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19-2117; Rev 1; 5/06
Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors
General Description
The MAX6655/MAX6656 are precise voltage and temperature monitors. The digital thermometer reports the temperature of two remote sensors and its own die temperature. The remote sensors are diode-connected transistors--typically a low-cost, easily mounted 2N3906 PNP type--that replace conventional thermistors or thermocouples. Remote accuracy is 1C for multiple transistor manufacturers with no calibration necessary. The remote channels can also measure the die temperature of other ICs, such as microprocessors, that contain a substrate-connected PNP with its collector grounded and its base and emitter available for temperature-sensing purposes. The temperature is digitized with 11-bit resolution. The MAX6655/MAX6656 also measure their own supply voltage and three external voltages with 8-bit resolution. Each voltage input's sensitivity is set to give approximately 3/4-scale output code when the input voltage is at its nominal value. The MAX6655 operates at +5V supply and its second voltage monitor is 3.3V. The MAX6656 operates on a +3.3V supply and its second voltage monitor is 5V. The 2-wire serial interface accepts standard SMBusTM Write Byte, Read Byte, Send Byte, and Receive Byte commands to program the alarm thresholds and to read data. The MAX6655/MAX6656 also provide SMBus alert response and timeout functions. The MAX6655/MAX6656 measure automatically and autonomously, with the conversion rate programmable. The adjustable rate allows the user to control the supply current. In addition to the SMBus ALERT output, the MAX6655/ MAX6656 feature an OVERT output, which is used as a temperature reset that remains active only while the temperature is above the maximum temperature limit. The OVERT output is optimal for fan control or for system shutdown. Three Temperature Channels Two Remote PN Junctions One Local Sensor Four Voltage Channels +12V, +5V, +3.3V, +2.5V Three External Monitors One Internal Supply Monitor 11-Bit, 0.125C Resolution High Accuracy: 1C Over +60C to +100C Temperature Range Programmable Under/Over-Threshold Alarms Programmable Power-Saving Mode No Calibration Required SMBus/I2C-Compatible Interface OVERT Output for Fan Control and System Shutdown
Features
MAX6655/MAX6656
Ordering Information
PART MAX6655MEE MAX6656MEE TEMP RANGE -55C to +125C -55C to +125C PINPACKAGE 16 QSOP 16 QSOP PKG CODE E16-5 E16-5
Typical Application Circuit appears at end of data sheet.
Pin Configuration
TOP VIEW
VCC 1 16 STBY 15 SMBCLK 14 OVERT DXP1 2 DXN1 3 ADD0 4 ADD1 5 DXP2 6 DXN2 7 GND 8
Applications
Notebooks Thin Clients Servers Workstations Communication Equipment Desktop PC
S. *P, Is ae cSMBus is a trademark of Intel Corp.
MAX6655 MAX6656
13 SMBDATA 12 ALERT 11 VIN2 10 VIN1 9 VIN3
QSOP
________________________________________________________________ Maxim Integrated Products
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Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors MAX6655/MAX6656
ABSOLUTE MAXIMUM RATINGS
VCC to GND ..............................................................-0.3V to +6V DXN_ to GND ........................................................-0.3V to +0.8V SMBCLK, SMBDATA, ALERT, STBY, OVERT to GND .....................................................-0.3V to +6V VIN1 to GND............................................................-0.3V to +16V VIN2 to GND..............................................................-0.3V to +6V VIN3 to GND..............................................................-0.3V to +6V All Other Pins to GND.................................-0.3V to (VCC + 0.3V) SMBDATA, ALERT, OVERT Current....................-1mA to +50mA DXN_ Current......................................................................1mA ESD Protection (all pins, Human Body Model) ..................2000V Continuous Power Dissipation (TA = +70C) 16-Pin QSOP (derate 8.30mW/C above +70C)........667mW Operating Temperature Range .........................-55C to +125C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 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 +3.6V for MAX6656, VCC = +4.5V to +5.5V for MAX6655, TA = -55C to +125C, unless otherwise noted. Typical values are at VCC = +3.3V for MAX6656, VCC = +5.0V for MAX6655, TA = +25C.)
PARAMETER Supply Range Accuracy (Local Sensor) Accuracy (Remote Sensor) Temperature Measurement Resolution ADC Input Impedance ADC Total Error VIN ADC Resolution Undervoltage Lockout Threshold Undervoltage Lockout Hysteresis Power-On Reset (POR) Threshold POR Threshold Hysteresis Standby Current DXP and DXN Leakage Current Average Operating Current Conversion Time for Single Temperature Measurement Monitoring Cycle Time tCON tMONI SMBus static, STBY = GND In standby mode Continuous temperature mode From stop bit to conversion completed Total of 3 temperature plus 4 voltage measurements 95 550 125 625 VCC, falling edge 1 UVLO VCC input, disables A/D conversion, falling edge 2.50 ZIN VIN1, VIN2, VIN3 input resistance VIN1, VIN2, VIN3 between 30% and 120% of nominal 100 1 8 2.70 90 1.7 90 3 10 2 1000 155 2.5 2.90 1.5 SYMBOL VCC +60C TA +100C 0C TA +125C +60C TRJ +100C 0C TRJ +120C 0.125 11 CONDITIONS MIN 3.0 TYP MAX 5.5 1.5 3 1 3 UNITS V C C C Bits k % Bits V mV V mV A A A ms ms
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Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.0V to +3.6V for MAX6656, VCC = +4.5V to +5.5V for MAX6655, TA = -55C to +125C, unless otherwise noted. Typical values are at VCC = +3.3V for MAX6656, VCC = +5.0V for MAX6655, TA = +25C.)
PARAMETER Remote Junction Current (DXP, DXN) Logic Input Low Voltage Logic Input High Voltage Input Leakage Current Output Low Sink Current Input Capacitance SMBus Timeout ALERT, OVERT Output Low Sink Current Output High Leakage Current SMBus TIMING 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 Data Hold Time Receive SMBCLK/SMBDATA Rise Time Receive SMBCLK/SMBDATA Fall Time Pulse Width of Spike Suppressed tSU:STA tHD:STA tSU:STO tLOW tHIGH tSU:DAT tHD:DAT tR tF tSP 0 90% to 90% 10% of SMBDATA to 90% of SMBCLK 90% of SMBCLK to 10% of SMBDATA 10% to 10% 90% to 90% 90% of SMBDATA to 10% of SMBCLK (Note 1) 4 250 0 1 300 50 fSCL tBUF 4.7 4.7 50 4 4 4.7 400 kHz s s ns s s s s ns s s ns ns VOL = +0.6V VOH = +5.5V 6 1 mA A VIL VIH ILEAK IOL CIN SMBCLK or SMBDATA time low for reset 30 SYMBOL High level Low level VCC = +3.0V to +5.5V VCC = +3.0V VCC = +5.5V VIN = GND or VCC VOL = +0.6V 5 35 60 2.1 2.6 1 6 CONDITIONS MIN 80 8 TYP 100 10 MAX 140 14 0.8 UNITS A
MAX6655/MAX6656
SMBus INTERFACE (SMBCLK, SMBDATA, STBY) V V A mA pF ms
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Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors MAX6655/MAX6656
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
TEMPERATURE ERROR vs. POWER-SUPPLY NOISE FREQUENCY
MAX6655/MAX6656 toc02
REMOTE TEMPERATURE ERROR vs. PC BOARD RESISTANCE
MAX6655/MAX6656 toc01
REMOTE TEMPERATURE ERROR vs. REMOTE-DIODE TEMPERATURE
5 REMOTE TEMPERATURE ERROR (C) 4 3 2 1 0 -1 -2 -3 -4 RANDOM SAMPLE 2N3906 20
20 REMOTE TEMPERATURE ERROR (C)
TEMPERATURE ERROR (C)
10 PATH = DXP TO GND 0 PATH = DXP TO VCC (5V) -10
15
VIN = SQUARE WAVE APPLIED TO VCC WITH NO VCC BYPASS CAPACITOR VIN = 250mVp-p REMOTE DIODE
10
5
-20 1 10 LEAKAGE RESISTANCE (M) 100
-5 -55 -5 45 95 TEMPERATURE (C)
0 0 10 20 30 40 50 FREQUENCY (MHz)
REMOTE TEMPERATURE ERROR vs. COMMON-MODE NOISE FREQUENCY
14 REMOTE TEMPERATURE ERROR (C) 12 10 8 VIN = 200mVp-p 6 4 VIN = 100mVp-p 2 0 0 10 20 30 40 50 FREQUENCY (MHz)
MAX6655/MAX6656 toc04
REMOTE TEMPERATURE ERROR vs. DXP-DXN CAPACITANCE
MAX6655/MAX6656 toc05
STANDBY SUPPLY CURRENT vs. CLOCK FREQUENCY
45 40 SUPPLY CURRENT (A) 35 30 25 20 15 10 SMBCLK IS DRIVEN RAIL-TO-RAIL
MAX6655/MAX6656 toc06
50
REMOTE TEMPERATURE ERROR (C)
VIN = SQUARE WAVE AC-COUPLED TO DXN
14 VCC = +5V 12 10 8 6 4 2 0 0 50 100 150 200 DXP-DXN CAPACITANCE (nF)
5 0 1 10 100 1000 SMBCLK FREQUENCY (kHz)
STANDBY SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX6655/MAX6656 toc07
RESPONSE TO THERMAL SHOCK
120 100 TEMPERATURE (C) 80 60 40 20 0
MAX6655/MAX6656 toc08
VOLTAGE ACCURACY vs. TEMPERATURE
12 10 8 6 4 2 0 VCC VIN2 VIN3 INPUT VOLTAGES ARE NOMINAL VIN1
MAX6655/MAX6656 toc09
140 120 SUPPLY CURRENT (A) 100 80 60 40 ADD0, ADD1 = HIGH-Z 20 0 0 1 2 3 4 5 SUPPLY VOLTAGE (V) ADD0, ADD1 = GND
REMOTE DIODE IMMERSED IN +115C FLUORINERT BATH
OUTPUT VOLTAGE (V)
-1
0
1
2 TIME (s)
3
4
5
0
20
40
60
80
100
120
TEMPERATURE (C)
4
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MAX6655/MAX6656 toc03
Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors
Pin Description
PIN 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 NAME VCC DXP1 DXN1 ADD0 ADD1 DXP2 DXN2 GND VIN3 VIN1 VIN2 ALERT SMBDATA OVERT SMBCLK STBY FUNCTION Supply Voltage. +5V for MAX6655; +3.3V for MAX6656. Bypass VCC to GND with a 0.1F capacitor. External Diode 1 Positive Connection. DXP1 is the combined current source and ADC positive input for remote-diode 1. If a remote-sensing junction is not used, connect DXP1 to DXN1. External Diode 1 Negative Connection. DXN1 is the combined current sink and ADC negative input for remote-diode 1. DXN1 is normally biased to a diode voltage above ground. SMBus Slave Address Select Input. ADD0 and ADD1 are sampled upon power-up. Table 5 is the truth table. SMBus Slave Address Select Input. ADD0 and ADD1 are sampled upon power-up. External Diode 2 Positive Connection. DXP2 is the combined current source and ADC positive input for remote-diode 2. If a remote-sensing junction is not used, connect DXP2 to DXN2. External Diode 2 Negative Connection. DXN2 is the combined current sink and ADC negative input for remote-diode 2. DXN2 is normally biased to a diode voltage above ground. Ground External Voltage Monitor 3. VIN3 is typically used to monitor +2.5V supplies. External Voltage Monitor 1. VIN1 is typically used to monitor +12V supplies. External Voltage Monitor 2. VIN2 is typically used to monitor voltage supplies of +3.3V for MAX6655 and +5.0V for MAX6656. SMBus Alert (Interrupt) Output, Open-Drain SMBus Serial-Data Input/Output, Open-Drain Overtemperature Alarm Output, Open-Drain. OVERT is an unlatched alarm output that responds to the programmed maximum temperature limit for all temperature channels. SMBus Serial-Clock Input Hardware Standby Input. Drive STBY low for low-power standby mode. Drive STBY high for normal operating mode. Temperature and comparison threshold data are retained in standby mode.
MAX6655/MAX6656
Detailed Description
The MAX6655/MAX6656 are voltage and temperature monitors that communicate through an SMBus-compatible interface with a microprocessor or microcontroller in thermal management applications. Essentially an 11-bit serial ADC with a sophisticated front end, the MAX6655/MAX6656 contain a switched-current source, a multiplexer, an ADC, an SMBus interface, and the associated control logic. Temperature data from the ADC is loaded into a data register, where it is automatically compared with data previously stored in over/undertemperature alarm threshold registers. Temperature data can be read at any time with 11 bits of resolution. The MAX6655/MAX6656 can monitor external supply voltages of typically 12V, 2.5V, and 3.3V for the MAX6655 and 5.0V for the MAX6656, as well as their own supply voltage. All voltage inputs are converted to an 8-bit code using an ADC. Each input voltage is scaled down by an
on-chip resistive-divider so that its output, at the nominal input voltage, is approximately 3/4 of the ADC's full-scale range, or a decimal count of 198.
ADC
The averaging ADC integrates over a 40ms period (typ) with excellent noise rejection. The ADC converts a temperature measurement in 125ms (typ) and a voltage measurement in 62.5ms (typ). For temperature measurements, the multiplexer automatically steers bias currents through the remote diode, then the forward voltage is measured and the temperature is computed. The DXN input is biased at one diode drop above ground by an internal diode to set up 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 about +1/2C error/. A 200V offset voltage at DXP-DXN causes about -1C error.
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Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors MAX6655/MAX6656
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 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 ACK COMMAND 8 bits Data Byte: writes data to the register commanded by the last read byte or write byte transmission S = Start condition P = Stop condition Shaded = Slave transmission A = Not acknowledged ACK P 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 A P RD ACK DATA 8 bits Data Byte: reads from the register set by the command byte A P WR ACK COMMAND 8 bits Command Byte: selects which register you are writing to ACK DATA 8 bits Data Byte: data goes into the register set by the co mma nd byte ( to se t thresholds, configuration masks, and sampling rate) ACK P
Send Byte Format S ADDRESS 7 bits WR
Figure 1. SMBus/I2C Protocols
ADC Conversion Sequence
Each time a conversion begins, all channels are converted, and the results of the measurements are available after the end of conversion. A BUSY status bit in the Status Byte shows that the device is actually performing a new conversion; however, even if the ADC is busy, the results of the previous conversion are always available. The conversion sequence for the MAX6655 (MAX6656) is External Diode 1, External Diode 2, Internal Diode, VIN3, VIN2 (VCC), VIN1, VCC (VIN2). The ADC always converts at maximum speed, but the time between a sequence of conversions is adjustable. The Conversion Rate Control Byte (Table 1) shows the possible delays between conversions. Disabling voltage or temperature measurements with the Configuration Byte makes the ADC complete the conversion sequence faster.
Low-Power Standby Mode
Standby mode disables the ADC and reduces the supply current drain to 3A (typ). Enter standby mode by forcing STBY low or through the RUN/STOP bit in the
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Configuration Byte register. Hardware and software standby modes behave identically; all data is retained in memory, and the SMBus interface is alive and listening for reads and writes. Standby mode is not a shutdown mode. Activity on the SMBus draws extra supply current (see Typical Operating Characteristics). Enter hardware standby mode by forcing STBY low. In a notebook computer, this line may be connected to the system SUSTAT# suspend-state signal. The STBY low state overrides any software conversion command. If a hardware or software standby command is received while a conversion is in progress, the conversion cycle is truncated, and the data from that conversion is not latched into the Temperature Reading register. The previous data is not changed and remains available. Supply current during the 125ms conversion is typically 550A. Between conversions, the instantaneous supply current is about 25A, due to the current consumed by the conversion-rate timer. With very low supply voltages (under the POR threshold), the supply current is higher due to the address input bias currents.
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Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors MAX6655/MAX6656
A tLOW B tHIGH C D E F G H I J K L M
SMBCLK
SMBDATA
tSU:STA
tHD:STA
tSU:DAT
tHD:DAT
tSU:STO tBUF
A = START CONDITION B = MSB OF ADDRESS CLOCKED INTO SLAVE C = LSB OF ADDRESS CLOCKED INTO SLAVE D = R/W BIT CLOCKED INTO SLAVE E = SLAVE PULLS SMBDATA LINE LOW
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO SLAVE H = LSB OF DATA CLOCKED INTO SLAVE I = MASTER PULLS DATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO SLAVE K = ACKNOWLEDGE CLOCK PULSE L = STOP CONDITION M = NEW START CONDITION
Figure 2. SMBus/I2C Write Timing Diagram
A
tLOW
B
tHIGH
C
D
E
F
G
H
I
J
K
L
M
SMBCLK
SMBDATA
tSU:STA
tHD:STA
tSU:DAT
tHD:DAT
tSU:STO tBUF
A = START CONDITION B = MSB OF ADDRESS CLOCKED INTO SLAVE C = LSB OF ADDRESS CLOCKED INTO SLAVE D = R/W BIT CLOCKED INTO SLAVE E = SLAVE PULLS SMBDATA LINE LOW
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO MASTER H = LSB OF DATA CLOCKED INTO MASTER I = MASTER PULLS DATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO SLAVE K = ACKNOWLEDGE CLOCK PULSE L = STOP CONDITION M = NEW START CONDITION
Figure 3. SMBus/I2C Read Timing Diagram
SMBus Digital Interface
From a software perspective, the MAX6655/MAX6656 appear as a set of byte-wide registers that contain temperature data, voltage data, alarm threshold values, and control bits. Use a standard SMBus 2-wire serial interface to read temperature data and write control bits and alarm threshold data.
The MAX6655/MAX6656 employ four standard SMBus protocols: Write Byte, Read Byte, Send Byte, and Receive Byte (Figures 1, 2, and 3). The two shorter protocols (Receive and Send) allow quicker transfers, provided that the correct data register was previously selected by a Write or 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.
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Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors MAX6655/MAX6656
+3V TO +5.5V
the T HIGH or T LOW alarms at their POR settings. Similarly, if DXP_ is short circuited to V CC, the ADC reads -1C for both remote channels, and the ALERT outputs are activated.
VCC MAX6655 MAX6656 SMBCLK SMBDATA ALERT OVERT DXP2 ADD0 ADD1 DXN2 GND TO SYSTEM SHUTDOWN
Alert Interrupts
Normally, the ALERT interrupt output signal is latched and can be cleared either by responding to the Alert Response Address or by reading the Status register. Interrupts are generated in response to T HIGH and TLOW, VHIGH and VLOW comparisons, and when the remote diode is faulted. The interrupt does not halt automatic conversions; new temperature data continues to be available over the SMBus interface after ALERT is asserted. The interrupt output pin is open-drain so multiple devices can share a common interrupt line. The interface responds to the SMBus Alert Response address, an interrupt pointer return-address feature (see the Alert Response Address section). Before taking corrective action, always check to ensure that an interrupt is valid by reading the current temperature. The alert activates only once per crossing of a given temperature threshold to prevent any reentrant interrupts. To enable a new interrupt, rewrite the value of the violated temperature threshold.
SMBus SERIAL INTERFACE (TO HOST)
2N3906
2200pF
Figure 4. System Shutdown Application
The temperature data is stored in internal registers RRTE, RRT2, and RLTS as 7 bits + sign in two's complement form with each LSB representing 1C. Additionally, the 3MSBs of the Extended Temperature register contain fractional temperature data with +0.125C resolution (Tables 2 and 3). The voltage data is stored in RV0, RV1, RV2, and RV3 as 8 bits in binary form (Table 4).
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 (0001100). Any slave device that generated an interrupt then attempts to identify itself by putting its own address on the bus (Table 5). 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 serviced (implies that the host interrupt input is level sensitive). The alert is cleared after the slave address is returned to the host.
OVERT Output
OVERT output is an unlatched open-drain output that behaves as a thermostat for fan control or system shutdown (Figure 4). This output responds to the current temperature. If the current temperature is above THIGH, OVERT activates and does not go inactive until the temperature drops below THIGH.
Diode Fault Alarm
A continuity fault detector at DXP detects whether the remote diode has an open-circuit condition, short-circuit to GND, or short-circuit DXP-to-DXN condition. At the beginning of each conversion, the diode fault is checked, and the Status Byte is updated. This fault detector is a simple voltage detector; if DXP rises above VCC - 1V (typ) or below VDXN + 50mV (typ), a fault is detected. Note that the diode fault isn't checked until a conversion is initiated, so immediately after POR, the status byte indicates no fault is present, even if the diode path is broken. If the remote channel is shorted (DXP to DXN or DXP to GND), the ADC reads 1111 1111 so as not to trip either
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Command Byte Functions
The 8-bit Command Byte register (Table 6) is the master index that points to the other registers within the MAX6655/MAX6656. 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 internal temperature data.
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Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors
Alarm Threshold Registers
Seventeen registers store ALARM and OVERT threshold data. The MAX6655/MAX6656 contain three registers for high-temperature (T HIGH ), three for lowtemperature (TLOW), four for high-voltage (VHIGH), four for low-voltage (VLOW) thresholds, and three more registers store OVERT data. If a measured temperature or voltage exceeds the corresponding alarm threshold value, an ALARM interrupt is asserted. OVERT asserts when temperature exceeds the corresponding alarm threshold value. The POR state of the THIGH register is full scale (0111 1111 or +127C). The POR state of the TLOW register is 1100 1001 or -55C. ed temperature. The base resistance has to be less than 100. Tight specification of forward-current gain (+50 to +150, for example) indicates that the manufacturer has good process controls and that the devices have consistent VBE characteristics. Do not use power transistors.
MAX6655/MAX6656
Self-Heating
Thermal mass can significantly affect the time required for a temperature sensor to respond to a sudden change in temperature. The thermal time constant of the 16-pin QSOP package is about 140s in still air. When measuring local temperature, it senses the temperature of the PC board to which it is soldered. The leads provide a good thermal path between the PC board traces and the MAX6655/MAX6656 die. Thermal conductivity between the MAX6655/MAX6656 die and the ambient air is poor by comparison. Because the thermal mass of the PC board is far greater than that of the MAX6655/MAX6656, the device follows temperature changes on the PC board with little or no perceivable delay. When measuring temperature with discrete remote sensors, the use of smaller packages, such as a SOT23, yields the best thermal response time. 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. 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. 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, at the minimum delay between conversions, and with ALERT sinking 1mA, the typical power dissipation is VCC x 550A + 0.4V x 1mA. Package JA is about 150C/W, so with VCC = +5V and no copper PC board heat sinking, the resulting temperature rise is: T = 3.1mW x 150C/W = +0.46C Even with these contrived circumstances, it is difficult to introduce significant self-heating errors.
Configuration Byte Functions
Configuration Bytes 1 and 2 (Tables 7 and 8) are used to mask (disable) interrupts, disable temperature and voltage measurements, and put the device in software standby mode. The serial interface can read back the contents of these registers.
Status Byte Functions
The two Status Byte registers (Tables 9 and 10) indicate which (if any) temperature or voltage thresholds have been exceeded. Status Byte 1 also indicates whether the ADC is converting and whether there is a fault in the remote-diode DXP-DXN path. After POR, the normal state of all the flag bits is zero, except the MSB, assuming none of the alarm conditions are present. The MSB toggles between 1 and 0 indicating whether the ADC is converting or not. A Status Byte is cleared by any successful read of that Status Byte. Note that the ALERT interrupt latch clears when the status flag bit is read, but immediately asserts after the next conversion if the fault condition persists. High and low alarm conditions can exist at the same time in the Status Byte because the MAX6655/MAX6656 are correctly reporting environmental changes.
Applications Information
Remote-Diode Selection
Remote temperature accuracy depends on having a good-quality, diode-connected transistor. See Table 11 for appropriate discrete transistors. The MAX6655/ MAX6656 can directly measure the die temperature of CPUs and other ICs with on-board temperature-sensing transistors. The transistor must be a small-signal type with a relatively high forward voltage. This ensures that the input voltage is within the ADC input voltage range. The forward voltage must be greater than 0.25V at 10A at the highest expected temperature. The forward voltage must be less than 0.95V at 100A at the lowest expect-
ADC Noise Filtering
The integrating ADC has inherently good noise rejection, especially of low-frequency signals such as 60Hz/120Hz power-supply hum. Micropower operation
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Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors MAX6655/MAX6656
places constraints on high-frequency noise rejection. Lay out the PC board carefully with proper external noise filtering for high-accuracy remote measurements in electrically noisy environments. Filter high-frequency electromagnetic interference (EMI) at DXP and DXN with an external 2200pF capacitor connected between the two inputs. This capacitor can be increased to about 3300pF (max), including cable capacitance. A capacitance higher than 3300pF introduces errors due to the rise time of the switched-current source. If necessary, bypass VIN_ pins with any appropriatevalue capacitor for greater noise performance. Do not put resistance in series with the inputs. Series resistance degrades voltage measurements.
GND 10MILS 10MILS DXP MINIMUM 10MILS DXN 10MILS GND
PC Board Layout
1) Place the MAX6655/MAX6656 as close as practical to the remote diode. In a noisy environment, such as a computer motherboard, this distance can be 4in to 8in (typ) or more, as long as the worst noise sources (such as CRTs, clock generators, memory buses, and ISA/PCI buses) are avoided. 2) Do not route the DXP-DXN lines next to the deflection coils of a CRT. Also, do not route the traces across a fast memory bus, which can easily introduce +30C error, even with good filtering. Otherwise, most noise sources are fairly benign. 3) Route the DXP and DXN traces parallel and close to each other, away from any high-voltage traces such as +12VDC. Avoid leakage currents from PC board contamination. A 20m leakage path from DXP to ground causes approximately +1C error. 4) Connect guard traces to GND on either side of the DXP-DXN traces when possible (Figure 5). With guard traces in place, routing near high-voltage traces is no longer an issue. 5) Route as few vias and crossunders as possible to minimize copper/solder thermocouple effects. 6) When introducing a thermocouple, make sure that both the DXP and the DXN paths have matching thermocouples. In general, PC board-induced thermocouples are not a serious problem. A copper-solder thermocouple exhibits 3V/C, and it takes approximately 200V of voltage error at DXP-DXN to cause a 1C measurement error, so most parasitic thermocouple errors are swamped out. 7) Use wide traces. Narrow traces are more inductive and tend to pick up radiated noise. The 10-mil widths and spacings recommended in Figure 5 are not absolutely necessary (as they offer only a minor
Figure 5. Recommended DXP/DXN PC Traces
improvement in leakage and noise), but use them where practical. 8) Note that copper cannot be used as an EMI shield. Placing a copper ground plane between the DXPDXN traces and traces carrying high-frequency noise signals does not help reduce EMI.
Twisted Pair and Shielded Cables
For remote-sensor distances longer than 8in, or in particularly noisy environments, a twisted pair is recommended. Its practical length is 6ft to 12ft (typ) before noise becomes a problem, as tested in a noisy electronics laboratory. For longer distances, the best solution is a shielded twisted pair like that used for audio microphones. For example, Belden #8451 works well for distances up to 100ft in a noisy environment. Connect the twisted pair to DXP and DXN and the shield to GND, and leave the shield's remote end unterminated. Excess capacitance at DX_ limits practical remote-sensor distances (see Typical Operating Characteristics). For very long cable runs, the cable's parasitic capacitance often provides noise filtering, so the recommended 2200pF capacitor can often be removed or reduced in value. Cable resistance also affects remote-sensor accuracy. A 1 series resistance introduces about +1/2C error.
Chip Information
TRANSISTOR COUNT: 26,783 PROCESS: BiCMOS
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Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors MAX6655/MAX6656
Table 1. Conversion Rate Control Byte
DATA (RCRA, 04H) 00h 01h 02h 03h 04h 05h 06h 07h WAIT TIME BETWEEN CONVERSION SEQUENCES (s) 0 0.125 0.250 0.500 1.000 2.000 4.000 4.000
Table 3. Extended Resolution Register
FRACTIONAL TEMPERATURE (C) 0 0.125 0.250 0.375 0.500 0.625 0.750 0.875 DIGITAL OUTPUT 0000 0000 0010 0000 0100 0000 0110 0000 1000 0000 1010 0000 1100 0000 1110 0000
Table 2. Temperature Data Format
TEMP (C) 130.00 127.00 126.00 25.25 0.50 0 -0.625 -65 Diode Fault (Short or Open) ROUNDED TEMP (C) +127 +127 +126 +25 +1 0 -1 -65 -- DIGITAL OUTPUT 0 111 1111 0 111 1111 0 111 1111 0 001 1001 0 000 0001 0 000 0000 1 111 1111 1 011 1111 1111 1111
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Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors MAX6655/MAX6656
Table 4. Voltage Data Format
ADC OUTPUT CODE LSB weight 64 ( 1/4 scale) 65 66 -- 128 ( 1/2 scale) -- 198 ( 3/4 scale) -- 210 211 -- 237 ( 5/4 scale) INPUT VOLTAGE AT VIN1 (+12V) 57.1mV 4.343V to 4.400V 4.400V to 4.457V 4.457V to 4.514V -- 8.000V to 8.057V -- 12.000V to 12.057V -- 12.686V to 12.743V 12.743V to 12.800V -- 14.228V to 14.285V INPUT VOLTAGE AT VIN2 (+5V) OR VCC 23.8mV 1.810V to 1.833V 1.833V to 1.857V 1.857V to 1.881V -- 3.333V to 3.357V -- 5.000V to 5.024V -- 5.286V to 5.310V 5.310V to 5.333V -- 5.929V to 5.952V INPUT VOLTAGE AT VIN2 (+3.3V) OR VCC 15.7mV 1.194V to 1.210V 1.210V to 1.226V 1.226V to 1.242V -- 2.200V to 2.216V -- 3.300V to 3.3157V -- 3.486V to 3.504V 3.504V to 3.521V -- 3.913V to 3.929V INPUT VOLTAGE AT VIN3 (+2.5V) 11.9mV 0.905V to 0.917V 0.917V to 0.929V 0.929V to 0.941V -- 1.250V to 1.262V -- 2.500V to 2.512V -- 2.643V to 2.655V 2.655V to 2.667V -- 2.964V to 2.976V
Table 5. Address Map (ADD[1:0])
ADD0 0 0 0 High-Z High-Z High-Z 1 1 1 ADD1 0 High-Z 1 0 High-Z 1 0 High-Z 1 ADDRESS 0011 0000 0011 0010 0011 0100 0101 0010 0101 0100 0101 0110 1001 1000 1001 1010 1001 1100
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Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors
Table 6. Command Byte Register Map
REGISTER RLTS RRTE RSL RCL RCRA RLHN RLLI RRHI RRLS WCA WCRW WLHO WLLM WRHA WRLN RRET1 RRET2 RLET RRT2 RRHL2 RRLL2 RLOL RLOL1 RLOL2 WLOL WROL1 WROL2 WRH2 WRL2 WV0HL WV0LL WV1HL WV1LL WV2HL WV2LL WV3HL WV3LL RV0HL RV0LL ADDRESS 00h 01h 02h 03h 04h 05h 06h 07h 08h 09h 0Ah 0Bh 0Ch 0Dh 0Eh 10h 11h 12h 13h 14h 15h 16h 17h 18h 19h 1Ah 1Bh 1Ch 1Dh 1Eh 1Fh 20h 21h 22h 23h 24h 25h 26h 27h POR STATE 0000 0000 0000 0000 0000 0000 0000 0000 0000 0010 0111 1111 1100 1001 0111 1111 1100 1001 N/A N/A N/A N/A N/A N/A 0000 0000 0000 0000 0000 0000 0000 0000 0111 1111 1100 1001 0111 1111 0111 1111 0111 1111 N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A 1101 0011 1010 1101 FUNCTION Read Internal Temperature Read External Temperature 1 Read Status Byte; Note 1 Read Configuration Byte Read Conversion Rate Byte Read Internal ALERT High Limit Read Internal ALERT Low Limit Read External Temperature 1 ALERT High Limit Read External Temperature 1 ALERT Low Limit Write Configuration Byte Write Conversion Rate Control Byte Write Internal ALERT High Limit Write Internal ALERT Low Limit Write External Temperature 1 ALERT High Limit Write External Temperature 1 ALERT Low Limit Read External 1 Extended Temperature Read External 2 Extended Temperature Read Internal Extended Temperature Read External Temperature 2 Read External Temperature 2 ALERT High Limit Read External Temperature 2 ALERT Low Limit Read Internal OVERT Limit Read External 1 OVERT Limit Read External 2 OVERT Limit Write Internal OVERT Limit Write External 1 OVERT Limit Write External 2 OVERT Limit Write External Temperature 2 ALERT High Limit Write External Temperature 2 ALERT Low Limit Write VCC (VIN2) ALERT High Limit for MAX6655 (MAX6656) Write VCC (VIN2) ALERT Low Limit for MAX6655 (MAX6656) Write VIN1 ALERT High Limit Write VIN1 ALERT Low Limit Write VIN2 (VCC) ALERT High Limit for MAX6655 (MAX6656) Write VIN2 (VCC) ALERT Low Limit for MAX6655 (MAX6656) Write VIN3 ALERT High Limit Write VIN3 ALERT Low Limit Read VCC (VIN2) ALERT High Limit for MAX6655 (MAX6656) Read VCC (VIN2) ALERT Low Limit for MAX6655 (MAX6656)
MAX6655/MAX6656
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Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors MAX6655/MAX6656
Table 6. Command Byte Register Map (continued)
REGISTER RV1HL RV1LL RV2HL RV2LL RV3HL RV3LL RV0 RV1 RV2 RV3 RSL2 RCL2 WCA2 RDID RDRV ADDRESS 28h 29h 2Ah 2Bh 2Ch 2Dh 2Eh 2Fh 30h 31h 32h 33h 34h FEh FFh POR STATE 1101 0011 1010 1101 1101 0011 1010 1101 1101 0011 1010 1101 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 N/A 0000 1010 0100 1101 FUNCTION Read VIN1 ALERT High Limit Read VIN1 ALERT Low Limit Read VIN2 (VCC) ALERT High Limit for MAX6655 (MAX6656) Read VIN2 (VCC) ALERT Low Limit for MAX6655 (MAX6656) Read VIN3 ALERT High Limit Read VIN3 ALERT Low Limit Read VCC (VIN2) for MAX6655 (MAX6656) Read VIN1 Read VIN2 (VCC) for MAX6655 (MAX6656) Read VIN3 Read Status Byte 2 Read Configuration Byte 2 Write Configuration Byte 2 Read Device ID Read Manufacture ID
Note 1: Upon application of power, the ADC begins converting. The MSB of the Status Byte register indicates a conversion in progress. The Status Byte has a value of 80h during conversions and a value of 00h between conversions. Therefore, at power-on, the Status Byte alternates between 00h and 80h.
Table 7. Configuration Byte 1 Bit Assignments
BIT 7 (MSB) 6 5 4 3 2 1 0 NAME Mask All RUN/STOP Mask Remote Temperature 1 Mask Remote Temperature 2 Mask VIN3 Mask VIN2 Mask VIN1 Mask VCC POR STATE 0 0 0 0 0 0 0 0 FUNCTION Masks out all ALERT interrupts if high. Standby mode control bit; if high, the device immediately stops converting and enters standby mode. If low, the device enters normal conversion mode. High masks out OVERT and ALERT interrupts due to remote-diode 1. High masks out OVERT and ALERT interrupts due to remote-diode 2. High masks ALERT interrupts due to VIN3. High masks ALERT interrupts due to VIN2 (VCC) for MAX6655 (MAX6656). High masks ALERT interrupts due to VIN1. High masks ALERT interrupts due to VCC (VIN2) for MAX6655 (MAX6656).
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Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors MAX6655/MAX6656
Table 8. Configuration Byte 2-Bit Assignments
BIT NAME Disable Remote Temperature 1 Measurement Disable Remote Temperature 2 Measurement Disable Internal Temperature Measurement Disable VIN3 Measurement Disable VIN2 Measurement Disable VIN1 Measurement Disable VCC Measurement Reserved POR STATE 0 FUNCTION
7 (MSB)
If high, the remote temperature 1 measurement is disabled.
6
0
If high, the remote temperature 2 measurement is disabled.
5
0
If high, the internal temperature measurement is disabled.
4 3 2 1 0
0 0 0 0 0
If high, the input voltage VIN3 measurement is disabled. If high, the input voltage VIN2 (VCC) measurement is disabled for MAX6655 (MAX6656). If high, the input voltage VIN1 measurement is disabled. If high, the input voltage VCC (VIN2) measurement is disabled for MAX6655 (MAX6656). Reserved for future use.
Table 9. Status Byte 1-Bit Assignments
BIT 7 (MSB) 6 5 4 3 2 1 0 NAME BUSY LHIGH LLOW RHIGH RLOW DODS1 R2HIGH R2LOW POR STATE 0 0 0 0 0 0 0 0 FUNCTION ADC is busy converting when high. Internal high-temperature ALERT has tripped when high; cleared by POR or readout of the entire Status Byte. Internal low-temperature ALERT has tripped when high; cleared by POR or readout of the entire Status Byte. External 1 high-temperature ALERT has tripped when high; cleared by POR or readout of the entire Status Byte. External 1 low-temperature ALERT has tripped when high; cleared by POR or readout of the entire Status Byte. A high indicates external diode 1 open/short. External 2 high-temperature ALERT has tripped when high; cleared by POR or readout of the entire Status Byte. External 2 low-temperature ALERT has tripped when high; cleared by POR or readout of the entire Status Byte.
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Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors MAX6655/MAX6656
Table 10. Status Byte 2-Bit Assignments
BIT 7(MSB) 6 5 4 3 2 1 0 NAME LO R1O R2O DODS2 VA3 VA2 VA1 VCCA POR STATE 0 0 0 0 0 0 0 0 FUNCTION Internal temperature has exceeded OVERT limit. Clear by falling below limit. External temperature 1 has exceeded OVERT limit. Clear by falling below limit. External temperature 2 has exceeded OVERT limit. Clear by falling below limit. A high indicates external diode 2 open or short. VIN3 out of window ALERT has tripped when high; cleared by POR or reading the Status Byte. VIN2 out of window ALERT has tripped when high; cleared by POR or reading the Status Byte. VIN1 out of window ALERT has tripped when high; cleared by POR or reading the Status Byte. VCC out of window ALERT has tripped when high; cleared by POR or reading the Status Byte.
Table 11. Remote-Sensor Transistor Manufacturers
MANUFACTURER Central Semiconductor (USA) Fairchild Semiconductor (USA) Infineon (Germany) ON Semiconductor (USA) Rohm Semiconductor (Japan) Zetex (England) MODEL NUMBER CMPT3906 MMBT3906 SMBT3906 MMBT3906 SST3906 FMMT3906CT-ND
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Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors
Typical Application Circuit
MAX6655/MAX6656
2.5V VCC CPU VCC DXP1 DXN1 TO 12V TO 3.3V OR 5V TO 2.5V VIN1 VIN2 VIN3 DXP2 MAX6655 MAX6656 SMBCLK SMBDATA ALERT OVERT ADD0 ADD1 DXN2 2N3906 2200pF GND TO SYSTEM SHUTDOWN 0.1F 10k SMBus/I2C CONTROLLER
Functional Diagram
VCC
MAX6655/MAX6656
VIN1 VIN2 VIN3 INPUT VOLTAGE SCALING AND MULTIPLEXER ADC DATA AND CONTROL LOGIC
DXP1 DXN1
TEMPERATURE SENSOR
VOLTAGE REFERENCE
SMBus/I2CCOMPATIBLE INTERFACE
SMBDATA SMBCLK ALERT OVERT
DXP2 DXN2
ADD0 ADD1
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Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors MAX6655/MAX6656
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.)
QSOP.EPS
PACKAGE OUTLINE, QSOP .150", .025" LEAD PITCH
21-0055
F
1 1
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
18 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2006 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.

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