19-2117; Rev 0; 7/01 Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors Applications Features ♦ 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, 0.125°C Resolution ♦ High Accuracy: ±1°C Over +60°C to +100°C 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 Ordering Information PART TEMP. RANGE PIN-PACKAGE MAX6655MEE -55°C to +125°C 16 QSOP MAX6656MEE -55°C to +125°C 16 QSOP Typical Application Circuit appears at end of data sheet. Pin Configuration TOP VIEW VCC 1 16 STBY Notebooks DXP1 2 15 SMBCLK Thin Clients DXN1 3 14 OVERT Servers ADD0 4 Workstations ADD1 5 Communication Equipment DXP2 6 11 VIN2 Desktop PC DXN2 7 10 VIN1 MAX6655 MAX6656 12 ALERT 9 GND 8 SMBus is a trademark of Intel Corp. 13 SMBDATA VIN3 QSOP I2C is a trademark of Philips Corp. ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX6655/MAX6656 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 ±1°C 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 SMBus™ 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. MAX6655/MAX6656 Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors ABSOLUTE MAXIMUM RATINGS DXN_ Current......................................................................±1mA ESD Protection (all pins, Human Body Model) ..................2000V Continuous Power Dissipation (TA = +70°C) 16-Pin QSOP (derate 8.30mW/°C above +70°C)........667mW Operating Temperature Range .........................-55°C to +125°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C 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 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 = -55°C to +125°C, unless otherwise noted. Typical values are at VCC = +3.3V for MAX6656, VCC = +5.0V for MAX6655, TA = +25°C.) PARAMETER Supply Range SYMBOL CONDITIONS VCC MIN 3.0 +60°C ≤ TA ≤ +100°C Accuracy (Local Sensor) ±1 ±3 VIN1, VIN2, VIN3 input resistance UVLO 11 Bits kΩ ±1 2.50 ±1.5 2.70 VCC, falling edge 1 POR Threshold Hysteresis 1.7 2.90 SMBus static, STBY = GND DXP and DXN Leakage Current In standby mode Average Operating Current Continuous temperature mode Conversion Time for Single Temperature Measurement tCON From stop bit to conversion completed Monitoring Cycle Time tMONI Total of 3 temperature plus 4 voltage measurements 3 95 V mV 2.5 90 Standby Current % Bits 90 Power-On Reset (POR) Threshold °C °C 8 VCC input, disables A/D conversion, falling edge °C 0.125 100 Undervoltage Lockout Hysteresis 2 V +60°C ≤ TRJ ≤ +100°C VIN ADC Resolution Undervoltage Lockout Threshold 5.5 0°C ≤ TRJ ≤ +120°C VIN1, VIN2, VIN3 between 30% and 120% of nominal ADC Total Error UNITS ±3 Temperature Measurement Resolution ZIN MAX ±1.5 0°C ≤ TA ≤ +125°C Accuracy (Remote Sensor) ADC Input Impedance TYP V mV 10 µA 2 µA 550 1000 µA 125 155 ms 625 _______________________________________________________________________________________ ms Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors (VCC = +3.0V to +3.6V for MAX6656, VCC = +4.5V to +5.5V for MAX6655, TA = -55°C to +125°C, unless otherwise noted. Typical values are at VCC = +3.3V for MAX6656, VCC = +5.0V for MAX6655, TA = +25°C.) PARAMETER SYMBOL Remote Junction Current (DXP, DXN) CONDITIONS MIN TYP MAX High level 80 100 140 Low level 8 10 14 UNITS µA SMBus INTERFACE (SMBCLK, SMBDATA, STBY) Logic Input Low Voltage Logic Input High Voltage Input Leakage Current VIL VIH ILEAK Output Low Sink Current IOL Input Capacitance CIN SMBus Timeout VCC = +3.0V to +5.5V 0.8 VCC = +3.0V 2.1 VCC = +5.5V 2.6 V V VIN = GND or VCC ±1 µA VOL = +0.6V 6 mA 5 SMBCLK or SMBDATA time low for reset 30 35 pF 60 ms ALERT, OVERT Output Low Sink Current VOL = +0.6V 6 mA Output High Leakage Current VOH = +5.5V 1 µA 400 kHz SMBus TIMING Serial Clock Frequency fSCL Bus Free Time Between STOP and START Condition tBUF START Condition Setup Time 4.7 µs 4.7 µs Repeat START Condition Setup Time tSU:STA 90% to 90% 50 ns START Condition Hold Time tHD:STA 10% of SMBDATA to 90% of SMBCLK 4 µs STOP Condition Setup Time tSU:STO 90% of SMBCLK to 10% of SMBDATA 4 Clock Low Period tLOW 10% to 10% Clock High Period tHIGH 90% to 90% Data Setup Time tSU:DAT 90% of SMBDATA to 10% of SMBCLK Data Hold Time tHD:DAT (Note 1) µs 4.7 µs 4 µs 250 ns 0 µs Receive SMBCLK/SMBDATA Rise Time tR 1 µs Receive SMBCLK/SMBDATA Fall Time tF 300 ns Pulse Width of Spike Suppressed tSP 50 ns 0 _______________________________________________________________________________________ 3 MAX6655/MAX6656 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) PATH = DXP TO VCC (5V) -10 3 2 1 0 -1 -2 20 MAX6655/MAX6656 toc03 RANDOM SAMPLE 2N3906 4 TEMPERATURE ERROR (°C) PATH = DXP TO GND 0 MAX6655/MAX6656 toc02 10 5 REMOTE TEMPERATURE ERROR (°C) MAX6655/MAX6656 toc01 REMOTE TEMPERATURE ERROR (°C) 20 TEMPERATURE ERROR vs. POWER-SUPPLY NOISE FREQUENCY REMOTE TEMPERATURE ERROR vs. REMOTE-DIODE TEMPERATURE REMOTE TEMPERATURE ERROR vs. PC BOARD RESISTANCE VIN = SQUARE WAVE APPLIED TO VCC WITH NO VCC BYPASS CAPACITOR 15 VIN = 250mVp-p REMOTE DIODE 10 5 -3 -4 0 -5 -55 100 -5 VIN = SQUARE WAVE AC-COUPLED TO DXN 10 8 VIN = 200mVp-p 6 4 VIN = 100mVp-p 2 10 20 30 40 40 STANDBY SUPPLY CURRENT vs. CLOCK FREQUENCY VCC = +5V 12 10 8 6 4 SMBCLK IS DRIVEN RAIL-TO-RAIL 45 40 35 30 25 20 15 10 5 0 0 50 100 150 200 1 10 100 1000 DXP-DXN CAPACITANCE (nF) SMBCLK FREQUENCY (kHz) STANDBY SUPPLY CURRENT vs. SUPPLY VOLTAGE RESPONSE TO THERMAL SHOCK VOLTAGE ACCURACY vs. TEMPERATURE 100 80 60 40 ADD0, ADD1 = HIGH-Z 100 80 60 40 20 20 0 0 REMOTE DIODE IMMERSED IN +115°C FLUORINERT BATH 12 OUTPUT VOLTAGE (V) ADD0, ADD1 = GND 120 TEMPERATURE (°C) 120 MAX6655/MAX6656 toc08 FREQUENCY (MHz) 140 50 50 2 50 MAX6655/MAX6656 toc07 0 30 REMOTE TEMPERATURE ERROR vs. DXP-DXN CAPACITANCE 0 0 20 MAX6655/MAX6656 toc09 12 10 FREQUENCY (MHz) 14 REMOTE TEMPERATURE ERROR (°C) MAX6655/MAX6656 toc04 REMOTE TEMPERATURE ERROR (°C) 14 0 95 TEMPERATURE (°C) LEAKAGE RESISTANCE (MΩ) REMOTE TEMPERATURE ERROR vs. COMMON-MODE NOISE FREQUENCY 45 MAX6655/MAX6656 toc06 10 SUPPLY CURRENT (µA) 1 MAX6655/MAX6656 toc05 -20 SUPPLY CURRENT (µA) MAX6655/MAX6656 Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors VIN1 10 8 6 VCC 4 VIN2 2 VIN3 INPUT VOLTAGES ARE NOMINAL 0 1 2 3 SUPPLY VOLTAGE (V) 4 4 5 0 -1 0 1 2 TIME (s) 3 4 5 0 20 40 60 80 TEMPERATURE (°C) _______________________________________________________________________________________ 100 120 Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors PIN NAME 1 VCC Supply Voltage. +5V for MAX6655; +3.3V for MAX6656. Bypass VCC to GND with a 0.1µF capacitor. FUNCTION 2 DXP1 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. 3 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. 4 ADD0 SMBus Slave Address Select Input. ADD0 and ADD1 are sampled upon power-up. Table 5 is the truth table. 5 ADD1 SMBus Slave Address Select Input. ADD0 and ADD1 are sampled upon power-up. 6 DXP2 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. 7 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. 8 GND Ground 9 VIN3 External Voltage Monitor 3. VIN3 is typically used to monitor +2.5V supplies. 10 VIN1 External Voltage Monitor 1. VIN1 is typically used to monitor +12V supplies. 11 VIN2 External Voltage Monitor 2. VIN2 is typically used to monitor voltage supplies of +3.3V for MAX6655 and +5.0V for MAX6656. 12 ALERT 13 SMBDATA 14 OVERT 15 SMBCLK 16 STBY 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. 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 +1/2°C error/Ω. A 200µV offset voltage at DXP-DXN causes about -1°C error. _______________________________________________________________________________________ 5 MAX6655/MAX6656 Pin Description MAX6655/MAX6656 Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors Write Byte Format S ADDRESS WR ACK COMMAND 7 bits ACK DATA 8 bits Slave Address: equivalent to chip-select line of a 3-wire interface ACK P 8 bits Command Byte: selects which register you are writing to Data Byte: data goes into the register set by the co mma nd byte ( to se t thresholds, configuration masks, and sampling rate) Read Byte Format S WR ADDRESS ACK 7 bits COMMAND ACK WR 7 bits Command Byte: selects which register you are reading from ACK DATA A P 8 bits Slave Address: repeated due to change in dataflow direction Data Byte: reads from the register set by the command byte Receive Byte Format ACK COMMAND ACK P 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 RD 7 bits Send Byte Format ADDRESS ADDRESS 8 bits Slave Address: equivalent to chip-select line S S Shaded = Slave transmission A = Not acknowledged S ADDRESS 7 bits RD ACK DATA A P 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 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 3µA (typ). Enter standby mode by forcing STBY low or through the RUN/STOP bit in the 6 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 550µA. Between conversions, the instantaneous supply current is about 25µA, 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. _______________________________________________________________________________________ Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors tLOW B C tHIGH D E F G I H J K L MAX6655/MAX6656 A M SMBCLK SMBDATA tHD:STA tSU:STA tSU:DAT 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 tHD:DAT tSU:STO tBUF J = ACKNOWLEDGE CLOCKED INTO SLAVE K = ACKNOWLEDGE CLOCK PULSE L = STOP CONDITION M = NEW START CONDITION 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 Figure 2. SMBus/I2C Write Timing Diagram A tLOW B C tHIGH D E F G H I J K L M SMBCLK SMBDATA tSU:STA tHD:STA tSU:DAT 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 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 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. _______________________________________________________________________________________ 7 MAX6655/MAX6656 Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors the T HIGH or T LOW alarms at their POR settings. Similarly, if DXP_ is short circuited to VCC, the ADC reads -1°C for both remote channels, and the ALERT outputs are activated. +3V TO +5.5V Alert Interrupts VCC MAX6655 MAX6656 SMBCLK SMBus SERIAL INTERFACE (TO HOST) SMBDATA TO SYSTEM SHUTDOWN ALERT OVERT DXP2 ADD0 ADD1 DXN2 2N3906 GND 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 1°C. Additionally, the 3MSBs of the Extended Temperature register contain fractional temperature data with +0.125°C resolution (Tables 2 and 3). The voltage data is stored in RV0, RV1, RV2, and RV3 as 8 bits in binary form (Table 4). 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 8 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. 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. 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. _______________________________________________________________________________________ Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors 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 10µA at the highest expected temperature. The forward voltage must be less than 0.95V at 100µA at the lowest expect- ed temperature. The base resistance has to be less than 100Ω. 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. 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 550µA + 0.4V x 1mA. Package θJA is about 150°C/W, so with VCC = +5V and no copper PC board heat sinking, the resulting temperature rise is: ∆T = 3.1mW x 150°C/W = +0.46°C Even with these contrived circumstances, it is difficult to introduce significant self-heating errors. 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 _______________________________________________________________________________________ 9 MAX6655/MAX6656 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 +127°C). The POR state of the TLOW register is 1100 1001 or -55°C. MAX6655/MAX6656 Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors 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 +30°C 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 20mΩ leakage path from DXP to ground causes approximately +1°C 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 3µV/°C, and it takes approximately 200µV of voltage error at DXP-DXN to cause a 1°C 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 10 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 1Ω series resistance introduces about +1/2°C error. Chip Information TRANSISTOR COUNT: 26,783 PROCESS: BiCMOS ______________________________________________________________________________________ Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors Table 3. Extended Resolution Register DATA (RCRA, 04H) WAIT TIME BETWEEN CONVERSION SEQUENCES (s) FRACTIONAL TEMPERATURE (°C) DIGITAL OUTPUT 0 0000 0000 0.125 0010 0000 00h 0 0.250 0100 0000 01h 0.125 0.375 0110 0000 02h 0.250 0.500 1000 0000 03h 0.500 0.625 1010 0000 04h 1.000 0.750 1100 0000 05h 2.000 0.875 1110 0000 06h 4.000 07h 4.000 Table 2. Temperature Data Format TEMP. (°C) ROUNDED TEMP. (°C) DIGITAL OUTPUT 130.00 +127 0 111 1111 127.00 +127 0 111 1111 126.00 +126 0 111 1111 25.25 +25 0 001 1001 0.50 +1 0 000 0001 0 0 0 000 0000 -0.625 -1 1 111 1111 -65 -65 1 011 1111 Diode Fault (Short or Open) — 1111 1111 ______________________________________________________________________________________ 11 MAX6655/MAX6656 Table 1. Conversion Rate Control Byte MAX6655/MAX6656 Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors Table 4. Voltage Data Format ADC OUTPUT CODE INPUT VOLTAGE AT VIN1 (+12V) INPUT VOLTAGE AT VIN2 (+5V) OR VCC INPUT VOLTAGE AT VIN2 (+3.3V) OR VCC INPUT VOLTAGE AT VIN3 (+2.5V) LSB weight 57.1mV 23.8mV 15.7mV 11.9mV 64 (≈ 1/4 scale) 4.343V to 4.400V 1.810V to 1.833V 1.194V to 1.210V 0.905V to 0.917V 65 4.400V to 4.457V 1.833V to 1.857V 1.210V to 1.226V 0.917V to 0.929V 66 4.457V to 4.514V 1.857V to 1.881V 1.226V to 1.242V 0.929V to 0.941V — — — — — 128 (≈ 1/2 scale) 8.000V to 8.057V 3.333V to 3.357V 2.200V to 2.216V 1.250V to 1.262V — — — — — 198 (≈ 3/4 scale) 12.000V to 12.057V 5.000V to 5.024V 3.300V to 3.3157V 2.500V to 2.512V — — — — — 210 12.686V to 12.743V 5.286V to 5.310V 3.486V to 3.504V 2.643V to 2.655V 211 12.743V to 12.800V 5.310V to 5.333V 3.504V to 3.521V 2.655V to 2.667V — — — — — 237 (≈ 5/4 scale) 14.228V to 14.285V 5.929V to 5.952V 3.913V to 3.929V 2.964V to 2.976V Table 5. Address Map (ADD[1:0]) ADD0 12 ADD1 ADDRESS 0 0 0011 0000 0 High-Z 0011 0010 0 1 0011 0100 High-Z 0 0101 0010 High-Z High-Z 0101 0100 High-Z 1 0101 0110 1 0 1001 1000 1 High-Z 1001 1010 1 1 1001 1100 ______________________________________________________________________________________ Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors MAX6655/MAX6656 Table 6. Command Byte Register Map REGISTER RLTS ADDRESS 00h POR STATE 0000 0000 FUNCTION RRTE 01h 0000 0000 Read External Temperature 1 RSL 02h 0000 0000 Read Status Byte; Note 1 RCL 03h 0000 0000 Read Configuration Byte Read Internal Temperature RCRA 04h 0000 0010 Read Conversion Rate Byte RLHN 05h 0111 1111 Read Internal ALERT High Limit RLLI 06h 1100 1001 Read Internal ALERT Low Limit RRHI 07h 0111 1111 Read External Temperature 1 ALERT High Limit RRLS 08h 1100 1001 Read External Temperature 1 ALERT Low Limit WCA 09h N/A Write Configuration Byte WCRW 0Ah N/A Write Conversion Rate Control Byte WLHO 0Bh N/A Write Internal ALERT High Limit WLLM 0Ch N/A Write Internal ALERT Low Limit WRHA 0Dh N/A Write External Temperature 1 ALERT High Limit Write External Temperature 1 ALERT Low Limit WRLN 0Eh N/A RRET1 10h 0000 0000 Read External 1 Extended Temperature RRET2 11h 0000 0000 Read External 2 Extended Temperature RLET 12h 0000 0000 Read Internal Extended Temperature RRT2 13h 0000 0000 Read External Temperature 2 RRHL2 14h 0111 1111 Read External Temperature 2 ALERT High Limit RRLL2 15h 1100 1001 Read External Temperature 2 ALERT Low Limit RLOL 16h 0111 1111 Read Internal OVERT Limit RLOL1 17h 0111 1111 Read External 1 OVERT Limit RLOL2 18h 0111 1111 WLOL 19h N/A Write Internal OVERT Limit WROL1 1Ah N/A Write External 1 OVERT Limit WROL2 1Bh N/A Write External 2 OVERT Limit WRH2 1Ch N/A Write External Temperature 2 ALERT High Limit WRL2 1Dh N/A Write External Temperature 2 ALERT Low Limit WV0HL 1Eh N/A Write VCC (VIN2) ALERT High Limit for MAX6655 (MAX6656) Write VCC (VIN2) ALERT Low Limit for MAX6655 (MAX6656) Read External 2 OVERT Limit WV0LL 1Fh N/A WV1HL 20h N/A Write VIN1 ALERT High Limit WV1LL 21h N/A Write VIN1 ALERT Low Limit WV2HL 22h N/A Write VIN2 (VCC) ALERT High Limit for MAX6655 (MAX6656) WV2LL 23h N/A Write VIN2 (VCC) ALERT Low Limit for MAX6655 (MAX6656) WV3HL 24h N/A Write VIN3 ALERT High Limit Write VIN3 ALERT Low Limit WV3LL 25h N/A RV0HL 26h 1101 0011 Read VCC (VIN2) ALERT High Limit for MAX6655 (MAX6656) RV0LL 27h 1010 1101 Read VCC (VIN2) ALERT Low Limit for MAX6655 (MAX6656) ______________________________________________________________________________________ 13 MAX6655/MAX6656 Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors Table 6. Command Byte Register Map (continued) REGISTER ADDRESS POR STATE RV1HL 28h 1101 0011 Read VIN1 ALERT High Limit FUNCTION RV1LL 29h 1010 1101 Read VIN1 ALERT Low Limit RV2HL 2Ah 1101 0011 Read VIN2 (VCC) ALERT High Limit for MAX6655 (MAX6656) RV2LL 2Bh 1010 1101 Read VIN2 (VCC) ALERT Low Limit for MAX6655 (MAX6656) RV3HL 2Ch 1101 0011 Read VIN3 ALERT High Limit RV3LL 2Dh 1010 1101 Read VIN3 ALERT Low Limit RV0 2Eh 0000 0000 Read VCC (VIN2) for MAX6655 (MAX6656) RV1 2Fh 0000 0000 Read VIN1 RV2 30h 0000 0000 Read VIN2 (VCC) for MAX6655 (MAX6656) RV3 31h 0000 0000 Read VIN3 RSL2 32h 0000 0000 Read Status Byte 2 Read Configuration Byte 2 RCL2 33h 0000 0000 WCA2 34h N/A RDID FEh 0000 1010 Read Device ID RDRV FFh 0100 1101 Read Manufacture ID Write Configuration Byte 2 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 14 BIT NAME POR STATE 7 (MSB) Mask All 0 Masks out all ALERT interrupts if high. 6 RUN/STOP 0 Standby mode control bit; if high, the device immediately stops converting and enters standby mode. If low, the device enters normal conversion mode. 5 Mask Remote Temperature 1 0 High masks out ALERT interrupts due to remote-diode 1. 4 Mask Remote Temperature 2 0 High masks out ALERT interrupts due to remote-diode 2. 3 Mask VIN3 0 High masks ALERT interrupts due to VIN3. 2 Mask VIN2 0 High masks ALERT interrupts due to VIN2 (VCC) for MAX6655 (MAX6656). 1 Mask VIN1 0 High masks ALERT interrupts due to VIN1. 0 Mask VCC 0 High masks ALERT interrupts due to VCC (VIN2) for MAX6655 (MAX6656). FUNCTION ______________________________________________________________________________________ Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors MAX6655/MAX6656 Table 8. Configuration Byte 2 Bit Assignments BIT NAME POR STATE 7 (MSB) Disable Remote Temperature 1 Measurement 0 If high, the remote temperature 1 measurement is disabled. 6 Disable Remote Temperature 2 Measurement 0 If high, the remote temperature 2 measurement is disabled. 5 Disable Internal Temperature Measurement 0 If high, the internal temperature measurement is disabled. 4 Disable VIN3 Measurement 0 If high, the input voltage VIN3 measurement is disabled. 3 Disable VIN2 Measurement 0 If high, the input voltage VIN2 (VCC) measurement is disabled for MAX6655 (MAX6656). 2 Disable VIN1 Measurement 0 If high, the input voltage VIN1 measurement is disabled. 1 Disable VCC Measurement 0 If high, the input voltage VCC (VIN2) measurement is disabled for MAX6655 (MAX6656). 0 Reserved 0 Reserved for future use. FUNCTION Table 9. Status Byte 1 Bit Assignments BIT NAME POR STATE 7 (MSB) BUSY 0 ADC is busy converting when high. FUNCTION 6 LHIGH 0 Internal high-temperature ALERT has tripped when high; cleared by POR or readout of the entire Status Byte. 5 LLOW 0 Internal low-temperature ALERT has tripped when high; cleared by POR or readout of the entire Status Byte. 4 RHIGH 0 External 1 high-temperature ALERT has tripped when high; cleared by POR or readout of the entire Status Byte. 3 RLOW 0 External 1 low-temperature ALERT has tripped when high; cleared by POR or readout of the entire Status Byte. 2 DODS1 0 A high indicates external diode 1 open/short. 1 R2HIGH 0 External 2 high-temperature ALERT has tripped when high; cleared by POR or readout of the entire Status Byte. 0 R2LOW 0 External 2 low-temperature ALERT has tripped when high; cleared by POR or readout of the entire Status Byte. ______________________________________________________________________________________ 15 MAX6655/MAX6656 Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors Table 10. Status Byte 2 Bit Assignments BIT NAME POR STATE 7(MSB) LO 0 Internal temperature has exceeded OVERT limit. Clear by falling below limit. FUNCTION 6 R1O 0 External temperature 1 has exceeded OVERT limit. Clear by falling below limit. 5 R2O 0 External temperature 2 has exceeded OVERT limit. Clear by falling below limit. 4 DODS2 0 A high indicates external diode 2 open or short. 3 VA3 0 VIN3 out of window ALERT has tripped when high; cleared by POR or reading the Status Byte. 2 VA2 0 VIN2 out of window ALERT has tripped when high; cleared by POR or reading the Status Byte. 1 VA1 0 VIN1 out of window ALERT has tripped when high; cleared by POR or reading the Status Byte. 0 VCCA 0 VCC out of window ALERT has tripped when high; cleared by POR or reading the Status Byte. Table 11. Remote-Sensor Transistor Manufacturers MANUFACTURER MODEL NUMBER Central Semiconductor (USA) CMPT3906 Fairchild Semiconductor (USA) MMBT3906 Infineon (Germany) SMBT3906 ON Semiconductor (USA) MMBT3906 Rohm Semiconductor (Japan) Zetex (England) 16 SST3906 FMMT3906CT-ND ______________________________________________________________________________________ Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors 2.5V VCC CPU VCC DXP1 TO 12V TO 3.3V OR 5V TO 2.5V 0.1µF 10kΩ MAX6655 MAX6656 DXN1 SMBCLK VIN1 SMBDATA VIN2 ALERT VIN3 OVERT DXP2 ADD0 SMBus/I2C CONTROLLER TO SYSTEM SHUTDOWN ADD1 DXN2 2N3906 GND 2200pF Functional Diagram VCC MAX6655/MAX6656 VIN1 VIN2 VIN3 DXP1 DXN1 INPUT VOLTAGE SCALING AND MULTIPLEXER ADC TEMPERATURE SENSOR VOLTAGE REFERENCE DXP2 DXN2 DATA AND CONTROL LOGIC SMBus/I2CCOMPATIBLE INTERFACE SMBDATA SMBCLK ALERT OVERT ADD0 ADD1 ______________________________________________________________________________________ 17 MAX6655/MAX6656 Typical Application Circuit Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors QSOP.EPS MAX6655/MAX6656 Package Information 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 © 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.