19-3183; Rev 3; 4/11 Dual Remote/Local Temperature Sensors with SMBus Serial Interface The MAX6695/MAX6696 are precise, dual-remote, and local digital temperature sensors. They accurately measure the temperature of their own die and two remote diode-connected transistors, and report the temperature in digital form on a 2-wire serial interface. The remote diode is typically the emitter-base junction of a common-collector PNP on a CPU, FPGA, GPU, or ASIC. The 2-wire serial interface accepts standard system management bus (SMBus) commands such as Write Byte, Read Byte, Send Byte, and Receive Byte to read the temperature data and program the alarm thresholds and conversion rate. The MAX6695/MAX6696 can function autonomously with a programmable conversion rate, which allows control of supply current and temperature update rate to match system needs. For conversion rates of 2Hz or less, the temperature is represented as 10 bits + sign with a resolution of +0.125°C. When the conversion rate is 4Hz, output data is 7 bits + sign with a resolution of +1°C. The MAX6695/ MAX6696 also include an SMBus timeout feature to enhance system reliability. Remote temperature sensing accuracy is ±1.5°C between +60°C and +100°C with no calibration needed. The MAX6695/MAX6696 measure temperatures from -40°C to +125°C. In addition to the SMBus ALERT output, the MAX6695/MAX6696 feature two overtemperature limit indicators (OT1 and OT2), which are active only while the temperature is above the corresponding programmable temperature limits. The OT1 and OT2 outputs are typically used for fan control, clock throttling, or system shutdown. The MAX6695 has a fixed SMBus address. The MAX6696 has nine different pin-selectable SMBus addresses. The MAX6695 is available in a 10-pin μMAX® and the MAX6696 is available in a 16-pin QSOP package. Both operate throughout the -40°C to +125°C temperature range. Features ♦ Measure One Local and Two Remote Temperatures ♦ 11-Bit, +0.125°C Resolution ♦ High Accuracy ±1.5°C (max) from +60°C to +100°C (Remote) ♦ ACPI Compliant ♦ Programmable Under/Overtemperature Alarms ♦ Programmable Conversion Rate ♦ Three Alarm Outputs: ALERT, OT1, and OT2 ♦ SMBus/I2C-Compatible Interface ♦ Compatible with 65nm Process Technology (Y Versions) Ordering Information PART TEMP RANGE MAX6695AUB+ -40°C to +125°C 10 μMAX PIN-PACKAGE MAX6695YAUB+ -40°C to +125°C 10 μMAX MAX6696AEE+ -40°C to +125°C 16 QSOP MAX6696YAEE+ -40°C to +125°C 16 QSOP Devices are also available in tape-and-reel packages. Specify tape and reel by adding “T” to the part number when ordering. +Denotes a lead(Pb)-free/RoHS-compliant package. Typical Operating Circuit 0.1μF 47Ω +3.3V 10kΩ EACH CPU DXP1 VCC SMBDATA SMBCLK Applications MAX6695 DXN Servers CLOCK ALERT INTERRUPT TO μP OT1 TO CLOCK THROTTLING OT2 TO SYSTEM SHUTDOWN Notebook Computers Desktop Computers DATA Workstations DXP2 Test and Measurement Equipment GND GRAPHICS PROCESSOR Typical Operating Circuits continued at end of data sheet. μMAX is a registered trademark of Maxim Integrated Products, Inc. Pin Configurations appear at end of data sheet. ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX6695/MAX6696 General Description MAX6695/MAX6696 Dual Remote/Local Temperature Sensors with SMBus Serial Interface ABSOLUTE MAXIMUM RATINGS VCC ...........................................................................-0.3V to +6V DXP1, DXP2................................................-0.3V to (VCC + 0.3V) DXN ......................................................................-0.3V to +0.8V SMBCLK, SMBDATA, ALERT ...................................-0.3V to +6V RESET, STBY, ADD0, ADD1, OT1, OT2 ...................-0.3V to +6V SMBDATA Current .................................................1mA to 50mA DXN Current ......................................................................±1mA Continuous Power Dissipation (TA = +70°C) 10-Pin μMAX (derate 6.9mW/°C above +70°C) ........555.6mW 16-Pin QSOP (derate 8.3mW/°C above +70°C) .......666.7mW Operating Temperature Range .........................-40°C to +125°C Junction Temperature .....................................................+150°C Storage Temperature Range ............................-65°C to +150°C Lead Temperature (soldering, 10s) ................................+300°C Soldering Temperature (reflow) .......................................+260°C 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, TA = 0°C to +125°C, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25°C) PARAMETER Supply Voltage SYMBOL CONDITIONS VCC MIN 3.0 Standby Supply Current SMBus static, ADC in idle state Operating Current Interface inactive, ADC active 0.5 Conversion rate = 0.125Hz Average Operating Current Remote Temperature Error (Note 1) mA Conversion rate = 4Hz 500 1000 TRJ = +25°C to +100°C (TA = +45°C to +85°C) -1.5 +1.5 TRJ = 0°C to +125°C (TA = +25°C to +100°C) -3.0 +3.0 TRJ = -40°C to +125°C (TA = 0°C to +125°C) -5.0 -2.0 +2.0 -3.0 +3.0 TA = 0°C to +125°C -4.5 +4.5 TA = -40°C to +125°C +3.0 TA = +45°C to +85°C -3.8 TA = +25°C to +100°C -4.0 TA = 0°C to +125°C -4.2 Falling edge of VCC disables ADC °C °C -4.4 1.3 1.45 1.6 2.2 2.8 2.95 V mV Channel 1 rate 4Hz, channel 2 / local rate 2Hz (conversion rate register 05h) 112.5 Channel 1 rate 8Hz, channel 2 / local rate 4Hz (conversion rate register 06h) 56.25 62.5 68.75 High level 80 100 120 Low level 8 10 12 125 V mV 90 IRJ °C +5.0 500 UVLO μA +3.0 TA = +25°C to +100°C VCC, falling edge (Note 2) Conversion Time 2 1 70 Undervoltage Lockout Hysteresis Remote-Diode Source Current μA 500 POR Threshold Hysteresis Undervoltage Lockout Threshold V 10 35 TA = -40°C to +125°C Power-On Reset Threshold UNITS 3.6 250 TA = +45°C to +85°C Local Temperature Error (MAX6695Y/MAX6696Y) MAX Conversion rate = 1Hz TRJ = -40°C to +125°C (TA = -40°C) Local Temperature Error TYP 137.5 ms _______________________________________________________________________________________ μA Dual Remote/Local Temperature Sensors with SMBus Serial Interface (VCC = +3.0V to +3.6V, TA = 0°C to +125°C, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25°C) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS ALERT, OT1, OT2 Output Low Sink Current VOL = 0.4V 6 mA Output High Leakage Current VOH = 3.6V 1 μA 0.3 V INPUT PIN, ADD0, ADD1 (MAX6696) Logic Input Low Voltage VIL Logic Input High Voltage VIH 2.9 V INPUT PIN, RESET, STBY (MAX6696) Logic Input Low Voltage VIL Logic Input High Voltage VIH 2.1 ILEAK -1 Input Leakage Current 0.8 V +1 μA 0.8 V ±1 μA 6 mA V 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 2.1 V VIN = GND or VCC VOL = 0.6V 5 pF SMBus-COMPATIBLE TIMING (Figures 4 and 5) (Note 2) Serial Clock Frequency f SCL 10 Bus Free Time Between STOP and START Condition tBUF 4.7 μs Repeat START Condition Setup Time t SU:STA 4.7 μs 90% of SMBCLK to 90% of SMBDATA 100 kHz START Condition Hold Time tHD:STA 10% of SMBDATA to 90% of SMBCLK 4 μs STOP Condition Setup Time t SU:STO 90% of SMBCLK to 90% of SMBDATA 4 μs μs Clock Low Period tLOW 10% to 10% 4 Clock High Period tHIGH 90% to 90% 4.7 μs ns Data Setup Time t SU:DAT 250 Data Hold Time tHD:DAT 300 SMB Rise Time tR 1 μs SMB Fall Time tF 300 ns 40 ms SMBus Timeout SMBDATA low period for interface reset 20 ns 30 Note 1: Based on diode ideality factor of 1.008. Note 2: Specifications are guaranteed by design, not production tested. _______________________________________________________________________________________ 3 MAX6695/MAX6696 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VCC = 3.3V, TA = +25°C, unless otherwise noted.) AVERAGE OPERATING SUPPLY CURRENT vs. CONVERSION RATE CONTROL REGISTER VALUE 3 2 1 500 4 TEMPERATURE ERROR (°C) 4 5 MAX6695 toc02 5 600 OPERATING SUPPLY CURRENT (μA) MAX6695 toc01 STANDBY SUPPLY CURRENT (μA) 6 TEMPERATURE ERROR vs. REMOTE-DIODE TEMPERATURE 400 300 200 MAX6695 toc03 STANDBY SUPPLY CURRENT vs. SUPPLY VOLTAGE 3 REMOTE CHANNEL1 2 1 0 -1 REMOTE CHANNEL2 -2 100 -3 0 -5 -4 0 3.1 3.2 3.3 3.4 3.5 1 2 3 4 5 6 7 -50 -25 0 25 50 75 100 125 CONVERSION RATE CONTROL REGISTER VALUE (hex) REMOTE TEMPERATURE (°C) LOCAL TEMPERATURE ERROR vs. DIE TEMPERATURE TEMPERATURE ERROR vs. DXP-DXN CAPACITANCE TEMPERATURE ERROR vs. DIFFERENTIAL NOISE FREQUENCY 2 TEMPERATURE ERROR (°C) 3 2 1 0 -1 -2 -3 REMOTE CHANNEL2 1 0 REMOTE CHANNEL1 -1 VIN = 10mVP-P REMOTE CHANNEL2 2 TEMPERATURE ERROR (°C) 4 3 MAX6695 toc06 3 MAX6695 toc04 5 TEMPERATURE ERROR (°C) 0 3.6 SUPPLY VOLTAGE (V) MAX6695 toc05 3.0 1 0 REMOTE CHANNEL1 -1 -2 -2 -4 -5 -25 0 25 50 75 100 125 1 10 0.001 100 0.01 0.1 1 10 100 DIE TEMPERATURE (°C) DXP-DXN CAPACITANCE (nF) FREQUENCY (MHz) REMOTE TEMPERATURE ERROR vs. POWER-SUPPLY NOISE FREQUENCY LOCAL TEMPERATURE ERROR vs. POWER-SUPPLY NOISE FREQUENCY TEMPERATURE ERROR vs. COMMON-MODE NOISE FREQUENCY REMOTE CHANNEL2 1 0 REMOTE CHANNEL1 -1 2 1 0 -1 -2 -2 0.001 0.01 0.1 1 FREQUENCY (MHz) 10 100 10mVP-P 2 REMOTE CHANNEL2 1 0 REMOTE CHANNEL1 -1 -2 -3 -3 3 MAX6695 toc08 100mVP-P TEMPERATURE ERROR (°C) 2 3 MAX6695 toc07b 100mVP-P TEMPERATURE ERROR (°C) MAX6695 toc07a 3 4 -3 -3 -50 TEMPERATURE ERROR (°C) MAX6695/MAX6696 Dual Remote/Local Temperature Sensors with SMBus Serial Interface -3 0.001 0.01 0.1 1 FREQUENCY (MHz) 10 100 0.001 0.01 0.1 1 FREQUENCY (Hz) _______________________________________________________________________________________ 10 100 Dual Remote/Local Temperature Sensors with SMBus Serial Interface PIN MAX6695 MAX6696 1 2 NAME FUNCTION VCC Supply Voltage Input, +3V to +3.6V. Bypass to GND with a 0.1μF capacitor. A 47 series resistor is recommended but not required for additional noise filtering. See Typical Operating Circuit. 2 3 DXP1 Combined Remote-Diode Current Source and A/D Positive Input for Remote-Diode Channel 1. DO NOT LEAVE DXP1 UNCONNECTED; connect DXP1 to DXN if no remote diode is used. Place a 2200pF capacitor between DXP1 and DXN for noise filtering. 3 4 DXN Combined Remote-Diode Current Sink and A/D Negative Input. DXN is internally biased to one diode drop above ground. 4 5 DXP2 Combined Remote-Diode Current Source and A/D Positive Input for Remote-Diode Channel 2. DO NOT LEAVE DXP2 UNCONNECTED; connect DXP2 to DXN if no remote diode is used. Place a 2200pF capacitor between DXP2 and DXN for noise filtering. 5 10 OT1 Overtemperature Active-Low Output, Open Drain. OT1 is asserted low only when the temperature is above the programmed OT1 threshold. 6 8 GND Ground 7 9 SMBCLK SMBus Serial-Clock Input SMBus Alert (Interrupt) Active-Low Output, Open-Drain. Asserts when temperature exceeds user-set limits (high or low temperature) or when a remote sensor opens. Stays asserted until acknowledged by either reading the status register or by successfully responding to an alert response address. See the ALERT Interrupts section. 8 11 ALERT 9 12 SMBDATA 10 13 OT2 Overtemperature Active-Low Output, Open Drain. OT2 is asserted low only when temperature is above the programmed OT2 threshold. — 1, 16 N.C. No Connect — 6 ADD1 SMBus Slave Address Select Input (Table 10). ADD0 and ADD1 are sampled upon power-up. — 7 RESET Reset Input. Drive RESET high to set all registers to their default values (POR state). Pull RESET low for normal operation. — 14 ADD0 SMBus Slave Address Select Input (Table 10). ADD0 and ADD1 are sampled upon power-up. — 15 STBY Hardware Standby Input. Pull STBY low to put the device into standby mode. All registers’ data are maintained. SMBus Serial-Data Input/Output, Open Drain _______________________________________________________________________________________ 5 MAX6695/MAX6696 Pin Description MAX6695/MAX6696 Dual Remote/Local Temperature Sensors with SMBus Serial Interface Detailed Description The MAX6695/MAX6696 are temperature sensors designed to work in conjunction with a microprocessor or other intelligence in temperature monitoring, protection, or control applications. Communication with the MAX6695/MAX6696 occurs through the SMBus serial interface and dedicated alert pins. The overtemperature alarms OT1 and OT2 are asserted if the softwareprogrammed temperature thresholds are exceeded. OT1 and OT2 can be connected to a fan, system shutdown, or other thermal-management circuitry. The MAX6695/MAX6696 convert temperatures to digital data continuously at a programmed rate or by selecting a single conversion. At the highest conversion rate, temperature conversion results are stored in the “main” temperature data registers (at addresses 00h and 01h) as 7-bit + sign data with the LSB equal to +1°C. At slower conversion rates, 3 additional bits are available at addresses 11h and 10h, providing +0.125°C resolution. See Tables 2, 3, and 4 for data formats. ADC and Multiplexer The MAX6695/MAX6696 averaging ADC (Figure 1) integrates over a 62.5ms or 125ms period (each channel, typ), depending on the conversion rate (see Electrical Characteristics table). The use of an averaging ADC attains excellent noise rejection. The MAX6695/MAX6696 multiplexer (Figure 1) automatically steers bias currents through the remote and local diodes. The ADC and associated circuitry measure each diode’s forward voltages and compute the temperature based on these voltages. If a remote channel is not used, connect DXP_ to DXN. Do not leave DXP_ and DXN unconnected. When a conversion is initiated, all channels are converted whether they are used or not. The DXN input is biased at one VBE above ground by an internal diode to set up the ADC inputs for a differential measurement. Resistance in series with the remote diode causes about +1/2°C error per ohm. A/D Conversion Sequence A conversion sequence consists of a local temperature measurement and two remote temperature measurements. Each time a conversion begins, whether initiated automatically in the free-running autoconvert mode (RUN/STOP = 0) or by writing a one-shot command, all three channels are converted, and the results of the three measurements are available after the end of conversion. Because it is common to require temperature measurements to be made at a faster rate on one of the remote channels than on the other two channels, the conversion sequence is Remote 1, Local, Remote 1, Remote 2. Therefore, the Remote 1 conversion rate is 6 double that of the conversion rate for either of the other two channels. A BUSY status bit in status register 1 (see Table 7 and the Status Byte Functions section) shows that the device is actually performing a new conversion. The results of the previous conversion sequence are always available when the ADC is busy. Remote-Diode Selection The MAX6695/MAX6696 can directly measure the die temperature of CPUs and other ICs that have on-board temperature-sensing diodes (see the Typical Operating Circuit) or they can measure the temperature of a discrete diode-connected 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 MAX6695/MAX6696 (not the MAX6695Y/MAX6696Y) are optimized for n = 1.008. A thermal diode on the substrate of an IC is normally a PNP with its collector 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 1.008 is used, the output data will be 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 = T ACTUAL × ⎜ ⎟ ⎝ nNOMINAL ⎠ where temperature is measured in Kelvin and nNOMIMAL for the MAX6695/MAX6696 is 1.008. As an example, assume you want to use the MAX6695 or MAX6696 with a CPU that has an ideality factor of 1.002. If the diode has no series resistance, the measured data is related to the real temperature as follows: ⎛n ⎞ ⎛ 1. 008 ⎞ = TM × (1. 00599 ) T ACTUAL = TM × ⎜ NOMINAL ⎟ = TM × ⎜ ⎝ 1. 002 ⎟⎠ n1 ⎝ ⎠ For a real temperature of +85°C (358.15K), the measured temperature is +82.87°C (356.02K), an error of -2.13°C. Effect of Series Resistance Series resistance (RS) with a sensing diode contributes additional error. For nominal diode currents of 10μA _______________________________________________________________________________________ Dual Remote/Local Temperature Sensors with SMBus Serial Interface MAX6695/MAX6696 VCC (RESET) RESET/ UVLO CIRCUITRY 3 DXP1 MUX DXN DXP2 REMOTE1 REMOTE2 CONTROL LOGIC ADC LOCAL DIODE FAULT ALERT (STBY) SMBus S Q 8 READ SMBDATA 8 WRITE SMBCLK R REGISTER BANK 7 COMMAND BYTE REMOTE TEMPERATURES OT1 Q S (ADD0) ADDRESS DECODER (ADD1) LOCAL TEMPERATURES R ALERT THRESHOLD ALERT RESPONSE ADDRESS OT2 OT1 THRESHOLDS Q S R OT2 THRESHOLDS () ARE FOR MAX6696 ONLY. Figure 1. MAX6695/MAX6696 Functional Diagram and 100μA, the change in the measured voltage due to series resistance is: ΔVM = (100μ A − 10μ A) × R S = 90μ A × R S Since 1°C corresponds to 198.6μV, series resistance contributes a temperature offset of: μV 90 Ω = 0 . 453 °C μV Ω 198 . 6 °C Assume that the sensing diode being measured has a series resistance of 3Ω. The series resistance contributes a temperature offset of: °C 3Ω × 0. 453 = + 1 . 36 °C Ω The effects of the ideality factor and series resistance are additive. If the diode has an ideality factor of 1.002 and series resistance of 3Ω, the total offset can be calculated by adding error due to series resistance with error due to ideality factor: 1.36°C - 2.13°C = -0.77°C for a diode temperature of +85°C. _______________________________________________________________________________________ 7 MAX6695/MAX6696 Dual Remote/Local Temperature Sensors with SMBus Serial Interface In this example, the effect of the series resistance and the ideality factor partially cancel each other. Discrete Remote Diodes When the remote-sensing diode is a discrete transistor, its collector and base must be connected together. Table 1 lists examples of discrete transistors that are appropriate for use with the MAX6695/MAX6696. The transistor must be a small-signal type with a relatively high forward voltage; otherwise, the A/D input voltage range can be violated. The forward voltage at the highest expected temperature must be greater than 0.25V at 10μA, and at the lowest expected temperature, the forward voltage must be less than 0.95V at 100μA. Large power transistors must not be used. Also, ensure that the base resistance is less than 100Ω. Tight specifications for forward current gain (50 < ß <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 ±2°C 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. Thermal Mass and Self-Heating When sensing local temperature, these temperature sensors are intended to measure the temperature of the PC board to which they are soldered. The leads provide a good thermal path between the PC board traces and the die. 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 PC board is far greater than that of the MAX6695/ MAX6696, the device follows temperature changes on the PC board with little or no perceivable delay. When measuring the temperature of a CPU or other IC with an on-chip sense junction, thermal mass has virtually no effect; the measured temperature of the junction tracks the actual temperature within a conversion cycle. 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 8 Table 1. Remote-Sensor Transistor Manufacturers MANUFACTURER MODEL NO. Central Semiconductor (USA) CMPT3904 Rohm Semiconductor (USA) SST3904 Samsung (Korea) KST3904-TF Siemens (Germany) SMBT3904 Zetex (England) FMMT3904CT-ND Note: Discrete transistors must be diode connected (base shorted to collector). that stray air currents across the sensor package do not interfere with measurement accuracy. Self-heating does not significantly affect measurement accuracy. Remote-sensor self-heating due to the diode current source is negligible. For local temperature measurements, the worst-case error occurs when autoconverting at the fastest rate and simultaneously sinking maximum current at the ALERT output. For example, with VCC = 3.6V, a 4Hz conversion rate and ALERT sinking 1mA, the typical power dissipation is: VCC × 500μ A + 0 . 4V × 1mA = 2 . 2mW θJ-A for the 16-pin QSOP package is about +120°C/W, so assuming no copper PC board heat sinking, the resulting temperature rise is: ΔT = 2. 2mW × 120 °C / W = + 0 . 264 °C Even under these worst-case circumstances, it is difficult to introduce significant self-heating errors. 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 2200pF capacitor between DXP_ and DXN. Larger capacitor values can be used for added filtering, but do not exceed 3300pF 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 PC board layout as discussed in the PC Board Layout section. Low-Power Standby Mode Standby mode reduces the supply current to less than 10μA by disabling the ADC. Enter hardware standby (MAX6696 only) by forcing STBY low, or enter software standby by setting the RUN/STOP bit to 1 in the config- _______________________________________________________________________________________ Dual Remote/Local Temperature Sensors with SMBus Serial Interface MAX6695/MAX6696 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 1 Data Byte: data goes into the register set by the command byte (to set thresholds, configuration masks, and sampling rate) Read Byte Format ADDRESS WR ACK 7 bits COMMAND ACK RD ACK 7 bits Command Byte: selects which register you are reading from Send Byte Format DATA /// 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 WR 7 bits ACK COMMAND ACK P 8 bits Command Byte: sends command with no data, usually used for one-shot command S = Start condition P = Stop condition ADDRESS 8 bits Slave Address: equivalent to chip-select line ADDRESS S Shaded = Slave transmission /// = Not acknowledged S ADDRESS 7 bits RD ACK DATA /// 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 2. SMBus Protocols uration byte register. Hardware and software standbys are very similar; all data is retained in memory, and the SMBus interface is alive and listening for SMBus commands but the SMBus timeout is disabled. The only difference is that in software standby mode, the one-shot command initiates a conversion. With hardware standby, the one-shot command is ignored. Activity on the SMBus causes the device to draw extra supply current. Driving STBY low overrides any software conversion command. If a hardware or software 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. SMBus Digital Interface From a software perspective, the MAX6695/MAX6696 appear as a series of 8-bit registers that contain temperature data, alarm threshold values, and control bits. A standard SMBus-compatible 2-wire serial interface is used to read temperature data and write control bits and alarm threshold data. The same SMBus slave address provides access to all functions. The MAX6695/MAX6696 employ 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. When the conversion rate control register is set ≥ 06h, temperature data can be read from the read internal temperature (00h) and read external temperature (01h) registers. The temperature data format in these registers is 7 bits + sign in two’s-complement form for each channel, with the LSB representing +1°C (Table 2). The MSB is transmitted first. Use bit 3 of the configuration register to select the registers corresponding to remote 1 or remote 2. When the conversion rate control register is set ≤ 05h, temperature data can be read from the read internal temperature (00h) and read external temperature (01h) registers, the same as for faster conversion rates. An additional 3 bits can be read from the read external extended temperature register (10h) and read internal _______________________________________________________________________________________ 9 MAX6695/MAX6696 Dual Remote/Local Temperature Sensors with SMBus Serial Interface extended temperature register (11h) (Table 3), which extends the temperature data to 10 bits + sign and the resolution to +0.125°C per LSB (Table 4). When a conversion is complete, the main register and the extended register are updated almost simultaneously. Ensure that no conversions are completed between reading the main and extended registers so that when data that is read, both registers contain the result of the same conversion. To ensure valid extended data, read extended resolution temperature data using one of the following approaches: • Put the MAX6695/MAX6696 into standby mode by setting bit 6 of the configuration register to 1. Read the contents of the data registers. Return to run mode by setting bit 6 to zero. • Put the MAX6695/MAX6696 into standby mode by setting bit 6 of the configuration register to 1. Initiate a one-shot conversion using Send Byte command 0Fh. When this conversion is complete, read the contents of the temperature data registers. Table 2. Data Format (Two’s Complement) TEMP (°C) DIGITAL OUTPUT +130.00 0 111 1111 +127.00 0 111 1111 +126.00 0 111 1110 +25.25 0 001 1001 +0.50 0 000 0001 0 0 000 0000 -1 1 111 1111 -55 1 100 1001 Diode fault (short or open) 1 000 0000 Table 3. Extended Resolution Register FRACTIONAL TEMPERATURE (°C) CONTENTS OF EXTENDED REGISTER 0 000X XXXX +0.125 001X XXXX +0.250 010X XXXX +0.375 011X XXXX +0.500 100X XXXX +0.625 101X XXXX +0.750 110X XXXX +0.875 111X XXXX Diode Fault Alarm There is a continuity fault detector at DXP_ that detects an open circuit between DXP_ and DXN, or a DXP_ short to VCC, GND, or DXN. If an open or short circuit exists, the external temperature register (01h) is loaded with 1000 0000. Bit 2 (diode fault) of the status registers is correspondingly set to 1. The ALERT output asserts for open diode faults but not for shorted diode faults. Immediately after power-on reset (POR), the status register indicates that no fault is present until the end of the first conversion. After the conversion is complete, any diode fault is indicated in the appropriate status register. Reading the status register clears the diode fault bit in that register, and clears the ALERT output if set. If the diode fault is present after the next conversion, the status bit will again be set and the ALERT output will assert if the fault is an open diode fault. Alarm Threshold Registers Six registers, WLHO, WLLM, WRHA (1 and 2), and WRLN (1 and 2), store ALERT threshold values. WLHO and WLLM, are for internal ALERT high-temperature and low-temperature limits, respectively. Likewise, WRHA and WRLN are for external channel 1 and channel 2 high-temperature and low-temperature limits, respectively (Table 5). If either measured temperature equals or exceeds the corresponding ALERT threshold value, the ALERT output is asserted. The POR state of both internal and external ALERT high-temperature limit registers is 0100 0110 or +70°C. 10 Note: Extended resolution applies only for conversion rate control register values of 05h or less. Table 4. Data Format in Extended Mode TEMP (°C) INTEGER TEMP FRACTIONAL TEMP +130.00 0 111 1111 000X XXXX +127.00 0 111 1111 000X XXXX +126.5 0 111 1110 100X XXXX +25.25 0 001 1001 010X XXXX +0.50 0 000 0000 100X XXXX 0 0 000 0000 000X XXXX -1 1 111 1111 000X XXXX -1.25 1111 1111 010X XXXX -55 1100 1001 000X XXXX ______________________________________________________________________________________ Dual Remote/Local Temperature Sensors with SMBus Serial Interface MAX6695/MAX6696 Table 5. Command-Byte Register Bit Assignments REGISTER ADDRESS POR STATE FUNCTION RLTS 00 h 0000 0000 (0°C) Read internal temperature RRTE 01 h 0000 0000 (0°C) Read external channel 1 temperature if bit 3 of configuration register is 0; Read external channel 2 temperature if bit 3 of configuration register is 1 RSL1 02 h 1000 0000 Read status register 1 RCL 03 h 0000 0000 Read configuration byte (fault queue should be disabled at startup) RCRA 04 h 0000 0110 Read conversion rate byte RLHN 05 h 0100 0110 (+70°C) Read internal ALERT high limit RLLI 06 h 1100 1001 (-55°C) Read internal ALERT low limit RRHI 07 h 0100 0110 (+70°C) Read external channel 1 ALERT high limit if bit 3 of configuration register is 0; Read external channel 2 ALERT high limit if bit 3 of configuration register is 1 RRLS 08 h 1100 1001 (-55°C) Read external channel 1 ALERT low limit if bit 3 of configuration register is 0; Read external channel 2 ALERT low limit if bit 3 of configuration register is 1 WCA 09 h 0010 0000 Write configuration byte WCRW 0A h 0000 0110 Write conversion rate byte WLHO 0B h 0100 0110 (+70°C) Write internal ALERT high limit WLLM 0C h 1100 1001 (-55°C) Write internal ALERT low limit WRHA 0D h 0100 0110 (+70°C) Write external channel 1 ALERT high limit if bit 3 of configuration register is 0; Write external channel 2 ALERT high limit if bit 3 of configuration register is 1 WRLN 0E h 1100 1001 (-55°C) Write external channel 1 ALERT low limit if bit 3 of configuration register is 0; Write external channel 2 ALERT low limit if bit 3 of configuration register is 1 OSHT 0F h 0000 0000 One shot REET 10 h 0000 0000 Read extended temp of external channel 1 if bit 3 of configuration register is 0; Read extended temp of external channel 2 if bit 3 of configuration register is 1 RIET 11 h 0000 0000 Read internal extended temperature RSL2 12 h 0000 0000 Read status register 2 RWO2E 16 h 0111 1000 (+120°C) Read/write external OT2 limit for channel 1 if bit 3 of configuration register is 0; Read/write external OT2 limit for channel 2 if bit 3 of configuration register is 1 RWO2I 17 h 0101 1010 (+90°C) Read/write internal OT2 limit RWO1E 19 h 0101 1010 (+90°C) Read/write external OT1 limit for channel 1 if bit 3 of configuration register is 0; Read/write external OT1 limit for channel 2 if bit 3 of configuration register is 1 RWO1I 20 h 0100 0110 (+70°C) Read/write internal OT1 limit ______________________________________________________________________________________ 11 MAX6695/MAX6696 Dual Remote/Local Temperature Sensors with SMBus Serial Interface Table 5. Command-Byte Register Bit Assignments (continued) REGISTER ADDRESS POR STATE HYST 21 h 0000 1010 (10°C) RDID FE h 4D h FUNCTION Temperature hysteresis for OT1 and OT2 Read manufacturer ID The POR state of both internal and external ALERT lowtemperature limit registers is 1100 1001 or -55°C. Use bit 3 of the configuration register to select remote 1 or remote 2 when reading or writing remote thresholds. Additional registers, RWO1E, RWO1I, RWO2E, and RWO2I, store remote and local alarm threshold data information corresponding to the OT1 and OT2 outputs (See the OT1 and OT2 Overtemperature Alarms section.) ALERT Interrupt Mode An ALERT interrupt occurs when the internal or external temperature reading exceeds a high- or low-temperature limit (both limits are user programmable), or when the remote diode is disconnected (for continuity fault detection). The ALERT interrupt output signal is latched and can be cleared only by reading either of the status registers or by successfully responding to an Alert Response address. 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. The interrupt output pin is open drain so that multiple devices can share a common interrupt line. The interrupt rate never exceeds the conversion rate. Alert Response Address The SMBus Alert Response interrupt pointer provides quick fault identification for simple slave devices. Upon receiving an interrupt signal, the host master can broadcast a Receive Byte transmission to the Alert Response slave address (see Slave Addresses 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 acknowledgement 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 interrupt latch, provided the condition that caused the alert no longer exists. If the condition still 12 exists, the device reasserts the ALERT interrupt at the end of the next conversion. OT1 and OT2 Overtemperature Alarms Two registers, RWO1E and RWO1I, store remote and local alarm threshold data corresponding to the OT1 output. Two other registers, RWO2E and RWO2I, store remote and local alarm threshold data corresponding to the OT2 output. The values stored in these registers are high-temperature thresholds. The OT1 or OT2 output is asserted if any one of the measured temperatures equals or exceeds the corresponding alarm threshold value. OT1 and OT2 always operate in comparator mode and are asserted when the temperature rises above a value programmed in the appropriate threshold register. They are deasserted when the temperature drops below this threshold, minus the programmed value in the hysteresis HYST register (21h). 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. The HYST byte sets the amount of hysteresis to deassert both OT1 and OT2 outputs. The data format for the HYST byte is 7 bit + sign with +1°C resolution. Bit 7 of the HYST register should always be zero. OT1 responds immediately to temperature faults. OT2 activates either immediately or after four consecutive remote channel temperature faults, depending on the state of the fault queue bit (bit 5 of the configuration register). Command Byte Functions The 8-bit command byte register (Table 5) is the master index that points to the various other registers within the MAX6695/MAX6696. This register’s POR state is 0000 0000, so a Receive Byte transmission (a protocol that lacks the command byte) occurring immediately after POR returns the current local temperature data. One-Shot The one-shot command immediately forces a new conversion cycle to begin. If the one-shot command is received when the MAX6695/MAX6696 are in software standby mode (RUN/STOP bit = 1), a new conversion is ______________________________________________________________________________________ Dual Remote/Local Temperature Sensors with SMBus Serial Interface BIT NAME POR STATE 7(MSB) MASK1 0 Mask ALERT interrupts when 1. 6 RUN/STOP 0 Standby mode control bit. If 1, immediately stops converting and enters standby mode. If zero, it converts in either one-shot or timer mode. 5 Fault Queue 0 Fault queue enables when 1. When set to 1, four consecutive faults must occur before OT2 output is asserted. 4 RFU 0 Reserved. Remote 2 Select 0 0: Read/write remote 1 temperature and set-point values. 1: Read/write remote 2 temperature and set-point values. 2 SMB Timeout Disable 0 When set to 1, it disables the SMBus timeout, as well as the alert response. 1 MASK Alert Channel 2 0 When set to 1, it masks ALERT interrupt due to channel 2. 0 MASK Alert Channel 1 0 When set to 1, it masks ALERT interrupt due to channel 1. 3 FUNCTION begun, after which the device returns to standby mode. If a conversion is in progress when a one-shot command is received, the command is ignored. If a oneshot command is received in autoconvert mode (RUN/STOP bit = 0) between conversions, a new conversion begins, the conversion rate timer is reset, and the next automatic conversion takes place after a full delay elapses. Fault Queue Function To avoid false triggering of the MAX6695/MAX6696 in noisy environments, a fault queue is provided, which can be enabled by setting bit 5 (configuration register) to 1. Four channel 1 fault or two channel 2 fault events must occur consecutively before the fault output (OT2) becomes active. Any reading that breaks the sequence resets the fault queue counter. If there are three overlimit readings followed by a within-limit reading, the remote channel 1 fault queue counter is reset. Configuration Byte Functions The configuration byte register (Table 6) is a read-write register with several functions. Bit 7 is used to mask (disable) ALERT interrupts. Bit 6 puts the device into software standby mode (STOP) or autonomous (RUN) mode. Bit 5, when 1, enables the Fault Queue. Bit 4 is reserved. Bit 3 is used to select either remote channel 1 or remote channel 2 for reading temperature data or for setting or reading temperature limits. Bit 2 disables the SMBus timeout, as well as the Alert Response. Bit 1 masks ALERT interrupt due to channel 2 when high. Bit 0 masks ALERT interrupt due to channel 1 when high. Status Byte Functions The status registers (Tables 7 and 8) indicate which (if any) temperature thresholds have been exceeded and if there is an open-circuit fault detected with the external sense junctions. Status register 1 also indicates whether the ADC is converting. After POR, the normal state of the registers’ bits is zero (except bit 7 of status register 1), assuming no alert or overtemperature conditions are present. Bits 0 through 6 of status register 1 and bits 1 through 7 of status register 2 are cleared by any successful read of the status registers, unless the fault persists. The ALERT output follows the status flag bit. Both are cleared when successfully read, but if the condition still exists, they reassert at the end of the next conversion. The bits indicating OT1 and OT2 are cleared only on reading status even if the fault conditions still exist. Reading the status byte does not clear the OT1 and OT2 outputs. One way to eliminate the fault condition is for the measured temperature to drop below the temperature threshold minus the hysteresis value. Another way to eliminate the fault condition is by writing new values for the RWO2E, RWO2I, RWO1E, RWO1I, or HYST registers so that a fault condition is no longer present. When autoconverting, if the THIGH and TLOW limits are close together, it is possible for both high-temp and low-temp status bits to be set, depending on the amount of time between Status Read operations. In these circumstances, it is best not to rely on the status bits to indicate reversals in long-term temperature changes. Instead, use a current temperature reading to establish the trend direction. ______________________________________________________________________________________ 13 MAX6695/MAX6696 Table 6. Configuration Byte Functions MAX6695/MAX6696 Dual Remote/Local Temperature Sensors with SMBus Serial Interface Table 7. Status Register 1 Bit Assignments BIT NAME POR FUNCTION 7(MSB) BUSY 1 A/D is busy converting when 1. 6 LHIGH 0 When 1, internal high-temperature ALERT has tripped, cleared by POR or by reading this status register. If the fault condition still exists, this bit is set again after the next conversion. 5 LLOW 0 When 1, internal low-temperature ALERT has tripped, cleared by POR or by reading this status register. If the fault condition still exists, this bit is set again after the next conversion. 4 R1HIGH 0 A 1 indicates external junction 1 high-temperature ALERT has tripped, cleared by POR or by reading this status register. If the fault condition still exists, this bit is set again after the next conversion. 3 R1LOW 0 A 1 indicates external junction 1 low-temperature ALERT has tripped, cleared by POR or by reading this status register. If the fault condition still exists, this bit is set again after the next conversion. 2 1OPEN 0 A 1 indicates external diode 1 is open, cleared by POR or by reading this status register. If the fault condition still exists, this bit is set again after the next conversion. 1 R1OT1 0 A 1 indicates external junction 1 temperature exceeds the OT1 threshold, cleared by reading this register. 0 IOT1 0 A 1 indicates internal junction temperature exceeds the internal OT1 threshold, cleared by reading this register. Table 8. Status Register 2 Bit Assignments BIT NAME POR FUNCTION 7(MSB) IOT2 0 A 1 indicates internal junction temperature exceeds the internal OT2 threshold, cleared by reading this register. 6 R2OT2 0 A 1 indicates external junction temperature 2 exceeds the external OT2 threshold, cleared by reading this register. 5 R1OT2 0 A 1 indicates external junction temperature 1 exceeds the OT2 threshold, cleared by reading this register. 4 R2HIGH 0 A 1 indicates external junction 2 high-temperature ALERT has tripped; cleared by POR or readout of the status register. If the fault condition still exists, this bit is set again after the next conversion. 3 R2LOW 0 A 1 indicates external junction 2 low-temperature ALERT has tripped; cleared by POR or readout of the status register. If the fault condition still exists, this bit is set again after the next conversion. 2 2OPEN 0 A 1 indicates external diode 2 open; cleared by POR or readout of the status register. If the fault condition still exists, this bit is set again after the next conversion. 1 R2OT1 0 A 1 indicates external junction 2 temperature exceeds the OT1 threshold, cleared by reading this register. 0 RFU 0 Reserved. Reset (MAX6696 Only) Conversion Rate Byte The MAX6696’s registers are reset to their power-on values if RESET is driven high. When reset occurs, all registers go to their default values, and the SMBus address pins are sampled. The conversion-rate control register (Table 9) programs the time interval between conversions in free-running autonomous mode (RUN/STOP = 0). This variable rate control can be used to reduce the supply current in portable-equipment applications. The conversion rate 14 ______________________________________________________________________________________ Dual Remote/Local Temperature Sensors with SMBus Serial Interface CONVERSION RATE (Hz) REMOTE CHANNEL 1 CONVERSION PERIOD (s) REMOTE CHANNEL 2 AND LOCAL CONVERSION PERIOD (s) REMOTE CHANNEL 1 BIT 3 BIT 1 BIT0 HEX CONVERSION RATE (Hz) REMOTE CHANNEL 2 AND LOCAL 0 0 0 00h 0.0625 0.125 16 8 0 0 1 01h 0.125 0.25 8 4 0 1 0 02h 0.25 0.5 4 2 0 1 1 03h 0.5 1 2 1 1 0 0 04h 1 2 1 0.5 1 0 1 05h 2 4 0.5 0.25 1 1 0 06h 4 8 0.25 0.125 1 1 1 07h 4 8 0.25 0.125 Note: Extended resolution applies only for conversion rate control register values of 05h or less. byte’s POR state is 06h (4Hz). The MAX6695/MAX6696 use only the 3 LSBs of the control register. The 5 MSBs are don’t care and should be set to zero. The conversion rate tolerance is ±25% at any rate setting. Valid A/D conversion results for all channels are available one total conversion time after initiating a conversion, whether conversion is initiated through the RUN/STOP bit, hardware STBY pin, one-shot command, or initial power-up. Table 10. POR Slave Address Decoding (ADD0 and ADD1) ADD0 ADD1 ADDRESS GND GND 0011 000 GND High-Z 0011 001 0011 010 GND VCC High-Z GND 0101 001 Slave Addresses High-Z High-Z 0101 010 The MAX6695 has a fixed address of 0011 000. The MAX6696 device address can be set to any one of nine different values at power-up by pin strapping ADD0 and ADD1 so that more than one MAX6695/MAX6696 can reside on the same bus without address conflicts (Table 10). High-Z VCC 0101 011 VCC GND 1001 100 VCC High-Z 1001 101 VCC VCC 1001 110 The address pin states are checked at POR and RESET only, and the address data stays latched to reduce quiescent supply current due to the bias current needed for high-impedance state detection. The MAX6695/ MAX6696 also respond to the SMBus Alert Response slave address (see the Alert Response Address section). POR and UVLO To prevent unreliable power-supply conditions from corrupting the data in memory and causing erratic behavior, a POR voltage detector monitors VCC and clears the memory if VCC falls below 1.45V (typ; see Electrical Characteristics). When power is first applied and VCC rises above 2.0V (typ), the logic blocks begin operating, although reads and writes at V CC levels below 3.0V are not recommended. Power-Up Defaults • Interrupt latch is cleared. • Address select pin is sampled. • ADC begins autoconverting at a 4Hz rate for channel 2/local and 8Hz for channel 1. • Command register is set to 00h to facilitate quick internal Receive Byte queries. • THIGH and TLOW registers are set to default max and min limits, respectively. • Hysteresis is set to 10°C. ______________________________________________________________________________________ 15 MAX6695/MAX6696 Table 9. Conversion-Rate Control Register (POR = 0110) MAX6695/MAX6696 Dual Remote/Local Temperature Sensors with SMBus Serial Interface A tLOW B C tHIGH D E F G H I J K L 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 3. SMBus 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 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 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 tSU:STO tBUF J = ACKNOWLEDGE CLOCKED INTO SLAVE K = ACKNOWLEDGE CLOCK PULSE L = STOP CONDITION M = NEW START CONDITION Figure 4. SMBus Read Timing Diagram PC Board Layout Follow these guidelines to reduce the measurement error when measuring remote temperature: 1) Place the MAX6695/MAX6696 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. 16 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 +30°C error, even with good filtering. 3) Route the DXP and DXN traces in parallel and in close proximity to each other. Each parallel pair of traces (DXP1 and DXN or DXP2 and DXN) should go to a remote diode. Connect the two DXN traces at the MAX6695/MAX6696. Route these traces away from any higher voltage traces, such as +12VDC. ______________________________________________________________________________________ Dual Remote/Local Temperature Sensors with SMBus Serial Interface 10 mils 10 mils DXP 10 mils DXN MINIMUM 10 mils GND Figure 5. Recommended DXP-DXN PC Traces Leakage currents from PC board contamination must be dealt with carefully since a 20MΩ leakage path from DXP to ground causes about +1°C 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. Chip Information PROCESS: BiCMOS 6) When the power supply is noisy, add a resistor (up to 47Ω) in series with VCC (see Typical Operating Circuit). Typical Operating Circuits (continued) 0.1μF 47Ω +3.3V 10kΩ EACH CPU DXP1 VCC STBY SMBDATA SMBCLK DXN MAX6696 2N3906 DXP2 ADD0 ADD1 GND DATA CLOCK ALERT INTERRUPT TO μP OT1 TO CLOCK THROTTLING OT2 TO SYSTEM SHUTDOWN RESET ______________________________________________________________________________________ 17 MAX6695/MAX6696 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 distances up to 100ft in a noisy environment. At the device, connect the twisted pair to DXP and DXN and the shield to GND. Leave the shield unconnected at the remote sensor. For very long cable runs, the cable’s parasitic capacitance often provides noise filtering, so the 2200pF capacitor can often be removed or reduced in value. Cable resistance also affects remote-sensor accuracy. For every 1Ω of series resistance the error is approximately +1/2°C. GND Dual Remote/Local Temperature Sensors with SMBus Serial Interface MAX6695/MAX6696 Pin Configurations TOP VIEW N.C. 1 16 N.C. VCC 2 15 STBY 14 ADD0 DXP1 3 VCC 1 DXP1 2 DXN 3 DXP2 OT1 10 OT2 DXN 4 MAX6696 13 OT2 9 SMBDATA DXP2 5 12 SMBDATA 8 ALERT ADD1 6 11 ALERT 4 7 SMBCLK RESET 7 10 OT1 5 6 GND MAX6695 μMAX 9 GND 8 SMBCLK QSOP Package Information For the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. 18 PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 10 μMAX U10CN+1 21-0061 90-0330 16 QSOP E16+1 21-0055 90-0167 ______________________________________________________________________________________ Dual Remote/Local Temperature Sensors with SMBus Serial Interface REVISION NUMBER REVISION DATE 0 2/04 Initial release 1 5/04 Removed future status from MAX6696 in the Ordering Information table; updated the OT1 and OT2 Overtemperature Alarms section 1, 12 2 11/05 Updated the Features section, Ordering Information table, Electrical Characteristics table, and Effect of Ideality Factor section 1, 2, 6 3 4/11 DESCRIPTION PAGES CHANGED — Added lead(Pb)-free and tape-and-reel options to the Ordering Information table; added soldering information to the Absolute Maximum Ratings section; corrected the units for data setup time and data hold time from μs to ns in the Electrical Characteristics table; added the Package Information table 1, 2, 3, 18 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 19 © 2011 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc. MAX6695/MAX6696 Revision History