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| 19-3895; Rev 1; 1/06 Temperature Monitor with Dual Serial Interface General Description The MAX6638 thermal-management sensor includes internal (local) and external (remote) digital temperature sensors and two independent SMBusTM serial ports. The remote temperature accuracy is 1.0C, and the local temperature accuracy is 2C. The MAX6638 also features extended temperature resolution data available in 0.125C increments. The MAX6638 provides three system alarms: channel 1 alert (ALERT1), overtemperature (OVERT1), and channel 2 alert (ALERT2) that contain programmable thresholds set independently by each of the SMBus serial ports (SMBus1 and SMBus2). Each alert output asserts when any of four temperature conditions is violated: local overtemperature, remote overtemperature, local undertemperature, or remote undertemperature. The overtemperature signal asserts when the temperature rises above the value in the overtemperature limit register. Use the OVERT1 output to activate a cooling fan or trigger a system shutdown. Each of the 2-wire serial-interface ports accepts standard System Management Bus (SMBus) write byte, read byte, send byte, and receive byte commands independently of one another with total collision avoidance handled by the MAX6638. Each SMBus can operate its own unique serial-data rate to access any register in the MAX6638 for data reads or data writes. The MAX6638 manages all dual-port data register access functions providing a seamless, conflict-free integration into a multimaster architecture for thermal management. The MAX6638 performs measurements autonomously, at the programmed conversion rate, or in a single-conversion mode. Each SMBus port can set the conversion rate with the higher conversion and update rate dominating the average power-supply current. Single-conversion requests have a maximum delay of two conversion cycles with channel-conversion management and cycling regulated by the dual-port controller. The MAX6638 operating temperature range is -40C to +125C and measures temperatures between 0C and +145C. The MAX6638 is available in a 16-pin, 4mm x 4mm TQFN with exposed paddle package. Two Independent Interfaces with Collision Avoidance Features SMBus/I 2C*-Compatible High Accuracy 1.0C from +85C to +100C (Remote) Remote and Local Temperature Measurements Three Programmable Output Alarms: ALERT1, OVERT1, and ALERT2 Programmable Conversion Rates 11-Bit Low-Noise Integrating ADC No Calibration Required Autoscan Conversions MAX6638 Ordering Information PART MAX6638ATE+ TEMP RANGE -40C to +125C PINPACKAGE 16 TQFN-EP* (4mm x 4mm) PKG CODE T1644-4 *EP = Exposed paddle. +Denotes lead-free package. Pin Configuration SCK1 N.C. SDA1 10 TOP VIEW 12 11 ALERT1 9 N.C. 13 ALERT2 14 SDA2 15 SCK2 16 8 7 GND N.C. I.C. N.C. MAX6638 6 5 + 1 VCC 2 DXP 3 DXN 4 OVERT1 Applications Graphics Cards Notebook Computers Computer Motherboard Systems Desktop Computers Workstations TQFN-EP Typical Operating Circuit appears at end of data sheet. SMBus is a trademark of Intel Corporation. *Purchase of I 2C components from Maxim Integrated Products, Inc., or one of its sublicensed Associated Companies, conveys a license under the Philips I 2C Patent Rights to use these components in an I 2C system, provided that the system conforms to the I 2C Standard Specification as defined by Philips. 1 ________________________________________________________________ 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. Temperature Monitor with Dual Serial Interface MAX6638 ABSOLUTE MAXIMUM RATINGS (All voltages referenced to GND, unless otherwise noted.) VCC ....................................................................................-0.3V to +6.0V DXP.............................................................-0.3V to (VCC + 0.3V) DXN .......................................................................-0.3V to +0.8V SCK1, SDA1, SCK2, SDA2, ALERT1, OVERT1, ALERT2 .....................................................-0.3V to +6V SDA1, SDA2, ALERT1, OVERT1, ALERT2 ..........-1mA to +50mA DXN Current .......................................................................1mA Continuous Power Dissipation (TA = +70C) 16-Pin TQFN (derate 16.9 mW/C above +70C) ....1349 mW ESD Protection (all pins, Human Body Model) ................2000V Operating Temperature Range .........................-40C to +125C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VCC = 3.0V to 5.5V, TA = -40C to +125C, unless otherwise noted. Typical values are at VCC = 3.3V and TA = +85C.) (Note 1) PARAMETER Supply Voltage Operating Current Standby Supply Current TEMPERATURE MEASUREMENT Remote Diode-Source Current IRJ High level Low level VCC = 3.3V, TA = +85C to +100C, TRJ = +85C to +145C Remote Temperature Error VCC = 3.3V, TA = +25C to +100C, TRJ = +25C to +145C VCC = 3.3V, TA = +0C to +125C, TRJ = 0C to +145C Local Temperature Error Supply Sensitivity of Temperature Error POWER-ON RESET Power-On-Reset Threshold POR Threshold Hysteresis Undervoltage-Lockout Threshold Undervoltage-Lockout Hysteresis ANALOG-TO-DIGITAL CONVERTER Conversion Time ALERT1, OVERT1, ALERT2, SDA1, SDA2 Output Low Voltage Leakage Current VOL ILEAK IOL = 6mA VOH = 5.5V 0.6 1 V A Nonoverlapping single conversion from stop bit to conversion complete 23 32 39 ms VCC falling 2.30 VCC falling 1.9 90 2.60 90 2.95 V mV V mV VCC = 3.3V, TA = +25C to +85C VCC = 3.3V, TA = 0C to +125C 80 8 -1.0 -2.0 -3.0 -2.0 -3.5 0.2 100 10 120 12 +1.0 +2.0 +3.0 +2.0 +3.5 C C/V C A SYMBOL VCC During conversion ADC not converting SMBus1 and SMBus2 static 3 CONDITIONS MIN 3.0 600 TYP MAX 5.5 950 80 10 UNITS V A A 2 _______________________________________________________________________________________ Temperature Monitor with Dual Serial Interface ELECTRICAL CHARACTERISTICS (continued) (VCC = 3.0V to 5.5V, TA = -40C to +125C, unless otherwise noted. Typical values are at VCC = 3.3V and TA = +85C.) (Note 1) PARAMETER Logic Input Low Voltage Logic Input High Voltage Input Leakage Current Input Capacitance Serial-Clock Frequency Bus Free Time Between STOP and START Condition START Condition Setup Time Repeat START Condition Setup Time START Condition Hold Time STOP Condition Setup Time Clock Low Period Clock High Period Data Setup Time Data Hold Time SMBus Rise Time SMBus Fall Time SMBus Timeout tSU:STA tHD:STA tSU:STO tLOW tHIGH tSU:DAT tHD:DAT tR tF tTIMEOUT SDA_ low period for interface reset 30 45 (Note 4) 90% of SCK_ to 90% of SDA_ 10% of SDA_ to 90% of SCK_ 90% of SCK_ to 90% of SDA_ 10% to 10% 90% to 90% SYMBOL VIL VIH ILEAK CIN fSCK tBUF (Note 3) 4.7 4.7 50 4 4 4.7 4.0 250 300 1 300 60 VIN = GND or VCC 5 100 2.1 1 CONDITIONS MIN TYP MAX 0.8 UNITS V V A pF kHz s s ns s s s s ns ns s ns ms SMBus INTERFACE (SCK1, SCK2, SDA1, SDA2) MAX6638 SMBus-COMPATIBLE TIMING (Figure 5) (Note 2) Note 1: Note 2: Note 3: Note 4: All parameters are tested at a single temperature. Specifications over temperature are guaranteed by design. Timing specifications are guaranteed by design. Each serial interface resets when its SCK_ is low for more than tTIMEOUT. A transition must internally provide at least a hold time to bridge the unidentified region (300ns max) of SCK_'s falling edge. _______________________________________________________________________________________ 3 Temperature Monitor with Dual Serial Interface MAX6638 Typical Operating Characteristics (VCC = 3.3V, TA = +25C, unless otherwise noted.) STANDBY SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX6638 toc01 AVERAGE SUPPLY CURRENT vs. CONVERSION RATE MAX6638 toc02 OPERATING SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX6638 toc03 7 6 SUPPLY CURRENT (A) 5 4 3 2 1 0 3.0 3.5 4.0 4.5 5.0 TA = -40C TA = +25C TA = +85C 600 500 SUPPLY CURRENT (A) 400 300 200 100 0 700 650 SUPPLY CURRENT (A) 600 550 500 TA = -40C 450 400 TA = +25C TA = +85C 5.5 0 5 10 15 20 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) CONVERSION RATE (Hz) SUPPLY VOLTAGE (V) REMOTE TEMPERATURE ERROR vs. REMOTE DIODE TEMPERATURE MAX6638 toc04 LOCAL TEMPERATURE ERROR vs. DIE TEMPERATURE MAX6638 toc05 TEMPERATURE ERROR vs. POWER-SUPPLY NOISE FREQUENCY MAX6638 toc06 0.8 REMOTE TEMPERATURE ERROR (C) 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 0 20 100 120 80 REMOTE DIODE TEMPERATURE (C) 40 60 0 LOCAL TEMPERATURE ERROR (C) -0.5 -1.0 -1.5 -2.0 -2.5 -3.0 6 LOCAL TEMPERATURE ERROR (C) 4 2 0 REMOTE 140 0 20 40 60 80 100 120 140 -2 0.01 0.1 1 10 100 1,000 10,000 DIE TEMPERATURE (C) POWER-SUPPLY NOISE FREQUENCY (kHz) LOCAL TEMPERATURE ERROR vs. COMMON-MODE NOISE FREQUENCY MAX6638 toc07 REMOTE TEMPERATURE ERROR vs. DXP-DXN CAPACITANCE MAX6638 toc08 0 LOCAL TEMPERATURE ERROR (C) -1 -2 -3 -4 -5 -6 0.01 2 REMOTE TEMPERATURE ERROR (C) 0 -2 -4 -6 -8 0.1 1 10 100 1,000 10,000 0.01 0.1 1 10 100 COMMON-MODE NOISE FREQUENCY (kHz) DXP-DXN CAPACITANCE (nF) 4 _______________________________________________________________________________________ Temperature Monitor with Dual Serial Interface Pin Description PIN 1 2 3 4 5, 7, 12, 13 6 8 9 10 11 14 15 16 EP NAME VCC DXP DXN OVERT1 N.C. I.C. GND ALERT1 SDA1 SCK1 ALERT2 SDA2 SCK2 GND FUNCTION Supply Voltage. Bypass VCC to GND with a 0.1F capacitor. A 47 series resistor is recommended for additional noise filtering, but not required. Combined Current Source and ADC Positive Input for Remote Diode. If a remote-sensing junction is not used, connect DXP to DXN. Combined Current Sink and ADC Negative Input for Remote Diode. DXN is internally biased to a diode voltage above ground. Digital Open-Drain Output. OVERT1 indicates an overtemperature condition on channel 1. No Connection. Not connected internally. Internally Connected. I.C. must be connected to GND. Power-Supply Ground Digital Open-Drain Output. ALERT1 indicates alert condition on channel 1. SMBus Data Channel 1. Open-drain output. SMBus Clock Channel 1 Digital Open-Drain Output. ALERT2 indicates alert condition on channel 2. SMBus Data Channel 2. Open-drain output. SMBus Clock Channel 2 Ground. Connect to ground. MAX6638 Detailed Description The MAX6638 temperature monitor features dual-port SMBus access for use in thermal management of graphics processing unit (GPU) and CPU systems. Each of the two SMBus serial ports can be accessed independently by two thermal-monitoring systems with all dual-port collision-avoidance logic controlled by the MAX6638. Each SMBus thermal-monitoring channel (channels 1 and 2) has a corresponding over/undertemperature ALERT_ open-drain output with independently configurable limit registers. Channel 1 includes an overtemperature indicator (OVERT1) with an initial set-point limit that is always activated after a power-on reset (POR). The initial OVERT1 set point can be overwritten after POR by SMBus1 serial programming. The overtemperature alarm OVERT1 asserts if the set-point limit is exceeded. temperature conversion results of the two temperature channels are in integer format. The MSBs of the temperature data are in 8-bit registers (addresses 00h and 01h; see Table 1) that represent the data as 8 bits with the full-scale reading to indicate a diode fault. The remaining 3 bits of temperature data are available in the extended data-registers format with the LSB equal to +0.125C (addresses 11h and 10h; see Table 2). The converted readings are stored in SMBus reading registers along with the limit-value registers and other control functions. Table 1. Temperature Data Format (RLTS1, RRTS1, RLTS2, RRTS2) TEMPERATURE (C) +145 +130 +128 +25 0 <0 Diode fault DIGITAL OUTPUT (hex) 91 82 80 19 00 00 FF DIGITAL OUTPUT (bin) 1001 0001 1000 0010 1000 0000 0001 1001 0000 0000 0000 0000 1111 1111 ADC and Multiplexer The MAX6638 converts temperatures to digital data either at a programmed rate or in single conversions. Either SMBus controller can set the programmed rate with the higher rate setting taking precedence. The MAX6638 begins conversions at the maximum rate after POR to provide the OVERT1 output signal assertion for temperatures exceeding the set-point limit. The _______________________________________________________________________________________ 5 Temperature Monitor with Dual Serial Interface MAX6638 Functional Diagram VCC MUX DXP DXN REMOTE ADC LOCAL CONTROL LOGIC SMBus 8 8 ALERT1 Q S R REGISTER BANK1 COMMAND BYTE REMOTE TEMPERATURE OVERT1 Q S R LOCAL TEMPERATURE ALERT THRESHOLD ALERT-RESPONSE ADDRESS ALERT2 Q S R 8 8 REGISTER BANK2 COMMAND BYTE 7 OVERT THRESHOLD ADDRESS DECODER 7 READ WRITE SDA1 SCK1 SMBus READ WRITE SDA2 SCK2 MAX6638 REMOTE TEMPERATURE LOCAL TEMPERATURE ALERT THRESHOLD ALERT-RESPONSE ADDRESS ADDRESS DECODER 6 _______________________________________________________________________________________ Temperature Monitor with Dual Serial Interface The averaging ADC integrates over a 16ms period (each channel, typical) 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 temperature sensors automatically convert once the conversion process starts, either in free-running (RUN = 0) or single-shot mode. 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 when the ADC is busy. If one of the two temperature sensors is not used, the MAX6638 still performs both measurements and ignores the results of the unused channel. When not using the remote-diode temperature sensor, connect DXP to DXN. The DXP-DXN differential input voltage range is 0.25V to 0.95V. Excess resistance in series with the remote diode causes a +0.5C (typ) error per ohm. The MAX6638 initiates conversion cycling after POR, after exiting standby mode from either SMBus channel, and upon one-shot request from either SMBus channel. One conversion cycle consists of two ADC conversions (one for the local temperature, one for the remote temperature), a diagnostic check on the remote temperature sensor, loading of data into the read registers, setting diagnostic flags, and setting ALERT1, ALERT2, and OVERT1, as required. Figure 1 shows the simplified timing sequence. MAX6638 Table 2. Extended Temperature Data (RLET1, RRET1, RLET2, RRET2) FRACTIONAL TEMPERATURE (C) 0.000 0.125 0.250 0.375 0.500 0.675 0.750 0.875 DIGITAL OUTPUT (bin) 000X XXXX 001X XXXX 010X XXXX 011X XXXX 100X XXXX 101X XXXX 110X XXXX 111X XXXX ONE CONVERSION CYCLE ADC LOCAL TEMPERATURE ADC AND DIAGNOSTIC REMOTE TEMPERATURE START CONVERSION UPDATE REGISTERS DATA AVAILABLE TIME Figure 1. One Complete ADC Conversion Cycle CRCn 06h START CONVERSION 250 500 750 1000 1250 1500 1750 2000 TIME (ms) ONE CONVERSION CYCLE 05h 04h 03h 02h Figure 2. Repeating ADC Conversion Cycles for Various Conversion Rate Settings _______________________________________________________________________________________ 7 Temperature Monitor with Dual Serial Interface MAX6638 SMBus1 START CONVERSION SMBus1 CRC1 = 06h CYCLE 250 CYCLE SMBus1 DATA AVAILABLE SMBus2 CRC2 = 05h CYCLE SMBus2 START CONVERSION ACTUAL DATA READY FROM ADC CONVERSIONS ACTUAL DATA READ BY SMBus2 CYCLE CYCLE CYCLE 500 CYCLE 750 CYCLE 1000 CYCLE 1250 CYCLE 1500 CYCLE 1750 CYCLE 2000 CYCLE TIME (ms) SHADED BOXES INDICATE EXPECTED ADC CONVERSION CYCLING AND DATA READINGS OF SMBus2 FROM START CONVERSION Figure 3. An Example of ADC Cycling for Two Conversion Rates Set by Each Controllers on SMBus1 and SMBus2 The MAX6638 allows conversion rates that are 2x multiples of the minimum rate of 0.0625Hz. Figure 2 shows several different conversion rate settings. The ADC converts at the higher rate of the two conversions set by SMBus1 and SMBus2 controllers. The controller that sets the higher rate receives a new conversion at the higher conversion-rate time. The controller that sets the lower rate receives the most recent conversion result at the lower conversion-rate timing. Figure 3 shows an example of this. SMBus1 initiates the ADC converter by selecting conversion rate 06h (4Hz) prior to SMBus2 initiating a conversion. Then SMBus2 initiates conversions of 05h (2Hz) independent of the process initiated by SMBus1. The controller accesses data at its programmed time set by the initiated conversion time. The data presented to SMBus2 is always ready at the anticipated time, but the data is actually the result of a previous conversion sequence driven by the higher conversion rate set by SMBus1. The first SMBus channel that activates a conversion sequence always establishes the MAX6638 conversion cycling. The ADC conversion rates increase and decrease as set by each of the SMBus controllers with the higher conversion rate always dominating. Increasing the conversion rate with the ADC cycling increases the rate the MAX6638 performs cycles without losing sync of the previously established cycle timing. A decrease in conversion rate reduces the ADC cycling to the lower rate without losing sync with the previously set cycle pattern. The ADC cycling pattern is only reset following a POR event or upon exiting the standby mode through one of the SMBus controllers' initiation of cycling or single-shot conversion. Low-Power Standby Mode Standby mode reduces the supply current to 3A (typ) by disabling the ADC and timing circuitry when both SMBus controller channels enable standby mode. Standby mode is enabled only when both SMBus controllers request standby mode. Set each of the RUN bits to 1 in each corresponding configuration register (see Tables 3 and 5) to enter standby mode. When one SMBus controller channel is set to standby mode, the other conversion rate is automatically set to the active channel's conversion rate and mode. The MAX6638 retains all data in the registers and each SMBus interface is active and listening for SMBus commands. Standby mode is not a shutdown mode. With activity on either SMBus, the device draws more supply current (see the Typical Operating Characteristics). In standby mode, the MAX6638 performs an ADC conversion sequence through the one-shot command, regardless of either of the RUN bit statuses, upon receipt of a oneshot command from either SMBus controller. If the device receives standby commands from both SMBus controllers during a conversion, the conversion cycle truncates, and the data from that conversion is not latched into a temperature register. The previous data does not change and remains available. Supply current drawn during the 32ms conversion period is 800A (typ). Slowing down the conversion rate reduces the average supply current (see the Typical Operating Characteristics). Between conversions, the conversion rate timer consumes 40A (typ) of supply current. SMBus Interface From a software perspective, the MAX6638 appears as a set of byte-wide registers that contain temperature data, 8 _______________________________________________________________________________________ Temperature Monitor with Dual Serial Interface threshold limit values, and control. A standard SMBus 2-wire serial interface is used to read temperature data, write control bits, and set threshold data. The MAX6638 employs four standard SMBus protocols: write byte, read byte, send byte, and receive byte (Figure 4). Read the temperature data from the read internal temperature (00h) and read external temperature (01h) registers of each SMBus channel. The temperature data format for these registers is 8 bits for each temperature-sensor channel, with the LSB representing 1C (Table 1). The temperature data transmits MSB first. The external extended-temperature register (10h) provides additional 3 bits, extending the data to 11 bits and the resolution to 0.125C per LSB (Table 2). The main temperature register and the extended temperature registers update simultaneously upon completion of a conversion. To ensure the registers contain the results of the same conversion of the main temperature data (MSBs) and the extended temperature data (LSBs), read the data before a new conversion completes. (TLOW_) limit register each for the local and remote temperature sensors. If either measured temperature equals or exceeds the corresponding ALERT_ threshold value, the ALERT_ output asserts. The MAX6638 local ALERT_ THIGH_ register POR state is 0101 0101, which corresponds to +85C, while the remote ALERT_ THIGH_ register POR state is 0101 1111, which corresponds to +95C. The POR state of the local and remote TLOW_ registers for all devices is 0000 0000, corresponding to 0C. Two additional registers store remote and local alarm threshold data corresponding to the OVERT1 output accessible only through SMBus1. The MAX6638 stores high-temperature thresholds in these registers. If either of the measured temperatures equals or exceeds the corresponding alarm threshold value, the OVERT1 output asserts. The MAX6638 local OVERT1 register POR state is 0101 0101, corresponding to +85C, while the remote OVERT1 register POR state is 0111 1101, corresponding to +125C. MAX6638 Alarm-Threshold Registers Four registers store ALERT threshold values: one high temperature (THIGH_) and one low temperature Write Byte Format S ADDRESS 7 bits Slave Address: equivalent to chip-select line of a 3-wire interface Read Byte Format S ADDRESS 7 bits Slave Address: equivalent to chip-select line Send Byte Format S ADDRESS 7 bits WR ACK COMMAND 8 bits Command Byte: sends command with no data, usually used for one-shot command S = Start condition P = Stop condition Figure 4. SMBus Protocols Shaded = Slave transmission /// = Not acknowledged ACK P WR ACK COMMAND 8 bits Command Byte: selects from which register you are reading ACK S WR ACK Diode Fault A continuity fault detector at DXP detects an open circuit between DXP and DXN, or a DXP short to VCC, COMMAND 8 bits ACK DATA 8 bits ACK P 1 Command Byte: selects to which register you are writing Data Byte: data goes into the register set by the command byte (to set thresholds, configuration masks, and sampling rate) RD ACK DATA 8 bits Data Byte: reads from the register set by the command byte /// P ADDRESS 7 bits Slave Address: repeated due to change in dataflow direction Receive Byte Format S ADDRESS 7 bits RD ACK DATA 8 bits /// P 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 _______________________________________________________________________________________ 9 Temperature Monitor with Dual Serial Interface MAX6638 A tLOW B tHIGH C D E F G 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: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 = MASTER PULLS DATA LINE LOW J = ACKNOWLEDGE CLOCKED INTO SLAVE K = ACKNOWLEDGE CLOCK PULSE L = STOP CONDITION M = NEW START CONDITION tSU:STO tBUF Figure 5. SMBus Write Timing Diagram A tLOW B tHIGH C D E F G H I J K L M SMBCLK SMBDATA tSU:STA tHD:STA tSU:DAT tHD:DAT 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 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 Figure 6. SMBus Read Timing Diagram GND, or DXN. If an open or short exists, each of the external temperature registers contains 1111 1111. When an open-circuit fault occurs, bit 2 (OPEN) in the status byte sets to 1. If a fault is present upon powerup, the fault is not indicated until the end of the first conversion cycle. drain ALERT_ outputs allow multiple devices to share a common interrupt line. The MAX6638 responds to the SMBus alert-response address, an interrupt pointer return-address feature. Prior to taking corrective action, always check to ensure that an interrupt is valid by reading the current temperature. ALERT_ Interrupts The ALERT_ interrupt occurs when the internal or external temperature reading exceeds a high- or low-temperature limit (programmed). The ALERT_ output signal latches and can only clear by either reading the status register or by successfully responding to an alertresponse address. In both cases, the alert clears if the temperature fault condition no longer exists. Asserting ALERT_ does not halt automatic conversion. The open- Alert Fault-Queue Register In some systems, it is 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_. Alert-Response Address The SMBus alert-response interrupt pointer provides quick fault identification for simple slave devices that 10 ______________________________________________________________________________________ Temperature Monitor with Dual Serial Interface lack the complex 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 generating an interrupt attempts to identify itself by putting its own address on the bus. The alert response can activate several different slave devices simultaneously. 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 response and continues to hold the ALERT_ line low until cleared. Successful completion of the read alertresponse protocol clears the interrupt latch, provided the condition that caused the alert no longer exists. One-Shot Conversion Cycle The one-shot command immediately forces a new conversion cycle to begin. If the MAX6638 receives a oneshot command while the MAX6638 is in standby mode (RUN = 1), a new conversion begins, after which the device returns to standby mode. If during a conversion the MAX6638 receives a one-shot command, the MAX6638 ignores the command; however, the results of the conversion in progress update the data registers accordingly. MAX6638 Configuration-Byte Functions The configuration-byte register (Tables 3 and 5) is a read-write register with several functions. Bit 7 masks interrupts. Bit 6 puts the MAX6638 into a standby (STOP) mode or autonomous (RUN) mode. The MAX6638 enters standby mode when both SMBus controllers set the corresponding configuration bits. Overtemperature Limit Output OVERT1 asserts when the temperature rises to a value stored in one of the OVERT1 limit registers (19h and 20h). It deasserts when the temperature drops below the stored limit, minus hysteresis. OVERT1 can be used to activate a cooling fan, send a warning, invoke clock throttling, or trigger a system shutdown to prevent component damage. Status-Byte Functions The status-byte register (Tables 3 and 4) indicates when any temperature threshold is exceeded. This byte also indicates whether the ADC is converting and if there is a fault detected in the external sense diode. After POR, the state of the flag bits are zero, assuming no alarm conditions are present. The status byte clears with any successful read of the status byte, after completion of a conversion and if the fault condition no longer exists. Note that the ALERT_ interrupt latch does not automatically clear when the status-flag bit indicating the ALERT_ clears. Command-Byte Functions The 8-bit command-byte register (Table 3) is the master index that points to the various other registers within the MAX6638. 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. Registers The internal registers of the MAX6638 are all 8-bit data word width and are all accessible through SMBus by read and write operations. ______________________________________________________________________________________ 11 Temperature Monitor with Dual Serial Interface MAX6638 Table 3. SMBus1 Registers and Command-Byte Bit Assignments REG. ADDRESS 00h 01h 02h 03h 04h 05h 06h 07h 08h 09h 0Ah 0Bh 0Ch 0Dh 0Eh 0Fh 10h 11h 19h 20h 21h 22h FEh FFh REGISTER NAME Read Local Temp Sensor Read Remote Temp Sensor Read Status Byte Read Configuration Byte Read Conversion-Rate Byte Read Local ALERT1 High Limit Read Local ALERT1 Low Limit Read Remote ALERT1 High Limit Read Remote ALERT1 Low Limit Write Configuration Byte Write Conversion-Rate Byte Write Local Alert-High Limit Write Local Alert-Low Limit Write Remote Alert-High Limit Write Remote Alert-Low Limit One-Shot Conversion Read Local-Extended Temp Read Remote-Extended Temp Read/Write Remote OVERT1 Limit Read/Write Local OVERT1 Limit Overtemperature Hysteresis Write Fault Queue Read Manufacturer ID Read Device ID ABBR. RLTS1 RRTS1 RS1 RC1 RCR1 RLAH1 RLAL1 RRAH1 RRAL1 WC1 WCR1 WLAH1 WLAL1 WRAH1 WRAL1 OSC1 RLET1 RRET1 RWRO1 RWLO1 HYS1 WFQ1 RMID RDID BIT 7 7 7 BUSY MASK 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 6 6 6 LHIGH RUN 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 5 5 5 LLOW RFU 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 4 4 4 RHIGH RFU 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 3 3 3 RFU 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 2 2 2 RFU 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 1 1 1 EOT RFU 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 IOT RFU 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 POR VALUE 00h 00h 00h 00h 00h 55h 00h 55h 00h 00h 08h 55h 00h 5Fh 00 -- 00h 00h 7Dh 55h 0Ah 80h 4Dh 78h RLOW FAULT 12 ______________________________________________________________________________________ Temperature Monitor with Dual Serial Interface MAX6638 Table 4. Read Status-Byte (RS1) Bit Assignments (02h) BIT 7 6 5 4 3 2 1 0 NAME BUSY LHIGH LLOW RHIGH RLOW OPEN EOT IOT POR STATE 0 0 0 0 0 0 0 0 ADC is busy converting when 1. Local High-Temperature Alarm. A 1 indicates a local high-temperature fault. Clears with a POR or readout of the status byte if the fault condition no longer exists. Local Low-Temperature Alarm. A 1 indicates a local low-temperature fault. Clears with a POR or readout of the status byte if the fault condition no longer exists. Remote High-Temperature Alarm. A 1 indicates a remote high-temperature fault. Clears with a POR or readout of the status byte if the fault condition no longer exists. Remote Low-Temperature Alarm. A 1 indicates a remote low-temperature fault. Clears with a POR or readout of the status byte if the fault condition no longer exists. A 1 indicates DXN and DXP are open. Clears with a POR or readout of the status byte if the open condition no longer exists. A 1 indicates the remote temperature exceeds the external OVERT1 threshold. A 1 indicates the local temperature exceeds the external OVERT1 threshold. FUNCTION Table 5. Read Configuration-Byte (RC1) Bit Assignments (03h) BIT 7 6 5-0 NAME MASK RUN RFU POR STATE 0 0 0 Masks ALERT1 interrupts when set to 1. Standby-Mode Control Bit. If set to 1, standby mode enables and enters if the standby-mode control bit (RUN) for channel 2 is also set. Reserved for future use. FUNCTION Table 6. Conversion-Rate Control-Byte (RCR1 and WCR1) Bit Assignments (04h and 0Ah) BIT 7-0 7-0 7-0 7-0 7-0 7-0 7-0 7-0 7-0 7-0 DATA 00h 01h 02h 03h 04h 05h 06h 07h 08h 09-FFh CONVERSION RATE (Hz) 0.0625 0.125 0.25 0.5 1 2 4 8 16 Reserved ______________________________________________________________________________________ 13 Temperature Monitor with Dual Serial Interface MAX6638 Table 7. SMBus2 Registers and Command-Byte Bit Assignments REG. ADDRESS 00h 01h 02h 03h 04h 05h 06h 07h 08h 09h 0Ah 0Bh 0Ch 0Dh 0Eh 0Fh 10h 11h 19h 20h 21h 22h FEh FFh REGISTER NAME Read Local Temp Sensor Read Remote Temp Sensor Read Status Byte Read Configuration Byte Read Conversion-Rate Byte Read Local ALERT1 High Limit Read Local ALERT1 Low Limit Read Remote ALERT1 High Limit Read Remote ALERT1 Low Limit Write Configuration Byte Write Conversion Rate Byte Write Local Alert-High Limit Write Local Alert-Low Limit Write Remote Alert-High Limit Write Remote Alert-Low Limit One-Shot Conversion Read Local-Extended Temp Read Remote-Extended Temp Read/Write Remote OVERT1 Limit Read/Write Local OVERT1 Limit Overtemperature Hysteresis Write Fault Queue Read Manufacturer ID Read Device ID ABBR. RLTS2 RRTS2 RS2 RC2 RCR2 RLAH2 RLAL2 RRAH2 RRAL2 WC2 WCR2 WLAH2 WLAL2 WRAH2 WRAL2 OSC2 RLET2 RRET2 RWRO2 RWLO2 HYS2 WFQ2 RMID RDID BIT 7 7 7 BUSY MASK 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 6 6 6 LHIGH RUN 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 5 5 5 LLOW RFU 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 4 4 4 RHIGH RFU 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 3 3 3 RFU 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 2 2 2 RFU 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 1 1 1 RFU RFU 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 RFU RFU 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 POR VALUE 00h 00h 00h 00h 00h 55h 00h 5Fh 00h 00h 08h 55h 00h 5Fh 00h -- 00h 00h 7Dh 55h 0Ah 80h 4Dh 78h RLOW FAULT 14 ______________________________________________________________________________________ Temperature Monitor with Dual Serial Interface MAX6638 Table 8. Read Status-Byte (RS2) Bit Assignments (02h) BIT 7 6 5 4 3 2 1 0 NAME BUSY LHIGH LLOW RHIGH RLOW OPEN RFU RFU POR STATE 0 0 0 0 0 0 0 0 ADC is busy converting when 1. Local High-Temperature Alarm. A 1 indicates a local high-temperature fault. Clears with a POR or readout of the status byte if the fault condition no longer exists. Local Low-Temperature Alarm. A 1 indicates a local low-temperature fault. Clears with a POR or readout of the status byte if the fault condition no longer exists. Remote High-Temperature Alarm. A 1 indicates a remote high-temperature fault. Clears with a POR or readout of the status byte if the fault condition no longer exists. Remote Low-Temperature Alarm. A 1 indicates a remote low-temperature fault. Clears with a POR or readout of the status byte if the fault condition no longer exists. A 1 indicates DXN and DXP are open. Clears with a POR or a read of the status byte if the open condition no longer exists. Reserved for future use. Reserved for future use. FUNCTION Table 9. Read Configuration-Byte (RC2) Bit Assignments (03h) BIT 7 6 5-0 NAME MASK RUN RFU POR STATE 0 0 0 Masks ALERT2 interrupts when set to 1. Standby-Mode Control Bit. If set to 1, standby mode is enabled and is entered if or when the standby-mode control bit (RUN) for channel 1 is also set. Reserved for future use. FUNCTION Table 10. Conversion-Rate Control-Byte (RCR2 and WCR2) Bit Assignments (04h and 0Ah) BIT 7-0 7-0 7-0 7-0 7-0 7-0 7-0 7-0 7-0 7-0 DATA 00h 01h 02h 03h 04h 05h 06h 07h 08h 09-FFh CONVERSION RATE (Hz) 0.0625 0.125 0.25 0.5 1 2 4 8 16 Reserved Table 11. Slave Addresses PART MAX6638ATC SMBus CHANNEL 1 2 SLAVE ADDRESS 1001 101 1001 101 ______________________________________________________________________________________ 15 Temperature Monitor with Dual Serial Interface MAX6638 Applications Information Remote-Diode Selection The MAX6638 can directly measure the die temperature of CPUs and other ICs that have on-board temperature-sensing diodes (see the Typical Operating Circuit), or it 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 (which is actually a transistor). The MAX6638 is optimized for n = 1.008. 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. The following example uses the MAX6638 with a CPU that has an ideality factor of 1.002. If the diode has negligible series resistance, the measured data is related to the real temperature as follows: n 1.008 TACTUAL = TM NOMINAL = TM = TM (1.00599) n1 1.002 Assume that the diode measured has a 3 series resistance. The series resistance contributes an offset of: 3 x 0.453 C = 1.36C The effects of the ideality factor and series resistance are additive. If the diode has a 1.002 ideality factor and 3 series resistance the total offset can be calculated by adding error due to series resistance with error due to ideality factor: 1.36C - 2.12C = -0.77C for a diode temperature of +85C. In this example, the effects of series resistance and 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 12 lists examples of discrete transistors that are appropriate for use with the MAX6638. 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 10A, and the forward voltage at the lowest expected temperature must be less than 0.95V at 100A. Do not use large power transistors. Ensure that the base resistance is less than 100. Tight specifications for forward current gain (50 < < 150, for example) indicate that the manufacturer has good process controls and that the device has consistent VBE characteristics. For a real temperature of +85C (358.15K), the converted and quantized temperature data is +82.875C (356.03K), which is an error of -2.12C. Using the correction formula above, the corrected temperature data is +85.0C (358.16K). Table 12. Remote-Sensor Transistor Manufacturers MANUFACTURER Central Semiconductor (USA) Rohm Semiconductor (USA) Samsung (Korea) Siemens (Germany) Zetex (England) SST3906 KST3906-TF SMBT3906 FMMT3906CT-ND MODEL CMPT3906 Effect of Series Resistance Series resistance (RS) in a sense diode contributes additional errors. For nominal diode currents of 10A and 100A, the change in the measured voltage due to RS is: VM = RS (100A - 10A) = 90A x RS. A 1C corresponds to 198.6V, series resistance contributes a temperature offset of: V = 0.453 C V 198.6 90 16 Note: Discrete transistors must be diode connected (base shorted to collector). ADC Noise Filtering The ADC is an integrating type with inherently good noise rejection, especially of low-frequency signals, such as 60Hz/120Hz power-supply hum. Micropower operation places constraints on high-frequency noise rejection; ______________________________________________________________________________________ Temperature Monitor with Dual Serial Interface therefore, careful PC board layout and proper external noise filtering are required for high-accuracy remote measurements in electrically noisy environments. Filter high-frequency EMI at DXP and DXN with an external 2200pF capacitor. This value can be increased to approximately 3300pF (max), including cable capacitance. Capacitance > 3300pF introduces errors due to the rise time of the switched current source. Typically noise sources cause the ADC measurements to be higher than the actual temperature, approximately by +1C to +10C, depending on the frequency and amplitude. traces. Use wider traces when practical. 7) Add a 200 resistor in series with V CC for best noise filtering (see the 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. MAX6638 PC Board Layout Checklist * * * * * * * * Place the MAX6638 close to the remote-sense junction. Keep traces away from high voltages (+12V bus). Keep traces away from fast data buses and CRTs. Use recommended trace widths and spacings. Place a ground plane under the traces. Use guard traces flanking DXP and DXN and connecting to GND. Add a 47 resistor in series with VCC for best noise filtering (see the Typical Operating Circuit). Place the noise filter and a 0.1F V CC bypass capacitor close to the MAX6638. PC Board Layout Follow these guidelines to reduce the measurement error of the temperature sensor: 1) Place the MAX6638 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 a 30C 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 12V DC. Leakage currents from PC board contamination must be dealt with carefully since a 20M leakage path from DXP to ground causes approximately a 1C 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 3V/C, and takes approximately 200V of voltage error at DXP-DXN to cause a 1C 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 10-mil withstand spacing recommended in Figure 4 is not absolutely necessary, as it offers only a minor improvement in leakage and noise over narrow 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 1 of series resistance, the error is approximately 0.5C. 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 ______________________________________________________________________________________ 17 Temperature Monitor with Dual Serial Interface MAX6638 MAX6638, the device follows temperature changes on the PC board with little or no perceivable delay. When measuring the temperature of a CPU or another 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 ALERT1 output. For example, with VCC 5.5V, at a 16Hz conversion rate and with ALERT1 sinking 1mA, the typical power dissipation is: 5.5V x 800A + 0.4V x 1.0mA = 4.8mW J-A for the 16-pin, 4mm x 4mm TQFN package is 59.3C/W, so assuming no copper PC board heat sinking, the resulting temperature rise is: T = 4.8mW x 59.3C/W = +0.283C. Even under nearly worst-case conditions, it is difficult to introduce a significant self-heating error. Typical Operating Circuit 0.1F 3.3V 47 DXP DXN 2200pF VCC SDA1 SCK1 ALERT1 10k 10k 10k 10k 10k 10k 10k DATA FROM/TO P1 CLOCK FROM P1 INTERRUPT TO P1 TO FAN DRIVER OR SYSTEM SHUTDOWN DATA FROM/TO P2 CLOCK FROM P2 INTERRUPT TO P2 P MAX6638 OVERT1 SDA2 SCK2 GND ALERT2 Chip Information PROCESS: BiCMOS 18 ______________________________________________________________________________________ Temperature Monitor with Dual Serial Interface 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.) 24L QFN THIN.EPS MAX6638 PACKAGE OUTLINE, 12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm 21-0139 E 1 2 PACKAGE OUTLINE, 12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm 21-0139 E 2 2 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 (c) 2006 Maxim Integrated Products Springer Printed USA is a registered trademark of Maxim Integrated Products, Inc. |
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