 1.0 FREQUENCY (MHz) 10.0 100mVP-P
MAX6694 toc07
CH 1 REMOTE-DIODE TEMPERATURE ERROR vs. CAPACITANCE
4 TEMPERATURE ERROR (C) 3 2 1 0 -1 -2 -3 -4 -5 1 10 CAPACITANCE (nF) 100
MAX6694 toc08
CH 2 REMOTE-DIODE TEMPERATURE ERROR vs. CAPACITANCE
5 4 TEMPERATURE ERROR (C) 3 2 1 0 -1 -2 -3 -4 -5 1 10 CAPACITANCE (nF) 100
4
5
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5-Channel Precision Temperature Monitor with Beta Compensation MAX6694
Pin Description
PIN TSSOP TQFN-EP NAME FUNCTION Combined Current Source and A/D Positive Input for Channel 1 Remote Transistor. Connect to the emitter of a low beta transistor. Leave unconnected or connect to VCC if no remote transistor is used. Place a 100pF capacitor between DXP1 and DXN1 for noise filtering. Base Input for Channel 1 Remote Diode. Connect to the base of a PNP temperaturesensing transistor. Combined Current Source and A/D Positive Input for Channel 2 Remote Diode. Connect to the anode of a remote-diode-connected temperature-sensing transistor. Leave unconnected or connect to VCC if no remote diode is used. Place a 100pF capacitor between DXP2 and DXN2 for noise filtering. Cathode Input for Channel 2 Remote Diode. Connect the cathode of the channel 2 remote-diode-connected transistor to DXN2. Combined Current Source and A/D Positive Input for Channel 3 Remote Diode. Connect to the anode of a remote-diode-connected temperature-sensing transistor. Leave unconnected or connect to VCC if no remote diode is used. Place a 100pF capacitor between DXP3 and DXN3 for noise filtering. Cathode Input for Channel 3 Remote Diode. Connect the cathode of the channel 3 remote-diode-connected transistor to DXN3. Combined Current Source and A/D Positive Input for Channel 4 Remote Diode. Connect to the anode of a remote-diode-connected temperature-sensing transistor. Leave unconnected or connect to VCC if no remote diode is used. Place a 100pF capacitor between DXP4 and DXN4 for noise filtering. Cathode Input for Channel 4 Remote Diode. Connect the cathode of the channel 4 remote-diode-connected transistor to DXN4. Active-Low Standby Input. Drive STBY low to place the MAX6694 in standby mode, or high for operate mode. Temperature and threshold data are retained in standby mode. No Connection. Must be connected to ground. Overtemperature Active-Low, Open-Drain Output. OVERT asserts low when the temperature of channels 1, 4, 5, and 6 exceeds the programmed threshold limit. Supply Voltage Input. Bypass to GND with a 0.1F capacitor. SMBus Alert (Interrupt), Active-Low, Open-Drain Output. ALERT asserts low when the temperature of any channel exceeds the programmed ALERT threshold. SMBus Serial Data Input/Output. Connect to a pullup resistor. SMBus Serial Clock Input. Connect to a pullup resistor. Ground Exposed Pad. Connect to a large ground plane to maximize thermal performance. Not intended as an electrical connection point. (TQFN package only).
1
15
DXP1
2
16
DXN1
3
1
DXP2
4
2
DXN2
5
3
DXP3
6
4
DXN3
7
5
DXP4
8 9 10 11 12 13 14 15 16 --
6 7 8 9 10 11 12 13 14 --
DXN4 STBY N.C. OVERT VCC ALERT SMBDATA SMBCLK GND EP
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5-Channel Precision Temperature Monitor with Beta Compensation
Detailed Description
The MAX6694 is a precision multichannel temperature monitor that features one local and four remote temperature-sensing channels with a programmable alert threshold for each temperature channel and a programmable overtemperature threshold for channels 1 and 4 (see Figure 1). Communication with the MAX6694 is achieved through the SMBus serial interface and a dedicated alert output. The alarm outputs, OVERT and ALERT, assert if the software-programmed temperature thresholds are exceeded. ALERT typically serves as an interrupt, while OVERT can be connected to a fan, system shutdown, or other thermal-management circuitry.
ADC Conversion Sequence
In the default conversion mode, the MAX6694 starts the conversion sequence by measuring the temperature on channel 1, followed by 2, 3, local channel, and 4. The conversion result for each active channel is stored in the corresponding temperature data register.
MAX6694
Low-Power Standby Mode
Enter software standby mode by setting the STOP bit to 1 in the configuration 1 register. Enter hardware standby by pulling STBY low. Software standby mode disables the ADC and reduces the supply current to approximately 3A. Hardware standby mode halts the ADC clock, but the supply current is approximately
VCC
MAX6694
DXP ALARM ALU CURRENT SOURCES, BETA COMPENSATION AND MUX OVERT ALERT
DXN DXP2
DXN2 DXP3
INPUT BUFFER
ADC
REGISTER BANK COMMAND BYTE REMOTE TEMPERATURES
DXN3 DXP4 REF LOCAL TEMPERATURES ALERT THRESHOLD DXN4 OVERT THRESHOLD ALERT RESPONSE ADDRESS SMBus INTERFACE STBY
SMBCLK
SMBDATA
Figure 1. Internal Block Diagram
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5-Channel Precision Temperature Monitor with Beta Compensation
350A. During either software or hardware standby, data is retained in memory. During hardware standby, the SMBus interface is inactive. During software standby, the SMBus interface is active and listening for SMBus commands. The timeout is enabled if a start condition is recognized on SMBus. Activity on the SMBus causes the supply current to increase. If a standby command is received while a conversion is in progress, the conversion cycle is interrupted, and the temperature registers are not updated. The previous data is not changed and remains available.
MAX6694
SMBus Digital Interface
From a software perspective, the MAX6694 appears as a series of 8-bit registers that contain temperature measurement 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. The same SMBus slave address also provides access to all functions. The MAX6694 employs four standard SMBus protocols: write byte, read byte, send byte, and receive byte (Figure 2). The shorter receive byte protocol allows quicker transfers, provided that the correct data register was previously selected by a read byte instruction. Use caution with the shorter protocols in multimaster systems, since a second master could overwrite the command byte without informing the first master. Figure 3 is the SMBus write-timing diagram and Figure 4 is the SMBus read-timing diagram. The remote diode 1 measurement channel provides 11 bits of data (1 LSB = +0.125C). All other temperaturemeasurement channels provide 8 bits of temperature data (1 LSB = +1C). The 8 most significant bits (MSBs)
Operating-Current Calculation
The MAX6694 operates at different operating-current levels depending on how many external channels are in use. Assume that ICC1 is the operating current when the MAX6694 is converting the remote channel 1 and ICC2 is the operating current when the MAX6694 is converting the other channels. For the MAX6694 with remote channel 1 and n other remote channels connected, the operating current is: ICC = (2 x ICC1 + ICC2 + n x ICC2)/(n + 3)
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 TO WHICH REGISTER YOU ARE WRITING ACK DATA 8 BITS DATA BYTE: DATA GOES INTO THE REGISTER SET BY THE COMMAND BYTE (TO SET THRESHOLDS, CONFIGURATION MASKS, AND SAMPLING RATE) 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 ACK P 1
READ BYTE FORMAT
S ADDRESS 7 BITS SLAVE ADDRESS: EQUIVALENT TO CHIP SELECT LINE WR ACK COMMAND 8 BITS COMMAND BYTE: SELECTS FROM WHICH REGISTER YOU ARE READING ACK S
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
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
Figure 2. SMBus Protocols
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5-Channel Precision Temperature Monitor with Beta Compensation MAX6694
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 3. 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 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 CLOCKE D 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 4. SMBus Read-Timing Diagram
Table 1. Main Temperature Register (High Byte) Data Format
TEMP (C) > +127 +127 +126 +25 0 <0 Diode fault (short or open) DIGITAL OUTPUT 0111 1111 0111 1111 0111 1110 0001 1001 0000 0000 0000 0000 1111 1111
Table 2. Extended Resolution Temperature Register (Low Byte) Data Format
TEMP (C) 0 +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
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5-Channel Precision Temperature Monitor with Beta Compensation
can be read from the local temperature and remote temperature registers. The remaining 3 bits for remote diode 1 can be read from the extended temperature register. If extended resolution is desired, the extended resolution register should be read first. This prevents the most significant bits from being overwritten by new conversion results until they have been read. If the most significant bits have not been read within an SMBus timeout period (nominally 37ms), normal updating continues. Table 1 shows the main temperature register (high-byte) data format, and Table 2 shows the extended resolution register (low-byte) data format.
MAX6694
The ALERT output is open-drain so that multiple devices can share a common interrupt line. All ALERT interrupts can be masked using the configuration 3 register. The POR state of these registers is shown in Table 1.
ALERT Response Address
The SMBus alert response interrupt pointer provides quick fault identification for simple slave devices that lack the complex logic needed to be a bus master. Upon receiving an interrupt signal, the host master can broadcast a receive byte transmission to the alert response slave address (see the Slave Address section). Then, 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 I2C 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 acknowledgment 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 alert response protocol clears the output latch. If the condition that caused the alert still exists, the MAX6694 reasserts the ALERT interrupt at the end of the next conversion.
Diode Fault Detection
If a channel's input DXP_ and DXN_ are left open, the MAX6694 detects a diode fault. An open diode fault does not cause either ALERT or OVERT to assert. A bit in the status register for the corresponding channel is set to 1 and the temperature data for the channel is stored as all 1s (FFh). It takes approximately 4ms for the MAX6694 to detect a diode fault. Once a diode fault is detected, the MAX6694 goes to the next channel in the conversion sequence.
Alarm Threshold Registers
There are seven alarm threshold registers that store overtemperature ALERT and OVERT threshold values. Five of these registers are dedicated to storing one local alert temperature threshold limit and four remote alert temperature threshold limits (see the ALERT Interrupt Mode section). The remaining two registers are dedicated to remote channels 1 and 4 to store overtemperature threshold limits (see the OVERT Overtemperature Alarm section). Access to these registers is provided through the SMBus interface.
OVERT Overtemperature Alarms
The MAX6694 has two overtemperature registers that store remote alarm threshold data for the OVERT output. OVERT is asserted when a channel's measured temperature is greater than the value stored in the corresponding threshold register. OVERT remains asserted until the temperature drops below the programmed threshold minus 4C hysteresis. An overtemperature output can be used to activate a cooling fan, send a warning, initiate clock throttling, or trigger a system shutdown to prevent component damage. See Table 3 for the POR state of the overtemperature threshold registers.
ALERT Interrupt Mode
An ALERT interrupt occurs when the internal or external temperature reading exceeds a high-temperature limit (user programmable). The ALERT interrupt output signal can be cleared by reading the status register(s) associated with the fault(s) or by successfully responding to an alert response address transmission by the master. In both cases, the alert is cleared but is reasserted at the end of the next conversion if the fault condition still exists. The interrupt does not halt automatic conversions.
Command Byte Functions
The 8-bit command byte register (Table 3) is the master index that points to the various other registers within the MAX6694. This register's POR state is 0000 0000.
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5-Channel Precision Temperature Monitor with Beta Compensation MAX6694
Table 3. Command Byte Register Bit Assignment
REGISTER Local Remote 1 Remote 2 Remote 3 Remote 4 Configuration 1 Configuration 2 Configuration 3 Status1 Status2 Status3 Local ALERT High Limit Remote 1 ALERT High Limit Remote 2 ALERT High Limit Remote 3 ALERT High Limit Remote 4 ALERT High Limit Remote 1 OVERT High Limit Remote 4 OVERT High Limit Remote 1 Extended Temperature Manufacturer ID ADDRESS (HEX) 07 01 02 03 04 41 42 43 44 45 46 17 11 12 13 14 21 24 09 0A POR STATE (HEX) 00 00 00 00 00 0C 00 00 00 00 00 5A 6E 7F 64 64 6E 7F 00 4D READ/ WRITE R R R R R R/W R/W R/W R R R R/W R/W R/W R/W R/W R/W R/W R R DESCRIPTION Read local temperature register Read channel 1 remote temperature register Read channel 2 remote temperature register Read channel 3 remote temperature register Read channel 4 remote temperature register Read/write configuration register 1 Read/write configuration register 2 Read/write configuration register 3 Read status register 1 Read status register 2 Read status register 3 Read/write local alert high-temperature threshold limit register Read/write channel 1 remote-diode alert high-temperature threshold limit register Read/write channel 2 remote-diode alert high-temperature threshold limit register Read/write channel 3 remote-diode alert high-temperature threshold limit register Read/write channel 4 remote-diode alert high-temperature threshold limit register Read/write channel 1 remote-diode overtemperature threshold limit register Read/write channel 4 remote-diode overtemperature threshold limit register Read channel 1 remote-diode extended temperature register Read manufacturer ID
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5-Channel Precision Temperature Monitor with Beta Compensation MAX6694
Configuration Byte Functions
There are three read-write configuration registers (Tables 4, 5, and 6) that can be used to control the MAX6694's operation. tion exists, but the ALERT output reasserts at the end of the next conversion. The bits indicating the fault for the OVERT interrupt output clear only on reading the status 2 register even if the fault conditions still exist. Reading the status 2 register does not clear the OVERT interrupt output. To eliminate the fault condition, either the measured temperature must drop below the temperature threshold minus the hysteresis value (4C), or the trip temperature must be set at least 4C above the current temperature.
Configuration 1 Register The configuration 1 register (Table 4) has several functions. Bit 7 (MSB) is used to put the MAX6694 either in software standby mode (STOP) or continuous conversion mode. Bit 6 resets all registers to their POR conditions and then clears itself. Bit 5 disables the SMBus timeout. Bit 3 enables resistance cancellation on channel 1. See the Series Resistance Cancellation section for more details. Bit 2 enables beta compensation on channel 1. See the Beta Compensation section for more details. The remaining bits of the configuration 1 register are not used. The POR state of this register is 0000 0000 (00h). Configuration 2 Register The configuration 2 register functions are described in Table 5. Bits [6:0] are used to mask the ALERT interrupt output. Bit 6 masks the local alert interrupt and bits 5 through bit 2 mask the remote alert interrupts. The power-up state of this register is 0000 1100 (0Ch). Configuration 3 Register Table 6 describes the configuration 3 register. Bits 5, 4, 3, and 0 mask the OVERT interrupt output for channels 4 and 1. The remaining bits, 7, 6, 5, 4, 2, and 1, are reserved. The power-up state of this register is 0000 0000 (00h).
Applications Information
Remote-Diode Selection
The MAX6694 directly measures the die temperature of CPUs and other ICs that have on-chip temperaturesensing diodes (see the Typical Application Circuit) or it can measure the temperature of a discrete diodeconnected transistor.
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 MAX6694 is optimized for n = 1.006 (channel 1) and n = 1.008 (channels 2, 3, and 4). A thermal diode on the substrate of an IC is normally a pnp with the base and emitter brought out to the collector (diode connection) grounded. DXP_ must be connected to the anode (emitter) and DXN_ must be connected to the cathode (base) of this pnp. If a sense transistor with an ideality factor other than 1.006 or 1.008 is used, the output data is different from the data obtained with the optimum ideality factor. 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 and nNOMIMAL for channel 1 of the MAX6694 is 1.009. As an example, assume you want to use the MAX6694 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 1.009 TACTUAL = TM x NOMINAL = TM x = TM (1.00699) 1.002 n1
Status Register Functions
Status registers 1, 2, and 3 (Tables 7, 8, and 9) indicate which (if any) temperature thresholds have been exceeded and if there is an open-circuit or short-circuit fault detected with the external sense junctions. Status register 1 indicates if the measured temperature has exceeded the threshold limit set in the ALERT registers for the local or remote-sensing diodes. Status register 2 indicates if the measured temperature has exceeded the threshold limit set in the OVERT registers. Status register 3 indicates if there is a diode fault (open or short) in any of the remote-sensing channels. Bits in the alert status register clear by a successful read, but set again after the next conversion unless the fault is corrected, either by a drop in the measured temperature 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 deasserted by either reading status register 1 or by successfully responding to an alert response address. In both cases, the alert is cleared even if the fault condi12
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5-Channel Precision Temperature Monitor with Beta Compensation MAX6694
Table 4. Configuration 1 Register
BIT 7 (MSB) 6 5 4 3 2 1 0 NAME STOP POR TIMEOUT Reserved Resistance cancellation Beta compensation Reserved Reserved POR STATE 0 0 0 0 1 1 0 0 FUNCTION Standby Mode Control Bit. If STOP is set to logic 1, the MAX6694 stops converting and enters standby mode. Reset Bit. Set to logic 1 to put the device into its power-on state. This bit is selfclearing. Timeout Enable Bit. Set to logic 0 to enable SMBus timeout. Reserved. Must set to 0. Resistance Cancellation Bit. When set to logic 1, the MAX6694 cancels series resistance in the channel 1 thermal diode. Beta Compensation Bit. When set to logic 1, the MAX6694 compensates for low beta in the channel 1 thermal sensing transistor. -- --
Table 5. Configuration 2 Register
BIT 7 (MSB) 6 5 4 3 2 1 0 NAME Reserved Mask Local ALERT Reserved Reserved Mask ALERT 4 Mask ALERT 3 Mask ALERT 2 Mask ALERT 1 POR STATE 0 0 0 0 0 0 0 0 -- Local Alert Mask. Set to logic 1 to mask local channel ALERT. -- -- Channel 4 Alert Mask. Set to logic 1 to mask channel 4 ALERT. Channel 3 Alert Mask. Set to logic 1 to mask channel 3 ALERT. Channel 2 Alert Mask. Set to logic 1 to mask channel 2 ALERT. Channel 1 Alert Mask. Set to logic 1 to mask channel 1 ALERT. FUNCTION
Table 6. Configuration 3 Register
BIT 7 (MSB) 6 5 4 3 2 1 0 NAME Reserved Reserved Reserved Reserved Mask OVERT 4 Reserved Reserved Mask OVERT 1 POR STATE 0 0 0 0 0 0 0 0 -- -- -- -- Channel 4 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 4 OVERT. -- -- Channel 1 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 1 OVERT. FUNCTION
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13
5-Channel Precision Temperature Monitor with Beta Compensation MAX6694
Table 7. Status 1 Register
BIT 7 (MSB) 6 5 4 3 NAME Reserved Local ALERT Reserved Reserved Remote 4 ALERT POR STATE 0 0 0 0 0 -- Local Channel High-Alert Bit. This bit is set to logic 1 when the local temperature exceeds the temperature threshold limit in the local ALERT highlimit register. -- -- Channel 4 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 4 remote-diode temperature exceeds the temperature threshold limit in the remote 4 ALERT high-limit register. Channel 3 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 3 remote-diode temperature exceeds the programmed temperature threshold limit in the remote 3 ALERT high-limit register. Channel 2 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 2 remote-diode temperature exceeds the temperature threshold limit in the remote 2 ALERT high-limit register. Channel 1 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 1 remote-diode temperature exceeds the temperature threshold limit in the remote 1 ALERT high-limit register. FUNCTION
2
Remote 3 ALERT
0
1
Remote 2 ALERT
0
0
Remote 1 ALERT
0
Table 8. Status 2 Register
BIT 7 (MSB) 6 5 4 3 2 1 0 NAME Reserved Reserved Reserved Reserved Remote 4 OVERT Reserved Reserved Remote 1 OVERT POR STATE 0 0 0 0 0 0 0 0 -- -- -- -- Channel 4 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when the channel 4 remote-diode temperature exceeds the temperature threshold limit in the remote 4 OVERT high-limit register. -- -- Channel 1 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when the channel 1 remote-diode temperature exceeds the temperature threshold limit in the remote 1 OVERT high-limit register. FUNCTION
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5-Channel Precision Temperature Monitor with Beta Compensation MAX6694
Table 9. Status 3 Register
BIT 7 (MSB) 6 5 4 3 2 1 0 NAME Reserved Reserved Reserved Diode fault 4 Diode fault 3 Diode fault 2 Diode fault 1 Reserved POR STATE 0 0 0 0 0 0 0 0 -- Not Used. 0 at POR, then 1. Not Used. 0 at POR, then 1. Channel 4 Remote-Diode Fault Bit. This bit is set to 1 when DXP4 and DXN4 are open circuit or when DXP4 is connected to VCC. Channel 3 Remote-Diode Fault Bit. This bit is set to 1 when DXP3 and DXN3 are open circuit or when DXP3 is connected to VCC. Channel 2 Remote-Diode Fault Bit. This bit is set to 1 when DXP2 and DXN2 are open circuit or when DXP2 is connected to VCC. Channel 1 Remote-Diode Fault Bit. This bit is set to 1 when DXP1 and DXN1 are open circuit or when DXP1 is connected to VCC. -- FUNCTION
For a real temperature of +85C (358.15K), the measured temperature is +84.41C (357.56K), an error of -0.590C.
Series Resistance Cancellation
Some thermal diodes on high-power ICs can have excessive series resistance, which can cause temperature measurement errors with conventional remote temperature sensors. Channel 1 of the MAX6694 has a series resistance cancellation feature (enabled by bit 3 of the configuration 1 register) that eliminates the effect of diode series resistance. Set bit 3 to 1 if the series resistance is large enough to affect the accuracy of channel 1. The series resistance cancellation function increases the conversion time for channel 1 by 125ms. This feature cancels the bulk resistance of the sensor and any other resistance in series (wire, contact resistance, etc.). The cancellation range is from 0 to 100.
function that, when enabled, eliminates the effect of low beta values. This function is enabled at power-up and can be disabled using bit 2 of the configuration register. Whenever low beta compensation is enabled, series-resistance cancellation must be enabled. When a sense transistor's base and collector are shorted together (as with a discrete sensing "diode"), disable beta compensation.
Discrete Remote Diodes
When the remote-sensing diode is a discrete transistor, its collector and base must be connected together. Table 10 lists examples of discrete transistors that are appropriate for use with the MAX6694. The transistor must be a small-signal type with a relatively high forward voltage; otherwise, the A/D input voltage range
Beta Compensation
The MAX6694 is optimized for use with a substrate PNP remote-sensing transistor on the die of the target IC. DXP1 connects to the emitter of the sensing transistor and DXN1 connects to the base. The collector is grounded. Such transistors can have very low beta (less than 1) when built in processes with 65nm and smaller geometries. Because of the very low beta, standard "remote diode" temperature sensors may exhibit large errors when used with these transistors. Channel 1 of the MAX6694 incorporates a beta compensation
Table 10. Remote-Sensors Transistor Manufacturers (for Channels 2, 3, and 4)
MANUFACTURER Central Semiconductor (USA) Rohm Semiconductor (USA) Samsung (Korea) Siemens (Germany) Zetex (England) MODEL NO. CMPT3904 SST3904 KST3904-TF SMBT3904 FMMT3904CT-ND
Note: Discrete transistors must be diode connected (base shorted to collector).
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15
5-Channel Precision Temperature Monitor with Beta Compensation
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. Manufacturers of discrete transistors do not normally specify or guarantee ideality factor. This is normally not a problem since good-quality discrete transistors tend to have ideality factors that fall within a relatively narrow range. We have observed variations in remote temperature readings of less than 2C with a variety of discrete transistors. Still, it is good design practice to verify good consistency of temperature readings with several discrete transistors from any manufacturer under consideration. When measuring temperature with discrete remote transistors, the best thermal response times are obtained with transistors in small packages (i.e., SOT23 or SC70). 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.
MAX6694
ADC Noise Filtering
The integrating ADC has good noise rejection for lowfrequency signals, such as power-supply hum. In environments with significant high-frequency EMI, connect an external 100pF capacitor between DXP_ and DXN_. Larger capacitor values can be used for added filtering, but do not exceed 100pF because it can introduce errors due to the rise time of the switched current source. High-frequency noise reduction is needed for high-accuracy remote measurements. Noise can be reduced with careful PCB layout as discussed in the PCB Layout section.
Unused Diode Channels
If one or more of the remote diode channels is not needed, disconnect the DXP and DXN inputs for that channel, or connect the DXP input to VCC. The status register indicates a diode "fault" for this channel and the channel is ignored during the temperature-measurement sequence. It is also good practice to mask any unused channels immediately upon power-up by setting the appropriate bits in the Configuration 2 and Configuration 3 registers. This will prevent unused channels from causing ALERT or OVERT to assert.
Slave Address
The slave address for the MAX6694 is shown in Table 11.
Table 11. Slave Address
DEVICE ADDRESS A7 1 A6 0 A5 0 A4 1 A3 1 A2 0 A1 1 A0 R/W
Thermal Mass and Self-Heating
When sensing local temperature, the MAX6694 measures the temperature of the PCB to which it is soldered. The leads provide a good thermal path between the PCB traces and the die. As with all IC temperature sensors, thermal conductivity between the die and the ambient air is poor by comparison, making air temperature measurements impractical. Because the thermal mass of the PCB is far greater than that of the MAX6694, the device follows temperature changes on the PCB with little or no perceivable delay. When measuring the temperature of a CPU or other IC with an onchip sense junction, thermal mass has virtually no effect; the measured temperature of the junction tracks the actual temperature within a conversion cycle.
PCB Layout
Follow these guidelines to reduce the measurement error when measuring remote temperature: 1) Place the MAX6694 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 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.
16
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5-Channel Precision Temperature Monitor with Beta Compensation
3) Route the DXP and DXN traces in parallel and in close proximity to each other. Each parallel pair of traces should go to a remote diode. Route these traces away from any higher voltage traces, such as +12VDC. Leakage currents from PCB 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 5). 4) Route through as few vias and crossunders as possible to minimize copper/solder thermocouple effects. 5) Use wide traces when practical. 5mil to 10mil traces are typical. Be aware of the effect of trace resistance on temperature readings when using long, narrow traces. 6) When the power supply is noisy, add a resistor (up to 47) in series with VCC.
GND
Twisted-Pair and Shielded Cables
Use a twisted-pair cable to connect the remote sensor for remote-sensor distances 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 dis-
@@ ;;
MAX6694
5 mils TO 10 mils 5 mils TO 10 mils DXP MINIMUM 5 mils TO 10 mils DXN 5 mils TO 10 mils GND
Figure 5. Recommended DXP-DXN PCB Traces. The two outer guard traces are recommended if high-voltage traces are near the DXN and DXP traces.
tances 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 100pF 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.
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5-Channel Precision Temperature Monitor with Beta Compensation MAX6694
Pin Configurations
TOP VIEW +
DXP1 1 DXN1 2 DXP2 3 DXN2 4 DXP3 5 DXN3 6 DXP4 7 DXN4 8 16 GND 15 SMBCLK
MAX6694 MAX6694
SMBDATA ALERT
TOP VIEW
MAX6694
14 SMBDATA 13 ALERT 12 VCC 11 OVERT 10 N.C. 9 STBY SMBCLK GND DXP1 DXN1 13 14 15 16
12 11 10 9
VCC OVERT
MAX6694
8 7 6 5
N.C. STBY DXN4 DXP4
+
1
2
3
TSSOP
TQFN-EP*
*EXPOSED PAD. CONNECT EP TO GND.
Chip Information
PROCESS: BiCMOS
PACKAGE TYPE 16 TSSOP 16 TQFN-EP
For the latest package outline information, go to www.maxim-ic.com/packages. PACKAGE CODE U16-1 T1655-2 DOCUMENT NO. 21-0066 21-0140
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.
18 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
DXP2 DXN2 DXP3 DXN3
Package Information
4

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