19-2920; Rev 3; 10/09 KIT ATION EVALU E L B AVAILA ±1°C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm The MAX6642 precise, two-channel digital temperature sensor accurately measures the temperature of its own die and a remote PN junction and reports the temperature data over a 2-wire serial interface. The remote PN junction is typically a substrate PNP transistor on the die of a CPU, ASIC, GPU, or FPGA. The remote PN junction can also be a discrete diode-connected smallsignal transistor. The 2-wire serial interface accepts standard system management bus (SMBus™), Write Byte, Read Byte, Send Byte, and Receive Byte commands to read the temperature data and to program the alarm thresholds. To enhance system reliability, the MAX6642 includes an SMBus timeout. The temperature data format is 10 bit with the least significant bit (LSB) corresponding to +0.25°C. The ALERT output asserts when the local or remote overtemperature thresholds are violated. A fault queue may be used to prevent the ALERT output from setting until two consecutive faults have been detected. Measurements can be done autonomously or in a single-shot mode. Remote accuracy is ±1°C maximum error between +60°C and +100°C. The MAX6642 operates from -40°C to +125°C, and measures remote temperatures between 0°C and +150°C. The MAX6642 is available in a 6-pin TDFN package with an exposed pad. Applications Features o Dual Channel: Measures Remote and Local Temperature o +0.25°C Resolution o High Accuracy ±1°C (max) (Remote) and ±2°C (Local) from +60°C to +100°C o Measures Remote Temperature Up to +150°C o Programmable Overtemperature Alarm Temperature Thresholds o SMBus/I2C-Compatible Interface o Tiny TDFN Package with Exposed Pad Ordering Information PART TEMP RANGE -40°C to +125°C 6 TDFN-EP* MAX6642ATT92-T -40°C to +125°C 6 TDFN-EP* MAX6642ATT94-T -40°C to +125°C 6 TDFN-EP* MAX6642ATT96-T -40°C to +125°C 6 TDFN-EP* MAX6642ATT98-T -40°C to +125°C 6 TDFN-EP* MAX6642ATT9A-T -40°C to +125°C 6 TDFN-EP* MAX6642ATT9C-T -40°C to +125°C 6 TDFN-EP* MAX6642ATT9E-T -40°C to +125°C 6 TDFN-EP* T = Tape and reel. *EP = Exposed pad. Pin Configuration and Functional Diagram appear at end of data sheet. Desktop Computers Notebook Computers Servers Thin Clients Test and Measurement Workstations Graphic Cards Typical Operating Circuit 3.3V 0.1μF Selector Guide PART PIN-PACKAGE MAX6642ATT90-T MEASURED TEMP RANGE 0°C to +150°C AFC MAX6642ATT92-T 0°C to +150°C AFD MAX6642ATT94-T 0°C to +150°C AFE MAX6642ATT96-T 0°C to +150°C AFF MAX6642ATT98-T 0°C to +150°C AEW MAX6642ATT9A-T 0°C to +150°C AFG MAX6642ATT9C-T 0°C to +150°C AFH MAX6642ATT9E-T 0°C to +150°C SMBus is a trademark of Intel Corp. AFI 10kΩ EACH VCC TOP MARK MAX6642ATT90-T 47Ω 2200pF DXP MAX6642 SDA SCLK ALERT μP DATA CLOCK INTERRUPT TO μP GND ________________________________________________________________ Maxim Integrated Products 1 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. MAX6642 General Description MAX6642 ±1°C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm ABSOLUTE MAXIMUM RATINGS All Voltages Referenced to GND VCC ...........................................................................-0.3V to +6V DXP.............................................................-0.3V to (VCC + 0.3V) SCLK, SDA, ALERT ..................................................-0.3V to +6V SDA, ALERT Current ...........................................-1mA to +50mA Continuous Power Dissipation (TA = +70°C) 6-Pin TDFN (derate 24.4mW/°C above +70°C) .........1951mW ESD Protection (all pins, Human Body Model) ................±2000V Junction Temperature ......................................................+150°C Operating Temperature Range .........................-40°C to +125°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°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 +5.5V, TA = -40°C to +125°C, unless otherwise specified. Typical values are at VCC = +3.3V and TA = +25°C.) (Note 1) PARAMETER Supply Voltage SYMBOL CONDITIONS VCC MIN Temperature Resolution Remote Temperature Error VCC = 3.3V Local Temperature Error VCC = 3.3V 5.5 10 Bits +1.0 TRJ = 0°C to +125°C -3.0 +3.0 TRJ = +125°C to +150°C -3.5 +3.5 TA = +60°C to +100°C -2.0 +2.0 TA = 0°C to +125°C -3.0 +3.0 Falling edge of VCC disables ADC 2.4 2.7 VCC falling edge 1.5 POR Threshold Hysteresis 2.0 2.95 SMBus static Operating Current During conversion Average Operating Current 2.4 tCONV Conversion Rate fCONV IRJ V V mV 3 10 µA 0.5 1.0 mA 143 ms 260 Conversion Time °C mV 90 Standby Supply Current °C °C/V 90 Power-On-Reset (POR) Threshold V °C ±0.2 UVLO UNITS 0.25 -1.0 Undervoltage Lockout Hysteresis Remote-Diode Source Current MAX TRJ = +60°C to +100°C, TA = +25°C to +85°C Supply Sensitivity of Temperature Error Undervoltage Lockout Threshold TYP 3.0 µA From stop bit to conversion completion 106 125 High level 80 100 120 Low level 8 10 12 VOL = 0.4V 1 VOL = 0.6V 4 8 Hz µA ALERT Output-Low Sink Current Output-High Leakage Current 2 VOH = VCC _______________________________________________________________________________________ mA 1 µA ±1°C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm (VCC = +3.0V to +5.5V, TA = -40°C to +125°C, unless otherwise specified. Typical values are at VCC = +3.3V and TA = +25°C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 0.8 V +1 µA SMBus-COMPATIBLE INTERFACE (SCLK and SDA) Logic Input Low Voltage VIL Logic Input High Voltage VIH Input Leakage Current ILEAK Output Low Sink Current IOL Input Capacitance CIN VCC = 3.0V 2.2 VIN = GND or 5.5V -1 VOL = 0.6V 6 V mA 5 pF SMBus TIMING (Note 2) Serial Clock Frequency fSCLK Bus Free Time Between STOP and START Condition tBUF (Note 3) START Condition Setup Time 100 kHz 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 SDA to 90% of SCLK 4 µs STOP Condition Setup Time tSU:STO 90% of SCLK to 90% of SDA 4 µs 4.7 µs 4 µs Clock Low Period Clock High Period Data Setup Time tLOW 10% to 10% tHIGH 90% to 90% tHD:DAT Receive SCLK/SDA Rise Time tF Pulse Width of Spike Suppressed tSP Note 1: Note 2: Note 3: Note 4: 250 µs tR Receive SCLK/SDA Fall Time SMBus Timeout (Note 4) tTIMEOUT 1 0 SDA low period for interface reset 20 28 µs 300 ns 50 ns 40 ms All parameters tested at TA = +25°C. Specifications over temperature are guaranteed by design. Timing specifications guaranteed by design. The serial interface resets when SCLK is low for more than tTIMEOUT. A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SCLK’s falling edge. _______________________________________________________________________________________ 3 MAX6642 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VCC = 3.3V, TA = +25°C, unless otherwise noted.) STANDBY SUPPLY CURRENT vs. CLOCK FREQUENCY 4.0 3.5 3.0 2.5 2.0 1 0.1 1 10 0 100 100 125 TEMPERATURE ERROR vs. POWER-SUPPLY NOISE FREQUENCY TEMPERATURE ERROR (°C) 1.5 -1 -2 25 50 75 100 REMOTE ERROR 1.0 LOCAL ERROR 0.5 0 -0.5 -1.0 -3 VIN = 100mVP-P SQUARE WAVE APPLIED TO VCC WITH NO BYPASS CAPACITOR -1.5 0.0001 0.001 125 MAX6642 toc04 2.0 MAX 6642 toc03 0 0.01 0.1 1 10 TEMPERATURE (°C) FREQUENCY (kHz) TEMPERATURE ERROR vs. DXP NOISE FREQUENCY TEMPERATURE ERROR vs. DXP-GND CAPACITANCE 70 REMOTE ERROR 50 40 LOCAL ERROR 20 100 MAX6642 toc06 1.0 TEMPERATURE ERROR (°C) VIN = AC-COUPLED TO DXP VIN = 100mVP-P SQUARE WAVE 60 2.0 MAX6642 toc05 100 0 -1.0 -2.0 -3.0 -4.0 -5.0 10 0 0.001 75 LOCAL TEMPERATURE ERROR vs. DIE TEMPERATURE 1 30 50 TEMPERATURE (°C) 2 0 25 CLOCK FREQUENCY (kHz) 3 TEMPERATURE ERROR (°C) -2 2N3906 0.01 -6.0 0.01 0.1 1 FREQUENCY (kHz) 4 -1 -4 1.0 80 0 -3 1.5 90 MAX6642 toc02 2 TEMPERATURE ERROR (°C) 4.5 SUPPLY CURRENT (μA) REMOTE TEMPERATURE ERROR vs. REMOTE-DIODE TEMPERATURE MAX6642 toc01 5.0 TEMPERATURE ERROR (°C) MAX6642 ±1°C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm 10 100 0.1 1 10 DXP-GND CAPACITANCE (nF) _______________________________________________________________________________________ 100 ±1°C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm PIN NAME FUNCTION Supply Voltage Input, +3V to +5.5V. Bypass VCC to GND with a 0.1µF capacitor. A 47Ω series resistor is recommended but not required for additional noise filtering. 1 VCC 2 GND Ground 3 DXP Combined Remote-Diode Current Source and ADC Input for Remote-Diode Channel. Place a 2200pF capacitor between DXP and GND for noise filtering. 4 SCLK SMBus Serial-Clock Input. May be pulled up to +5.5V regardless of VCC. 5 SDA SMBus Serial-Data Input/Output, Open Drain. May be pulled up to +5.5V regardless of VCC. 6 ALERT — EP SMBus Alert (Interrupt) Output, Open Drain. ALERT asserts when temperature exceeds user-set limits. See the ALERT Interrupts section. Exposed Pad. Internally connected to GND. Connect to a PCB ground pad for optimal performance. Not intended as an electrical connection point. Detailed Description The MAX6642 is a temperature sensor for local and remote temperature-monitoring applications. Communication with the MAX6642 occurs through the SMBus-compatible serial interface and dedicated alert pins. ALERT asserts if the measured local or remote temperature is greater than the software-programmed ALERT limit. The MAX6642 converts temperatures to digital data either at a programmed rate of eight conversions per second or in single conversions. Temperature data is represented by 8 data bits (at addresses 00h and 01h), with the LSB equal to +1°C and the MSB equal to +128°C. Two additional bits of remote temperature data are available in the “extended” register at address 10h and 11h (Table 2) providing resolution of +0.25°C. ADC and Multiplexer The averaging ADC integrates over a 60ms period (each channel, typ), with excellent noise rejection. The multiplexer automatically steers bias currents through the remote and local diodes. The ADC and associated circuitry measure each diode’s forward voltage and compute the temperature based on this voltage. Both channels are automatically converted once the conversion process has started, either in free-running or single-shot mode. If one of the two channels is not used, the device still performs both measurements, and the user can ignore the results of the unused channel. If the remote-diode channel is unused, connect DXP to GND rather than leaving DXP open. The conversion time per channel (remote and internal) is 125ms. If both channels are being used, then each channel is converted four times per second. If the external conversion-only option is selected, then the remote temperature is measured eight times per second. The results of the previous conversion are always available, even if the ADC is busy. Low-Power Standby Mode Standby mode reduces the supply current to less than 10µA by disabling the ADC and timing circuitry. Enter standby mode by setting the RUN bit to 1 in the configuration byte register (Table 4). All data is retained in memory, and the SMBus interface is active and listening for SMBus commands. Standby mode is not a shutdown mode. With activity on the SMBus, the device draws more supply current (see the Typical Operating Characteristics). In standby mode, the MAX6642 can be forced to perform ADC conversions through the one-shot command, regardless of the RUN bit status. If a 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 a temperature register. The previous data is not changed and remains available. Supply-current drain during the 125ms conversion period is 500µA (typ). In standby mode, supply current drops to 3µA (typ). SMBus Digital Interface From a software perspective, the MAX6642 appears as a set of byte-wide 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 MAX6642 employs four standard SMBus protocols: Write Byte, Read Byte, Send Byte, and Receive Byte. (Figures 1, 2, and 3). The shorter Receive Byte protocol allows quicker transfers, provided that the correct data _______________________________________________________________________________________ 5 MAX6642 Pin Description MAX6642 ±1°C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm WRITE BYTE FORMAT S ADDRESS WR ACK COMMAND 7 BITS ACK DATA 8 BITS ACK P 8 BITS SLAVE ADDRESS: EQUIVALENT TO CHIP-SELECT LINE OF A 3-WIRE INTERFACE 1 DATA BYTE: DATA GOES INTO THE REGISTER SET BY THE COMMAND BYTE (TO SET THRESHOLDS, CONFIGURATION MASKS, AND SAMPLING RATE) READ BYTE FORMAT S ADDRESS WR ACK COMMAND 7 BITS ACK S SLAVE ADDRESS: EQUIVALENT TO CHIP SELECT LINE ADDRESS RD ACK DATA 7 BITS COMMAND BYTE: SELECTS WHICH REGISTER YOU ARE REDING FROM P DATA BYTE: READS FROM THE REGISTER SET BY THE COMMAND BYTE RECEIVE BYTE FORMAT WR ACK COMMAND 7 BITS ACK P S ADDRESS 8 BITS RD ACK DATA 7 BITS /// P 8 BITS COMMAND BYTE: SENDS COMMAND WITH NO DATA, USUALLY USED FOR ONE-SHOT COMMAND S = START CONDITION P = STOP CONDITION /// 8 BITS SLAVE ADDRESS: REPEATED DUE TO CHANGE IN DATAFLOW DIRECTION SEND BYTE FORMAT S ADDRESS 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 SHADED = SLAVE TRANSMISSION /// = NOT ACKNOWLEDGED Figure 1. SMBus Protocols A B tLOW C D E F G tHIGH H I J K L M SMBCLK SMBDATA tSU:STA tHD:STA A = START CONDITION B = MSB OF ADDRESS CLOCKED INTO SLAVE C = LSB OF ADDRESS CLOCKED INTO SLAVE D = R/W BIT CLOCKED INTO SLAVE tSU:STO tSU:DAT E = SLAVE PULLS SMBDATA LINE LOW F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO SLAVE H = LSB OF DATA CLOCKED INTO SLAVE I = SLAVE PULLS DATA LINE LOW J = ACKNOWLEDGE CLOCKED INTO MASTER K = ACKNOWLEDGE CLOCK PULSE L = STOP CONDITION M = NEW START CONDITION Figure 2. SMBus Write Timing Diagram 6 _______________________________________________________________________________________ tBUF ±1°C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm register was previously selected by a Write Byte instruction. Use caution when using the shorter protocols in multimaster systems, as a second master could overwrite the command byte without informing the first master. Read temperature data from the read internal temperature (00h) and read external temperature (01h) registers. The temperature data format for these registers is 8 bits for each channel, with the LSB representing +1°C (Table 1). Read the additional bits from the read extended temperature byte register (10h, 11h), which extends the data to 10 bits and the resolution to +0.25°C per LSB (Table 2). When a conversion is complete, the main temperature register and the extended temperature register are updated. Two registers store ALERT threshold values—one each for the local and remote channels. If either measured temperature equals or exceeds the corresponding ALERT threshold value, the ALERT interrupt asserts unless the ALERT bit is masked. The power-on-reset (POR) state of the local ALERT THIGH register is +70°C (0100 0110). The POR state of the remote ALERT THIGH register is +120°C (0111 1000). tHIGH C D E 127.00 0 111 1111 126.00 0 111 1110 25 0 001 1001 0.00 0 000 0000 <0.00 0 000 0000 Diode fault (short or open) 1 111 1111 FRACTIONAL TEMP (°C) DIGITAL OUTPUT 0.000 00XX XXXX 0.250 01XX XXXX 0.500 10XX XXXX 0.750 11XX XXXX ALERT Interrupts The ALERT interrupt occurs when the internal or external temperature reading exceeds a high temperature limit (user programmed). The ALERT interrupt output signal is latched and can be cleared only by reading the status register after the fault condition no longer exists or by successfully responding to the alert response address. If A continuity fault detector at DXP detects an open circuit on DXP, or a DXP short to VCC or GND. If an open or short circuit exists, the external temperature register is loaded with 1111 1111 and status bit 2 (OPEN) of the status byte is set to 1. Immediately after POR, the status register indicates that no fault is present. If a fault is B 1 000 0010 present upon power-up, the fault is not indicated until the end of the first conversion. Diode faults do not set the ALERT output. Diode Fault Detection tLOW DIGITAL OUTPUT 130.00 Table 2. Extended Resolution Temperature Register (Low Byte) Data Format Alarm Threshold Registers A TEMP (°C) MAX6642 Table 1. Main Temperature Register (High Byte) Data Format F G H I J K SMBCLK SMBDATA tSU:STA tHD:STA A = START CONDITION B = MSB OF ADDRESS CLOCKED INTO SLAVE C = LSB OF ADDRESS CLOCKED INTO SLAVE D = R/W BIT CLOCKED INTO SLAVE E = SLAVE PULLS SMBDATA LINE LOW tSU:DAT tHD:DAT F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO MASTER H = LSB OF DATA CLOCKED INTO MASTER tSU:STO tBUF I = ACKNOWLEDGE CLOCK PULSE J = STOP CONDITION K = NEW START CONDITION Figure 3. SMBus Read Timing Diagram _______________________________________________________________________________________ 7 MAX6642 ±1°C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm Table 3. Command-Byte Assignments ADDRESS POR STATE FUNCTION 00h 00h (0000 0000) Read local temperature 01h 00h (0000 0000) Read remote temperature 02h N/A Read status byte 03h 10h (0001 0000) Read configuration byte 05h 46h (0100 0110) +70°C Read local high limit 07h 78h (0111 1000) +120°C Read remote high limit 09h N/A Write configuration byte 0Bh N/A Write local high limit 0Dh N/A Write remote high limit 0Fh N/A Single shot 10h 0000 0000 Read remote extended temperature 11h 0000 0000 Read internal extended temperature FEh 4Dh (0100 1101) Read manufacturer ID the ALERT is cleared by responding to the alert response address and the temperature fault condition still exists, ALERT is reasserted after the next temperature-monitoring cycle. To clear ALERT while the temperature is above the trip threshold, write a new high limit that is higher than the current temperature. The ALERT output is open drain, allowing multiple devices to share a common interrupt line. Alert Response Address The SMBus alert response interrupt pointer provides quick fault identification for simple slave devices like temperature sensors. Upon receiving an ALERT interrupt signal, the host master can broadcast a Receive Byte transmission to the alert response slave address (0001 100). Following such a broadcast, 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 arbitra- Table 4. Configuration-Byte Bit Assignments BIT NAME POR STATE FUNCTION 7 (MSB) MASK1 0 A 1 masks off (disables) the ALERT interrupts. 6 STOP/RUN 0 A 1 puts the MAX6642 into standby mode. 5 External only 0 A 1 disables local temperature measurements so that only remote temperature is measured. The measurement rate becomes 8Hz. 4 Fault queue 1 0: ALERT is set by a single fault. 1: Two consecutive faults are required to set ALERT. 3 to 0 — 0000 Reserved. Table 5. Status-Byte Bit Assignments 8 BIT NAME POR STATE FUNCTION 7 (MSB) BUSY 0 A 1 indicates the MAX6642 is busy converting. A 1 indicates an internal high-temperature fault. Clear LHIGH with a POR or by reading the status byte. 6 LHIGH 0 5 — 0 Reserved. A 1 indicates an external high-temperature fault. Clear RHIGH with a POR or by reading the status byte. 4 RHIGH 0 3 — 0 Reserved. 2 OPEN 0 A 1 indicates a diode open condition. Clear OPEN with a POR or by reading the status byte when the condition no longer exists. 1 to 0 — 0 Reserved. _______________________________________________________________________________________ ±1°C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm Command Byte Functions The 8-bit command byte register (Table 3) is the master index that points to the various other registers within the MAX6642. 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 local temperature data. Status Byte Functions The status byte register (Table 5) indicates which (if any) temperature thresholds have been exceeded. This byte also indicates whether the ADC is converting and whether there is an open-circuit fault detected on the external sense junction. After POR, the normal state of all flag bits is zero, assuming no alarm conditions are present. The status byte is cleared by any successful read of the status byte after the overtemperature fault condition no longer exists. Slave Addresses The MAX6642 has eight fixed addresses available. These are shown in Table 6. The MAX6642 also responds to the SMBus alert response slave address (see the Alert Response Address section). Single-Shot The single-shot command immediately forces a new conversion cycle to begin. If the single-shot command is received while the MAX6642 is in standby mode (RUN bit = 1), a new conversion begins, after which the device returns to standby mode. If a single-shot conversion is in progress when a single-shot command is received, the command is ignored. If a single-shot command is received in autonomous mode (RUN bit = 0), the command is ignored. Configuration Byte Functions The configuration byte register (Table 4) is a read-write register with several functions. Bit 7 is used to mask (disable) interrupts. Bit 6 puts the MAX6642 into standby mode (STOP) or autonomous (RUN) mode. Bit 5 disables local temperature conversions for faster (8Hz) remote temperature monitoring. Bit 4 prevents setting the ALERT output until two consecutive measurements result in fault conditions. POR and UVLO To prevent ambiguous 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 2.1 (typ). When power is first applied and VCC rises above 2.1 (typ), the logic blocks begin operating, although reads and writes at VCC levels below 3V are not recommended. A second VCC comparator, the ADC undervoltage lockout (UVLO) comparator prevents the ADC from converting until there is sufficient headroom (VCC = +2.7V typ). Power-Up Defaults Power-up defaults include: • ALERT output is cleared. • ADC begins autoconverting at a 4Hz rate. • Command byte is set to 00h to facilitate quick local Receive Byte queries. • Local (internal) THIGH limit set to +70°C. • Remote (external) THIGH limit set to +120°C. Applications Information Table 6. Slave Address Remote-Diode Selection PART NO. SUFFIX ADDRESS MAX6642ATT90 1001 000 MAX6642ATT92 1001 001 MAX6642ATT94 1001 010 MAX6642ATT96 1001 011 MAX6642ATT98 1001 100 MAX6642ATT9A 1001 101 MAX6642ATT9C 1001 110 MAX6642ATT9E 1001 111 The MAX6642 can directly measure the die temperature of CPUs and other ICs that have on-board temperaturesensing diodes (see the Typical Operating Circuit) or they can measure the temperature of a discrete diodeconnected transistor. Effect of Ideality Factor The accuracy of the remote temperature measurements depends on the ideality factor (n) of the remote “diode” (actually a transistor). The MAX6642 is optimized for n = 1.008, which is the typical value for the Intel Pentium _______________________________________________________________________________________ 9 MAX6642 tion rules apply, and the device with the lower address code wins. The losing device does not generate an acknowledge 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. If the condition still exists, the device reasserts the ALERT interrupt at the end of the next conversion. MAX6642 ±1°C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm III. A thermal diode on the substrate of an IC is normally a PNP with its collector grounded. Connect the anode (emitter) to DXP and the cathode to GND of the MAX6642. If a sense transistor with an ideality factor other than 1.008 is used, the output data is different from the data obtained with the optimum ideality factor. Fortunately, the difference is predictable. Assume a remote-diode sensor designed for a nominal ideality factor nNOMINAL is used to measure the temperature of a diode with a different ideality factor n1. The measured temperature TM can be corrected using: ⎛ ⎞ n1 TM = TACTUAL ⎜ ⎟ ⎝ nNOMINAL ⎠ where temperature is measured in Kelvin and nNOMIMAL for the MAX6642 is 1.008. As an example, assume you want to use the MAX6642 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 ⎞ TACTUAL = TM ⎜ NOMINAL ⎟ = TM ⎜ ⎟= ⎝ 1.002 ⎠ n ⎝ ⎠ 1 Table 7. Remote-Sensor Transistor Manufacturers MANUFACTURER MODEL NO. Central Semiconductor (USA) CMPT3906 Rohm Semiconductor (USA) SST3906 Samsung (Korea) KST3906-TF Siemens (Germany) SMBT3906 Zetex (England) FMMT3906CT-ND Note: Discrete transistors must be diode connected (base shorted to collector). 3Ω × 0.453 °C = +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 TM (1.00599) For a real temperature of +85°C (358.15K), the measured temperature is +82.91°C (356.02K), an error of -2.13°C. Effect of Series Resistance Series resistance in a sense diode contributes additional errors. For nominal diode currents of 10µA and 100µA, the change in the measured voltage due to series resistance is: ΔVM = RS (100µA - 10µA) = 90µA RS Since +1°C corresponds to 198.6µV, series resistance contributes a temperature offset of: μV Ω = 0.453 °C μV Ω 198.6 °C 90 Assume that the diode being measured has a series resistance of 3Ω. The series resistance contributes an offset of: 10 for a diode temperature of +85°C. 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, connect its collector and base together. Table 7 lists examples of discrete transistors that are appropriate for use with the MAX6642. 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 ______________________________________________________________________________________ ±1°C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm ADC Noise Filtering The integrating ADC used has good noise rejection for low-frequency signals such as 60Hz/120Hz power-supply hum. In noisy environments, high-frequency noise reduction is needed for high-accuracy remote measurements. The noise can be reduced with careful PCB layout and proper external noise filtering. High-frequency EMI is best filtered at DXP with an external 2200pF capacitor. Larger capacitor values can be used for added filtering, but do not exceed 3300pF because excessive capacitance can introduce errors due to the rise time of the switched current source. Nearly all noise sources tested cause the temperature conversion results to be higher than the actual temperature, typically by +1°C to +10°C, depending on the frequency and amplitude (see the Typical Operating Characteristics). PCB Layout Follow these guidelines to reduce the measurement error of the temperature sensors: 1) Connect the thermal-sense diode to the MAX6642 using two traces—one between DXP and the anode, the other between the MAX6642’s GND and the cathode. Do not connect the cathode to GND at the sense diode. 2) Place the MAX6642 as close as is practical to the remote thermal 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 ISA/PCI buses. 3) Do not route the thermal diode lines next to the deflection coils of a CRT. Also, do not route the traces across fast digital signals, which can easily introduce a 30°C error, even with good filtering. 4) Route the thermal diode traces in parallel and in close proximity to each other, away from any higher voltage traces, such as +12VDC. Leakage currents from PCB 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 trace (Figure 4). 5) Route through as few vias and crossunders as possible to minimize copper/solder thermocouple effects. 6) When introducing a thermocouple, make sure that both the thermal diode paths have matching thermocouples. A copper-solder thermocouple exhibits 3µV/°C, and it takes about 200µV of voltage error at DXP to cause a +1°C measurement error. Adding a few thermocouples causes a negligible error. 7) Use wide traces. Narrow traces are more inductive and tend to pick up radiated noise. The 10-mil widths and spacing recommended in Figure 4 are not absolutely necessary, as they offer only a minor improvement in leakage and noise over narrow traces. Use wider traces when practical. 8) Add a 47Ω resistor in series with VCC for best noise filtering (see the Typical Operating Circuit). 9) Copper cannot be used as an EMI shield; only ferrous materials such as steel work well. Placing a copper ground plane between the DXP-DXN traces and traces carrying high-frequency noise signals does not help reduce EMI. 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 GND and the shield to GND. Leave the shield unconnected at the remote diode. 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. GND 10 mils 10 mils THERMAL DIODE ANODE/DXP MINIMUM 10 mils THERMAL DIODE CATHODE/GND 10 mils GND Figure 4. Recommended DXP PC Traces ______________________________________________________________________________________ 11 MAX6642 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. MAX6642 ±1°C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm Cable resistance also affects remote-sensor accuracy. For every 1Ω of series resistance, the error is approximately 1/2°C. Thermal Mass and Self-Heating When sensing local temperature, this device is intended to measure the temperature of the PCB to which it is soldered. The leads provide a good thermal path between the PCB traces and the die. Thermal conductivity between the die and the ambient air is poor by comparison, making air temperature measurements impractical. Because the thermal mass of the PCB is far greater than that of the MAX6642, the device follows temperature changes on the PCB with little or no perceivable delay. When measuring 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 sensors, smaller packages, such as SOT23s, yield the best thermal response times. 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. 12 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, with V CC = +5.0V, at an 8Hz conversion rate and with ALERT sinking 1mA, the typical power dissipation is: 5.0V x 450µA + 0.4V x 1mA = 2.65mW øJ-A for the 6-pin TDFN package is about +41°C/W, so assuming no copper PCB heat sinking, the resulting temperature rise is: ΔT = 2.65mW x 41°C/W = +0.11°C Even under nearly worst-case conditions, it is difficult to introduce a significant self-heating error. ______________________________________________________________________________________ ±1°C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm VCC 2 MUX REMOTE DXP CONTROL LOGIC ADC LOCAL DIODE FAULT SMBus 8 ALERT S 8 Q R SDA READ SCLK WRITE REGISTER BANK COMMAND BYTE 7 REMOTE TEMPERATURE MAX6642 LOCAL TEMPERATURE ALERT THRESHOLD ADDRESS DECODER ALERT RESPONSE ADDRESS Pin Configuration Chip Information PROCESS: BiCMOS TOP VIEW MAX6642 Package Information VCC 1 6 ALERT GND 2 5 SDA DXP 3 4 SCLK EP* For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE PACKAGE CODE DOCUMENT NO. 6 TDFN-EP T633-2 21-0137 TDFN-EP *EXPOSED PAD CONNECTED TO GND. ______________________________________________________________________________________ 13 MAX6642 Functional Diagram MAX6642 ±1°C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm Revision History PAGES CHANGED REVISION NUMBER REVISION DATE 0 8/03 Initial release 1 10/08 Added missing EP description to Ordering Information and Pin Description, removed the transistor count on page 12, and corrected some minor style issues 2 7/09 Corrected errors in Figures 2 and 3 6, 7 3 10/09 Corrected error in Package Information table 13 DESCRIPTION — 1, 5, 9, 10, 12 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. 14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.