19-2540; Rev 3; 5/07 +145°C Precision SMBus-Compatible Remote/ Local Sensors with Overtemperature Alarms Features The MAX6646/MAX6647/MAX6649 are precise, twochannel digital temperature sensors. The devices accurately measure the temperature of their own die and a remote PN junction, and report the temperature in digital form using a 2-wire serial interface. The remote PN junction is typically the emitter-base junction of a commoncollector PNP on a CPU, FPGA, or ASIC. ♦ Dual Channel: Measures Remote and Local Temperature The 2-wire serial interface accepts standard system management bus (SMBusTM) 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 MAX6646/MAX6647/MAX6649 include an SMBus timeout. A fault queue prevents the ALERT and OVERT outputs from setting until a fault has been detected one, two, or three consecutive times (programmable). The MAX6646/MAX6647/MAX6649 provide two system alarms: ALERT and OVERT. ALERT asserts when any of four temperature conditions are violated: local overtemperature, remote overtemperature, local undertemperature, or remote undertemperature. OVERT asserts when the temperature rises above the value in either of the two OVERT limit registers. The OVERT output can be used to activate a cooling fan, or to trigger a system shutdown. Measurements can be done autonomously, at the programmed conversion rate, or in a single-shot mode. The adjustable conversion rate allows optimizing supply current and temperature update rate to match system needs. Remote accuracy is ±1°C maximum error between +60°C and +145°C with no calibration needed. The MAX6646/ MAX6647/MAX6649 operate from -55°C to +125°C, and measure temperatures between 0°C and +145°C. The MAX6646/MAX6647/MAX6649 are available in an 8-pin µMAX® package. ♦ Measures High-Ideality Thermal Diodes Up to +170°C (Apparent) +145°C (Real) ♦ 0.125°C Resolution ♦ High Accuracy ±1°C (max) from +60°C to +145°C (Remote), and ±2°C (max) from +60°C to +100°C (Local) ♦ Two Alarm Outputs: ALERT and OVERT ♦ Programmable Under/Overtemperature Alarm Temperature Thresholds ♦ Programmable Conversion Rate ♦ SMBus-Compatible Interface ♦ SMBus Timeout Ordering Information PART TEMP RANGE PINMEASURED PACKAGE TEMP RANGE MAX6646MUA -55°C to +125°C 8 µMAX 0°C to +145°C MAX6647MUA -55°C to +125°C 8 µMAX 0°C to +145°C MAX6649MUA -55°C to +125°C 8 µMAX 0°C to +145°C Typical Operating Circuit 3.3V Applications 0.1μF 200Ω Graphics Processors VCC Desktop Computers Notebook Computers DXP MAX6646 SDA MAX6647 MAX6649 SCLK DXN ALERT INTERRUPT TO μP OVERT TO FAN DRIVER OR SYSTEM SHUTDOWN Servers Thin Clients Workstations Test and Measurement 2200pF μP 10kΩ EACH GND DATA CLOCK Multichip Modules SMBus is a trademark of Intel Corp. µMAX is a registered trademark of Maxim Integrated Products, Inc. Selector Guide, Pin Configurations, and Functional Diagram appear at end of data sheet. ________________________________________________________________ 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 MAX6646/MAX6647/MAX6649 General Description MAX6646/MAX6647/MAX6649 +145°C Precision SMBus-Compatible Remote/ Local Sensors with Overtemperature Alarms ABSOLUTE MAXIMUM RATINGS ESD Protection (all pins, Human Body Model) ................±2000V Junction Temperature ......................................................+150°C Operating Temperature Range .........................-55°C to +125°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C All Voltages Referenced to GND VCC ...........................................................................-0.3V to +6V DXP.............................................................-0.3V to (VCC + 0.3V) DXN .......................................................................-0.3V to +0.8V SCLK, SDA, ALERT, OVERT.....................................-0.3V to +6V SDA, ALERT, OVERT Current .............................-1mA to +50mA DXN Current .......................................................................±1mA Continuous Power Dissipation (TA = +70°C) 8-Pin µMAX (derate 4.8mW/°C above +70°C) ..........387.8mW 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 = -55°C to +125°C, unless otherwise specified. Typical values are at VCC = 3.3V and TA = +100°C.) (Note 1) PARAMETER Supply Voltage SYMBOL CONDITIONS VCC MIN Local Temperature Error °C Bits -1.0 +1.0 VCC = 3.3V, TA = +60°C to +100°C, TRJ = +25°C to +145°C -1.6 +1.6 VCC = 3.3V, TA = +0°C to +100°C, TRJ = +0°C to +145°C -3.2 +3.2 TA = +60°C to +100°C -2.0 +2.0 TA = 0°C to +125°C -3.0 +3.0 VCC = 3.3V ±0.2 UVLO Falling edge of VCC disables ADC 2.4 UVLO Hysteresis 2.7 VCC falling edge POR Threshold Hysteresis Standby Supply Current SMBus static Operating Current During conversion Average Operating Current 2.95 tCONV V 90 mV 3 0.08 mA 250 400 125 Standby mode IRJ µA 2 conversions per second -25 DXP and DXN Leakage Current 12 80 95 V 2.0 40 From stop bit to conversion completion °C mV 0.25 conversions per second Conversion Time Error °C °C/V 90 Power-On-Reset (POR) Threshold 2 V VCC = 3.3V, TA = +100°C, TRJ = +60°C to +145°C Supply Sensitivity of Temperature Error Remote-Diode Source Current UNITS 5.5 11 Remote Temperature Error Conversion Time MAX 0.125 Temperature Resolution Undervoltage Lockout (UVLO) Threshold TYP 3.0 156 ms +25 % 100 nA High level 80 100 120 Low level 8 10 12 _______________________________________________________________________________________ µA µA +145°C Precision SMBus-Compatible Remote/ Local Sensors with Overtemperature Alarms (VCC = 3.0V to 5.5V, TA = -55°C to +125°C, unless otherwise specified. Typical values are at VCC = 3.3V and TA = +100°C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS ALERT, OVERT Output Low Voltage Output High Leakage Current ISINK = 1mA 0.4 ISINK = 4mA 0.6 VOH = 5.5V 1 µA 0.8 V V SMBus-COMPATIBLE INTERFACE (SCLK AND SDA) Logic Input Low Voltage Logic Input High Voltage VIL VIH VCC = 3.0V 2.2 VCC = 5.5V 2.6 Input Leakage Current ILEAK VIN = GND or VCC -1 Output Low-Sink Current ISINK VOL = 0.6V 6 Input Capacitance CIN V +1 µA mA 5 pF SMBus-COMPATIBLE 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 Clock Low Period tLOW 10% to 10% 4.7 µs Clock High Period tHIGH 90% to 90% 4 µs Data Setup Time tHD:DAT (Note 4) 250 µs Receive SCLK/SDA Rise Time tR 1 µs Receive SCLK/SDA Fall Time tF 300 ns Pulse Width of Spike Suppressed SMBus Timeout Note 1: Note 2: Note 3: Note 4: tSP tTIMEOUT 0 SDA low period for interface reset 25 37 50 ns 55 ms All parameters tested at a single temperature. 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 MAX6646/MAX6647/MAX6649 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VCC = 3.3V, TA = +25°C, unless otherwise noted.) 3.5 3.0 1.5 TEMPERATURE ERROR (°C) 4.0 2.0 MAX6649 toc02 OPERATING SUPPLY CURRENT (μA) 4.5 REMOTE TEMPERATURE ERROR vs. REMOTE-DIODE TEMPERATURE 400 MAX6649 toc01 300 200 100 1.0 0.5 0 -0.5 -1.0 TA = +85°C FAIRCHILD 2N3906 -1.5 2.5 0 3.5 4.0 4.5 -2.0 5.5 5.0 0.63 0.13 0.25 0.50 1.00 2.00 4.00 75 100 125 TEMPERATURE (°C) LOCAL TEMPERATURE ERROR vs. DIE TEMPERATURE TEMPERATURE ERROR vs. POWER-SUPPLY NOISE FREQUENCY LOCAL TEMPERATURE ERROR vs. COMMON-MODE NOISE FREQUENCY 5 MAX6649 toc04 LOCAL ERROR 0 -0.5 -1.0 -1.5 3 REMOTE ERROR 2 1 0 VCC = SQUARE WAVE APPLIED TO VCC WITH NO BYPASS CAPACITOR -1 -2.0 75 125 100 6 5 REMOTE ERROR 4 3 2 LOCAL ERROR 1 0 -2 0.1 1 TEMPERATURE (°C) 10 100 1k 10k 100k 1 10 FREQUENCY (Hz) TEMPERATURE ERROR vs. DIFFERENTIAL-MODE NOISE FREQUENCY 1 0 TEMPERATURE ERROR (°C) 1.5 1.0 0.5 0 -0.5 100 -1 -2 -3 -4 -1.0 1 10 100 1k FREQUENCY (Hz) 10k 100k -5 0.100 1k FREQUENCY (Hz) TEMPERATURE ERROR vs. DXP-DXN CAPACITANCE MAX6649 toc07 2.0 TEMPERATURE ERROR (°C) 7 MAX6649 toc08 50 VIN = AC-COUPLED TO DXN VIN = 100mVP-P 8 -1 -2 25 9 TEMPERATURE ERROR (°C) 4 TEMPERATURE ERROR (°C) 0.5 4 50 CONVERSION RATE (Hz) 1.0 0 25 0 SUPPLY VOLTAGE (V) MAX6649 toc05 3.0 MAX6649 toc06 STANDBY SUPPLY CURRENT (μA) 5.0 OPERATING SUPPLY CURRENT vs. CONVERSION RATE MAX6649 toc03 STANDBY SUPPLY CURRENT vs. SUPPLY VOLTAGE TEMPERATURE ERROR (°C) MAX6646/MAX6647/MAX6649 +145°C Precision SMBus-Compatible Remote/ Local Sensors with Overtemperature Alarms 1.000 10.000 100.000 DXP-DXN CAPACITANCE (nF) _______________________________________________________________________________________ 10k 100k +145°C Precision SMBus-Compatible Remote/ Local Sensors with Overtemperature Alarms PIN NAME FUNCTION 1 VCC Supply Voltage Input, 3V to 5.5V. Bypass VCC to GND with a 0.1µF capacitor. A 200Ω series resistor is recommended but not required for additional noise filtering. 2 DXP Combined Remote-Diode Current Source and A/D Positive Input for Remote-Diode Channel. DO NOT LEAVE DXP FLOATING; connect DXP to DXN if no remote diode is used. Place a 2200pF capacitor between DXP and DXN for noise filtering. 3 DXN Combined Remote-Diode Current Sink and A/D Negative Input. DXN is internally connected to ground. 4 OVERT 5 GND Overtemperature Alert/Interrupt Output, Open Drain. OVERT is logic low when the temperature is above the software-programmed threshold. Ground SMBus Alert (Interrupt) Output, Open Drain. ALERT asserts when temperature exceeds limits (high or low temperature). ALERT stays asserted until acknowledged by either reading the status register or by successfully responding to an alert response address, provided that the fault condition no longer exists. See the ALERT Interrupts section. 6 ALERT 7 SDA SMBus Serial-Data Input/Output, Open Drain 8 SCLK SMBus Serial-Clock Input Detailed Description The MAX6646/MAX6647/MAX6649 are temperature sensors designed to work in conjunction with a microprocessor or other intelligence in thermostatic, process-control, or monitoring applications. Communication with the MAX6646/MAX6647/MAX6649 occurs through the SMBus-compatible serial interface and dedicated alert and overtemperature outputs. ALERT asserts if the measured local or remote temperature is greater than the software-programmed ALERT high limit or less than the ALERT low limit in the MAX6649. ALERT also asserts, in the MAX6649, if the remote-sensing diode pins are shorted or unconnected. The overtemperature alarm, OVERT, asserts if the software-programmed OVERT limit is exceeded. OVERT can be connected to fans, a system shutdown, a clock throttle control, or other thermal-management circuitry. The MAX6646/MAX6647/MAX6649 convert temperatures to digital data either at a programmed rate or in single conversions. Temperature data is represented as 11 bits, with the LSB equal to 0.125°C. The “main” temperature data registers (at addresses 00h and 01h) are 8-bit registers that represent the data as 8 bits with the full-scale reading indicating the diode fault status (Table 1). The remaining 3 bits of temperature data are available in the “extended” registers at addresses 11h and 10h (Table 2). ADC and Multiplexer The averaging ADC integrates over a 60ms period (each channel, typically), 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 results of the unused channel can be ignored. If the remote-diode channel is unused, connect DXP to DXN rather than leaving the inputs open. Table 1. Main Temperature Data Register Format (00h, 01h) TEMP (°C) DIGITAL OUTPUT +145 1001 0001 +130 1000 0010 +128 1000 0000 +25 0001 1001 0 0000 0000 <0 Diode fault (short or open) 0000 0000 1111 1111 _______________________________________________________________________________________ 5 MAX6646/MAX6647/MAX6649 Pin Description MAX6646/MAX6647/MAX6649 +145°C Precision SMBus-Compatible Remote/ Local Sensors with Overtemperature Alarms The DXP-DXN differential input voltage range is 0.25V to 0.95V. Excess resistance in series with the remote diode causes +0.5°C (typ) error per ohm. Remote Temperature Measurement Range The MAX6646/MAX6647/MAX6649 measure remote temperatures significantly above the +120°C limit of many temperature sensors. External diode-connected transistors work well as temperature sensors up to approximately +145°C, where accuracy begins to degrade. Thermal diodes on some CPUs have characteristics that produce “apparent temperatures” far above actual operating temperatures. The MAX6646/ MAX6647/MAX6649 measure apparent temperatures as high as +170°C, as long as the actual temperature is less than +145°C. A/D Conversion Sequence A conversion sequence consists of a local temperature measurement and a remote temperature measurement. Each time a conversion begins, whether initiated automatically in the free-running autonomous mode (RUN = 0) or by writing a one-shot command, both channels are converted, and the results of both measurements are available after the end of a conversion. A BUSY status bit in the status byte indicates that the device is performing a new conversion. 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 12µA by disabling the ADC and timing circuitry. Enter standby mode by setting the RUN bit to 1 in the configuration byte register (Table 6). 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 Typical Operating Characteristics). In standby mode, the MAX6646/MAX6647/MAX6649 can be forced to perform A/D 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 250µA (typ). Slowing down the conversion rate reduces the average supply current (see Typical Operating Characteristics). Between conversions, the conversion rate timer consumes 25µA (typ) of supply current. In standby mode, supply current drops to 3µA (typ). 6 SMBus Digital Interface From a software perspective, the MAX6646/MAX6647/ MAX6649 appear 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 MAX6646/MAX6647/MAX6649 employ 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 register was previously selected by a read 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. Temperature data can be read 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). The MSB is transmitted first. An additional 3 bits can be read from the read external extended temperature register (10h), which extends the data to 11 bits and the resolution to 0.125°C per LSB. An additional 3 bits can be read from the read internal extended temperature register (11h), which extends the data to 11 bits and the resolution to 0.125°C per LSB (Table 2). When a conversion is complete, the main temperature register and the extended temperature register are updated simultaneously. Ensure that no conversions are completed between reading the main register and the extended register, so that both registers contain the result of the same conversion. Table 2. Extended Resolution Temperature Register Data Format (10h, 11h) FRACTIONAL TEMP (°C) DIGITAL OUTPUT 0.000 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 _______________________________________________________________________________________ +145°C Precision SMBus-Compatible Remote/ Local Sensors with Overtemperature Alarms MAX6646/MAX6647/MAX6649 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 S ADDRESS WR ACK COMMAND 7 bits ACK S 8 bits Slave Address: equivalent to chip-select line ADDRESS RD ACK Command Byte: selects which register you are reading from /// 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 ACK COMMAND 7 bits ACK P S 8 bits ADDRESS RD ACK 7 bits 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 Command Byte: sends command with no data, usually used for one-shot command S = Start condition P = Stop condition DATA 7 bits Send Byte Format S 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 tBUF I = MASTER PULLS DATA LINE LOW J = ACKNOWLEDGE CLOCKED INTO SLAVE K = ACKNOWLEDGE CLOCK PULSE L = STOP CONDITION M = NEW START CONDITION Figure 2. SMBus Write Timing Diagram To ensure valid extended data, read extended resolution temperature data using one of the following approaches: 1) Put the MAX6646/MAX6647/MAX6649 into standby mode by setting bit 6 of the configuration register to 1. Initiate a one-shot conversion using command byte 0Fh. When this conversion is complete, read the contents of the temperature data registers. 2) If the MAX6646/MAX6647/MAX6649 is in run mode, read the status byte. If the BUSY bit indicates that a conversion is in progress, wait until the conversion is complete (BUSY bit set to zero) before reading the temperature data. Following a conversion completion, immediately read the contents of the temperature data registers. If no conversion is in progress, the data can be read within a few microseconds, which is a sufficiently short period of time to ensure that a new conversion cannot be completed until after the data has been read. _______________________________________________________________________________________ 7 MAX6646/MAX6647/MAX6649 +145°C Precision SMBus-Compatible Remote/ Local Sensors with Overtemperature Alarms A tLOW B tHIGH C 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 Read Timing Diagram Alarm Threshold Registers Four registers store ALERT threshold values—one hightemperature (THIGH) and one low-temperature (TLOW) register each for the local and remote channels. If either measured temperature equals or exceeds the corresponding ALERT threshold value, the ALERT interrupt asserts. The MAX6646/MAX6647 local (internal) ALERT THIGH register POR state is 0101 0101, or +85°C, while the remote (external) ALERT THIGH register POR state is 0101 1111, or +95°C.The MAX6649 POR state of both ALERT THIGH registers is 0101 0101, or +85°C. The POR state of the local and remote T LOW registers for all devices is 0000 0000, or 0°C. Two additional registers store remote and local alarm threshold data corresponding to the OVERT output. The values stored in these registers are high-temperature thresholds. If either of the measured temperatures equals or exceeds the corresponding alarm threshold value, an OVERT output asserts. The MAX6646/MAX6647 local (internal) OVERT register POR state is 0101 0101, or +85°C, while the remote (external) OVERT register POR state is 0111 1101, or +125°C. The MAX6649 POR state of both OVERT registers is 0101 0101, or +85°C. Diode Fault Alarm A continuity fault detector at DXP 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 is loaded with 1111 1111. If the fault is an open-circuit fault bit 2 (OPEN), the status byte is set to 1. In the MAX6649, ALERT is activated at the end of the conversion. Immediately after POR, the status register indicates that no fault is present. If a fault is present upon power-up, the fault is not indicated until the end of the first conversion. 8 ALERT Interrupts The ALERT interrupt occurs when the internal or external temperature reading exceeds a high- or low-temperature limit (programmed) or in the MAX6649, when the remote diode is disconnected (for continuity fault detection). The ALERT interrupt output signal is latched and can be cleared only by either reading the status register or by successfully responding to an alert response address. In both cases, the alert is cleared if the fault condition no longer exists. Asserting ALERT does not halt automatic conversion. The ALERT output is open drain, allowing multiple devices to share a common interrupt line. The MAX6646/MAX6647/MAX6649 respond to the SMBus alert response address, an interrupt pointer return-address feature (see the Alert Response Address section). Prior to taking corrective action, always check to ensure that an interrupt is valid by reading the current temperature. Fault Queue Register In some systems, it may be desirable to ignore a single temperature measurement that falls outside the ALERT limits. Bits 1 and 2 of the fault queue register (address 22h) determine the number of consecutive temperature faults necessary to set ALERT (see Tables 3 and 4). Alert Response Address The SMBus alert response interrupt pointer provides quick fault identification for simple slave devices that lack the complex, expensive logic needed to be a bus master. Upon receiving an ALERT interrupt signal, the host master can broadcast a receive byte transmission to the alert response slave address (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. _______________________________________________________________________________________ +145°C Precision SMBus-Compatible Remote/ Local Sensors with Overtemperature Alarms BIT 7 6 to 3 NAME RFU RFU POR STATE FUNCTION 1 Reserved. Always write 1 to this bit. 0 Reserved. Always write zero to this bit. 2 FQ1 1 Fault queue-length control bit (see Table 4). 1 FQ0 1 Fault queue-length control bit (see Table 4). 0 RFU 0 Reserved. Always write zero to this bit. 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 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 read alert response protocol clears the interrupt latch, provided the condition that caused the alert no longer exists. OVERT Overtemperature Alarm/Warning Outputs OVERT asserts when the temperature rises to a value stored in one of the OVERT limit registers (19h, 20h). It deasserts when the temperature drops below the stored limit, minus hysteresis. OVERT can be used to activate a cooling fan, send a warning, invoke clock throttling, or trigger a system shutdown to prevent component damage. Command Byte Functions The 8-bit command byte register (Table 5) is the master index that points to the various other registers within the MAX6646/MAX6647/MAX6649. 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. The MAX6646/MAX6647/MAX6649 incorporate collision avoidance so that completely asynchronous operation is allowed between SMBus operations and temperature conversions. Table 4. Fault Queue Length Bit Definition FQ1 FQ0 FAULT QUEUE LENGTH (SAMPLES) 0 0 1 0 1 2 1 1 3 1 0 1 One-Shot The one-shot command immediately forces a new conversion cycle to begin. If the one-shot command is received while the MAX6646/MAX6647/MAX6649 are in standby mode (RUN bit = 1), a new conversion begins, after which the device returns to standby mode. If a oneshot conversion is in progress when a one-shot command is received, the command is ignored. If a one-shot command is received in autonomous mode (RUN 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. Configuration Byte Functions The configuration byte register (Table 6) is a read-write register with several functions. Bit 7 is used to mask (disable) interrupts. Bit 6 puts the MAX6646/MAX6647/ MAX6649 into standby mode (STOP) or autonomous (RUN) mode. Status Byte Functions The status byte register (Table 7) 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 in 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 conversion is complete and if the fault condition no longer exists. Note that the ALERT interrupt latch is not automatically cleared when the status flag bit indicating the ALERT is cleared. The fault condition must be eliminated before the ALERT output can be cleared. When autoconverting, if the THIGH and TLOW limits are close together, it is possible for both high-temp and lowtemp status bits to be set, depending on the amount of time between status read operations (especially when converting at the fastest rate). 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. _______________________________________________________________________________________ 9 MAX6646/MAX6647/MAX6649 Table 3. Fault Queue Register Bit Definition (22h) MAX6646/MAX6647/MAX6649 +145°C Precision SMBus-Compatible Remote/ Local Sensors with Overtemperature Alarms Table 5. Command-Byte Bit Assignments REGISTER ADDRESS POR STATE FUNCTION RLTS 00h 0000 0000 0°C RRTE 01h 0000 0000 0°C Read local (internal) temperature RSL 02h N/A — Read status byte RCL 03h 0000 0000 — Read configuration byte RCRA 04h 0000 0111 — Read conversion rate byte Read remote (external) temperature RLHN 05h 0101 0101 +85°C Read local (internal) ALERT high limit RLLI 06h 0000 0000 0°C Read local (internal) ALERT low limit RRHI 07h 0101 1111 +95°C Read remote (external) ALERT high limit (MAX6646/MAX6647) 0101 0101 +85°C Read remote (external) ALERT high limit (MAX6649) RRLS 08h 0000 0000 0°C WCA 09h N/A — Read remote (external) ALERT low limit Write configuration byte WCRW 0Ah N/A — Write conversion rate byte WLHO 0Bh N/A — Write local (internal) ALERT high limit WLLM 0Ch N/A — Write local (internal) ALERT low limit WRHA 0Dh N/A — Write remote (external) ALERT high limit WRLN 0Eh N/A — Write remote (external) ALERT low limit OSHT 0Fh N/A — One-shot REET 10h 0000 0000 0°C Read remote (external) extended temperature RIET 11h 0000 0000 0°C Read local (internal) extended temperature RWOE 19h 0111 1101 +125°C Read/write remote (external) OVERT limit (MAX6646/MAX6647) 0101 0101 +85°C Read/write remote (external) OVERT limit (MAX6649) RWOI 20h 0101 0101 +85°C HYS 21h 0000 1010 10°C Read/write local (internal) OVERT limit Overtemperature hysteresis QUEUE 22h 1000 0110 — Fault queue — FEh 0100 1101 — Read manufacture ID — FFh 0101 1001 — Read revision ID Table 6. Configuration-Byte Bit Assignments (03h) BIT NAME POR STATE FUNCTION 7 (MSB) MASK 0 Masks ALERT interrupts when set to 1. 6 RUN 0 Standby mode control bit; if set to 1, standby mode is initiated. 5 to 0 RFU 0 Reserved. Conversion Rate Byte The conversion rate register (Table 8) programs the time interval between conversions in free-running autonomous mode (RUN = 0). This variable rate control can be used to reduce the supply current in portable-equipment applications. The conversion rate byte’s POR state is 07h or 4Hz. The MAX6646/MAX6647/MAX6649 look only at the 3 LSBs of this register, so the upper 5 bits are “don’t care” bits, which should be set to zero. The conversion rate tolerance is ±25% at any rate setting. 10 Valid A/D conversion results for both channels are available two total conversion times (250ms nominal, 312ms maximum) after initiating a conversion, whether conversion is initiated through the RUN bit, one-shot command, or initial power-up. Changing the conversion rate can also affect the delay until new results are available. ______________________________________________________________________________________ +145°C Precision SMBus-Compatible Remote/ Local Sensors with Overtemperature Alarms BIT NAME POR STATE 7 (MSB) BUSY 0 A/D is busy converting when 1. 6 LHIGH 0 Local (internal) high-temperature alarm has tripped when 1; cleared by POR or readout of the status byte if the fault condition no longer exists. 5 LLOW 0 Local (internal) low-temperature alarm has tripped when 1; cleared by POR or readout of the status byte if the fault condition no longer exists. 4 RHIGH 0 Remote (external) high-temperature alarm has tripped when 1; cleared by POR or readout of the status byte if the fault condition no longer exists. 3 RLOW 0 Remote (external) low-temperature alarm has tripped when 1; cleared by POR or readout of the status byte if the fault condition no longer exists. 2 FAULT 0 A 1 indicates DXN and DXP are either shorted or open; cleared by POR or readout of the status byte if the fault condition no longer exists. 1 EOT 0 A 1 indicates the remote (external) junction temperature exceeds the external OVERT threshold. 0 IOT 0 A 1 indicates the local (internal) junction temperature exceeds the internal OVERT threshold. FUNCTION Slave Addresses The MAX6646/MAX6647/MAX6649 have fixed slave addresses (see Table 9). All devices also respond to the SMBus alert response slave address (see the Alert Response Address section). Table 8. Conversion-Rate Control Byte (04h) DATA CONVERSION RATE (Hz) POR and UVLO 00h 0.0625 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 2.0V (typ). When power is first applied and VCC rises above 2.0V (typ), the logic blocks begin operating, although reads and writes at VCC levels below 3V are not recommended. A second VCC comparator, the ADC UVLO comparator, prevents the ADC from converting until there is sufficient headroom (VCC = 2.7V typ). 01h 0.125 02h 0.25 03h 0.5 04h 1 05h 2 06h 4 07h 4 08h-FFh Reserved Power-Up Defaults Power-up defaults include: • Interrupt latch is cleared. • ADC begins autoconverting at a 4Hz rate. • Command byte is set to 00h to facilitate quick local temperature receive byte queries. • Local (internal) THIGH limit is set to +85°C. • Local (internal) TLOW limit is set to 0°C. • Remote (external) T HIGH limit is set to +85°C (MAX6649)/+95°C (MAX6646/MAX6647) • OVERT (internal) limit is set to +85°C • OVERT (external) limit is set to +85°C (MAX6649)/ +125°C (MAX6646/MAX6647) Table 9. Slave Addresses PART SLAVE ADDRESS MAX6646 1001 101 MAX6647 1001 110 MAX6649 1001 100 ______________________________________________________________________________________ 11 MAX6646/MAX6647/MAX6649 Table 7. Status Register Bit Assignments (02h) MAX6646/MAX6647/MAX6649 +145°C Precision SMBus-Compatible Remote/ Local Sensors with Overtemperature Alarms Applications Information 90 Ω = 0.453 °C μV Ω 198.6 °C Remote-Diode Selection The MAX6646/MAX6647/MAX6649 can directly measure the die temperature of CPUs and other ICs that have on-board temperature-sensing diodes (see 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 MAX6646/MAX6647/MAX6649 are optimized for n = 1.008, which is the typical value for the Intel® Pentium® III and the AMD Athlon MP model 6. If a sense transistor with a different ideality factor is used, the output data is different. 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. As mentioned above, the nominal ideality factor of the MAX6646/MAX6647/MAX6649 is 1.008. The following example uses the MAX6646/MAX6647/MAX6649 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 ⎜ ⎟ = TM (1.00599) ⎝ 1.002 ⎠ n1 ⎝ ⎠ For a real temperature of +85°C (358.15 K), the measured temperature is +82.91°C (356.02 K), which is 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, change in the measured voltage is: ΔVM = RS (100μA − 10μA) = 90μA × RS μV Assume that the diode being measured has a series resistance of 3Ω. The series resistance contributes an offset of: 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 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, short the collector to the base. Table 10 lists examples of discrete transistors that are appropriate for use with the MAX6646/MAX6647/MAX6649. Avoid violating the A/D input voltage range by using a small-signal transistor with a relatively high forward voltage. The forward voltage at the highest expected temperature must be greater than 0.25V at 10µA, and the forward voltage at the lowest expected temperature must be less than 0.95V at 100µA. Do not use large power transistors. 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. Table 10. Remote-Sensor Transistor Manufactures MANUFACTURER MODEL NO. Central Semiconductor (USA) CMPT3904 Rohm Semiconductor (USA) SST3904 Samsung (Korea) Since 1°C corresponds to 198.6µV, series resistance contributes a temperature offset of: Intel and Pentium are registered trademarks of Intel Corp. AMD and Athlon are trademarks of Advanced Micro Devices, Inc. 12 KST3904-TF Siemens (Germany) Zetex (England) SMBT3904 FMMT3904CT-ND Note: Discrete transistors must be diode connected (base shorted to collector). ______________________________________________________________________________________ +145°C Precision SMBus-Compatible Remote/ Local Sensors with Overtemperature Alarms 10 MILS 10 MILS DXP 10 MILS DXN MINIMUM 10 MILS GND Figure 4. Recommended DXP-DXN PC Traces 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 PC board layout and proper external noise filtering. High-frequency EMI is best filtered at DXP and DXN with an external 2200pF capacitor. Larger capacitor values can be used for added filtering, but do not exceed 3300pF because larger values can introduce errors due to the rise time of the switched current source. PC Board Layout Follow these guidelines to reduce the measurement error of the temperature sensors: 1) Place the MAX6646/MAX6647/MAX6649 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 ISA/PCI buses. 2) Do not route the DXP-DXN lines next to the deflection coils of a CRT. Also, do not route the traces across fast digital signals, which can easily introduce 30°C error, even with good filtering. 3) Route the DXP and DXN traces in parallel and in close proximity to each other, away from any higher voltage traces, such as 12VDC. 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 4). 4) Route through as few vias and crossunders as possible to minimize copper/solder thermocouple effects. 5) When introducing a thermocouple, make sure that both the DXP and the DXN paths have matching thermocouples. A copper-solder thermocouple exhibits 3µV/°C, and takes about 200µV of voltage error at DXP-DXN to cause a 1°C measurement error. Adding a few thermocouples causes a negligible error. 6) Use wide traces. Narrow traces are more inductive and tend to pick up radiated noise. The 10mil 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. 7) Add a 200Ω resistor in series with VCC for best noise filtering (see Typical Operating Circuit). 8) 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 distance 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 0.5°C. Thermal Mass and Self-Heating When sensing local temperature, these devices are intended to measure the temperature of the PC board to which the devices are soldered. The leads provide a good thermal path between the PC board 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 PC board is far greater than that of the MAX6646/MAX6647/MAX6649, the device follows temperature changes on the PC board with little or no perceivable delay. ______________________________________________________________________________________ 13 MAX6646/MAX6647/MAX6649 GND MAX6646/MAX6647/MAX6649 +145°C Precision SMBus-Compatible Remote/ Local Sensors with Overtemperature Alarms 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 sensors, smaller packages, such as SC70s or 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. 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 a 4Hz conversion rate and with ALERT sinking 1mA, the typical power dissipation is: 5.0V x 500µA + 0.4V x 1mA = 2.9mW ø J-A for the 8-pin µMAX package is +221°C/W, so assuming no copper PC board heat sinking, the resulting temperature rise is: ΔT = 2.9mW x +221°C/W = +0.6409°C Even under nearly worst-case conditions, it is difficult to introduce a significant self-heating error. Functional Diagram VCC MAX6646/MAX6647/MAX6649 2 DXP MUX REMOTE DXN CONTROL LOGIC ADC LOCAL DIODE FAULT SMBus ALERT S Q 8 READ 8 WRITE SDA SCLK R REGISTER BANK 7 COMMAND BYTE REMOTE TEMPERATURE OVERT S Q R ADDRESS DECODER LOCAL TEMPERATURE ALERT THRESHOLD ALERT RESPONSE ADDRESS GND 14 OVERT THRESHOLD ______________________________________________________________________________________ +145°C Precision SMBus-Compatible Remote/ Local Sensors with Overtemperature Alarms POR VALUES ALERT ASSERTED WHILE DIODE OPEN PKG CODE +95 No U8-1 +95 No U8-1 +85 Yes U8-1 PART ADDRESS EXTERNAL OVERT LIMIT (°C) EXTERNAL ALERT THIGH LIMIT (°C) MAX6646 1001 101 +125 MAX6647 1001 110 +125 MAX6649 1001 100 +85 Pin Configuration Chip Information TRANSISTOR COUNT: 14,764 PROCESS: BiCMOS TOP VIEW VCC 1 DXP 2 DXN 3 OVERT 4 8 MAX6646 MAX6647 MAX6649 SCLK 7 SDA 6 ALERT 5 GND μMAX ______________________________________________________________________________________ 15 MAX6646/MAX6647/MAX6649 Selector Guide Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) 4X S 8 8 INCHES DIM A A1 A2 b E Ø0.50±0.1 H c D e E H 0.6±0.1 L 1 1 α 0.6±0.1 S BOTTOM VIEW D MIN 0.002 0.030 MAX 0.043 0.006 0.037 0.014 0.010 0.007 0.005 0.120 0.116 0.0256 BSC 0.120 0.116 0.198 0.188 0.026 0.016 6° 0° 0.0207 BSC 8LUMAXD.EPS MAX6646/MAX6647/MAX6649 +145°C Precision SMBus-Compatible Remote/ Local Sensors with Overtemperature Alarms MILLIMETERS MAX MIN 0.05 0.75 1.10 0.15 0.95 0.25 0.36 0.13 0.18 2.95 3.05 0.65 BSC 2.95 3.05 4.78 5.03 0.41 0.66 0° 6° 0.5250 BSC TOP VIEW A1 A2 A α c e b L SIDE VIEW FRONT VIEW PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE, 8L uMAX/uSOP APPROVAL DOCUMENT CONTROL NO. 21-0036 REV. J 1 1 Revision History Pages changed at Rev 3: 1, 2, 9, 10, 15, 16 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. 16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.