MAX31725 ±0.5°C Local Temperature Sensor General Description The MAX31725 temperature sensor accurately measures temperature and provides an overtemperature alarm/ interrupt/shutdown output. The device converts the temperature measurements to digital form using a high-resolution, sigma-delta, analog-to-digital converter (ADC). Accuracy is Q0.5NC from -40NC to +105NC. Communication is through an I2C-compatible 2-wire serial interface. The I2C serial interface accepts standard write byte, read byte, send byte, and receive byte commands to read the temperature data and configure the behavior of the open-drain overtemperature shutdown output. The MAX31725 features three address select lines with a total of 32 available addresses. The 2.5V to 3.7V supply voltage range, low 600FA supply current, and a lockupprotected I2C-compatible interface make the sensor ideal for a wide range of applications, including PCs, electronic test equipment, and office electronics. The MAX31725 is available in an 8-pin TDFN package and operates over the -55NC to +150NC temperature range. Applications Servers Telecom Networking Industrial Benefits and Features S±0.5NC Accuracy from -40NC to +105NC S16-Bit (0.00390625NC) Temperature Resolution SSelectable Timeout Prevents Bus Lockup (Default Enabled) S2.5V to 3.7V Supply Voltage Range S925µA (max) Operating Supply Current SSeparate Open-Drain OS Output Operates as Interrupt or Comparator/Thermostat Output Typical Application Circuit +2.5V TO +3.7V 4.7kΩ TO I2C MASTER VDD SDA SCL MAX31725 0.1µF A0 OS A1 GND A2 Ordering Information appears at end of data sheet. For related parts and recommended products to use with this part, refer to: www.maximintegrated.com/MAX31725.related For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com. 19-6477; Rev 0; 9/12 MAX31725 ±0.5°C Local Temperature Sensor ABSOLUTE MAXIMUM RATINGS (All voltages relative to GND.) Voltage Range on VDD, SDA, SCL, A0, A1.............-0.3V to +4V Voltage Range on A2, OS......................... -0.3V to (VDD + 0.3V) Input Current at Any Pin .................................................... +5mA Package Input Current .................................................... +20mA Continuous Power Dissipation (TA = +70NC) TDFN (derate 24.4mW/NC above +70NC)................1951.2mW ESD Protection (All Pins, Human Body Model) (Note 1)..... Q4000V Operating Temperature Range......................... -55NC to +150NC Junction Temperature......................................................+150NC Storage Temperature Range............................. -65NC to +150NC Lead Temperature (soldering, 10s).................................+300NC Soldering Temperature (reflow) ......................................+260NC Note 1: Human Body Model, 100pF discharged through a 1.5kI resistor. 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. PACKAGE THERMAL CHARACTERISTICS (Note 2) TDFN Junction-to-Ambient Thermal Resistance (qJA)...........41°C/W Junction-to-Case Thermal Resistance (qJC)..................8°C/W Note 2: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer board. For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial. RECOMMENDED OPERATING CONDITIONS (TA = -55NC to +150NC, unless otherwise noted.) (Notes 3, 4) PARAMETER SYMBOL Operating Supply Voltage VDD Input High Voltage VIH Input Low Voltage VIL CONDITIONS MIN TYP MAX UNITS 2.5 3.3 3.7 V VDD x 0.7 V VDD x 0.3 V ELECTRICAL CHARACTERISTICS (VDD = 2.5V to 3.7V, TA = -55NC to +150NC, unless otherwise noted. Typical values are VDD = 3.3V, TA = +25NC.) (Note 3) PARAMETER SYMBOL Accuracy (Note 5) CONDITIONS MIN 2.5V P + VDD P 3.7V, -40NC P TA P +105NC -0.5 +0.5 2.5V P + VDD P 3.7V, -55NC P TA P +150NC -0.7 +0.7 Temperature Conversion Noise 16 Conversion Time 44 First Conversion Completed Data ready after POR IDD NC 16 Bits 50 ms 50 ms 600 925 2.5 3.5 I2C inactive, TA = +150NC 800 -40NC to +125NC UNITS NC I2C inactive, TA = -40NC to +125NC Shutdown mode, I2C inactive, TA = Shutdown mode, I2C inactive, TA = +150NC Maxim Integrated MAX 0.0625 Temperature Data Resolution Quiescent Supply Current TYP FA 4.2 2 MAX31725 ±0.5°C Local Temperature Sensor ELECTRICAL CHARACTERISTICS (continued) (VDD = 2.5V to 3.7V, TA = -55NC to +150NC, unless otherwise noted. Typical values are VDD = 3.3V, TA = +25NC.) (Note 3) PARAMETER SYMBOL CONDITIONS MIN OS Delay Depends on fault queue setting 1 TOS Default Temperature Factory default setting 80 THYST Default Temperature Factory default setting 75 TYP MAX UNITS 6 Conversions 80 80 NC 75 75 NC POR Voltage Threshold 2.26 V POR Hysteresis 130 mV Input-High Leakage Current IIH VIN = 3.3V (all digital inputs) 0.005 1 FA Input-Low Leakage Current IIL VIN = 0V (all digital inputs ) 0.005 1 FA 1 FA Input Capacitance All digital inputs Output-High Leakage Current VIN = 3.3V (SDA and OS) 5 pF OS Output Saturation Voltage IOUT = 4.0mA 0.8 V Output Low Voltage IOL = 3mA (SDA) 0.4 V I2C AC ELECTRICAL CHARACTERISTICS (VDD = 2.5V to 3.7V, TA = -55NC to +150NC, unless otherwise noted. Typical values are VDD = 3.3V, TA = +25NC.) (Notes 3, 6) (Figure 1) PARAMETER SYMBOL Serial Clock Frequency fSCL Bus Free Time Between STOP and START Conditions tBUF START Condition Hold Time tHD:STA STOP Condition Setup Time tSU:STO CONDITIONS (Note 7) 90% of SCL to 10% of SDA MIN TYP DC MAX UNITS 400 kHz 1.3 Fs 0.6 Fs 600 ns Clock Low Period tLOW 1.3 Fs Clock High Period tHIGH 0.6 Fs START Condition Setup Time tSU:STA 90% of SCL to 90% of SDA 100 ns Data Setup Time tSU:DAT 10% of SDA to 10% of SCL 100 ns (Note 8) 100 ns Data Out Hold Time Data In Hold Time tDH tHD:DAT 10% of SCL to 10% of SDA (Note 8) 0 0.9 Fs Maximum Receive SCL/SDA Rise Time tR (Note 9) 300 ns Minimum Receive SCL/SDA Rise Time tR (Note 9) 20 + 0.1CB ns Maximum Receive SCL/SDA Fall Time tF (Note 9) 300 ns Minimum Receive SCL/SDA Fall Time tF (Note 9) 20 + 0.1CB ns Transmit SDA Fall Time tF (Note 9) Maxim Integrated 20 + 0.1CB 250 ns 3 MAX31725 ±0.5°C Local Temperature Sensor I2C AC ELECTRICAL CHARACTERISTICS (continued) (VDD = 2.5V to 3.7V, TA = -55NC to +150NC, unless otherwise noted. Typical values are VDD = 3.3V, TA = +25NC.) (Notes 3, 6) (Figure 1) PARAMETER SYMBOL CONDITIONS MIN Pulse Width of Suppressed Spike tSP (Note 10) 0 SDA Time Low for Reset of Serial Interface tTIMEOUT (Note 7) 45 TYP 50 MAX UNITS 50 ns 55 ms Note 3: Limits are 100% production tested at TA = +25NC and/or TA = +85NC. Limits over the operating temperature range and relevant supply voltage range are guaranteed by design and characterization. Typical values are not guaranteed. Note 4: All voltages are referenced to ground. Currents entering the IC are specified positive. Note 5: These limits represent a 3-sigma distribution. Note 6: All timing specifications are guaranteed by design. Note 7: Holding the SDA line low for a time greater than tTIMEOUT causes the devices to reset SDA to the idle state of the serial bus communication (SDA released). Note 8: A master device must provide a hold time of at least 300ns for the SDA signal to bridge the undefined region of SCL’s falling edge. Note 9:CB = total capacitance of one bus line in pF. Tested with CB = 400pF. Note 10:Input filters on SDA and SCL suppress noise spikes less than 50ns. SDA tBUF tF tLOW tHD:STA tSP SCL tHD:STA tHIGH tR tHD:DAT STOP START tSU:STA tSU:STO tSU:DAT REPEATED START NOTE: TIMING IS REFERENCED TO VIL(MAX) AND VIH(MIN). Figure 1. I2C Timing Diagram Maxim Integrated 4 MAX31725 ±0.5°C Local Temperature Sensor Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) STATIC QUIESCENT SUPPLY CURRENT vs. TEMPERATURE 8 3.3VDD IDD (µA) 3.7VDD 900 600 6 4 300 2.5VDD 0 -20 -70 30 80 130 30 130 ACCURACY vs. TEMPERATURE (VDD = 2.5V) ACCURACY vs. TEMPERATURE (VDD = 3.3V) 0.8 ERROR (°C) MEAN ERROR 0 MAX31725 toc04 1.5 +3 SIGMA ERROR +3 SIGMA ERROR 0 -3 SIGMA ERROR -3 SIGMA ERROR -0.5 80 TEMPERATURE (°C) MAX31725 toc03 0.5 -20 -70 TEMPERATURE (°C) 1.0 MEAN ERROR -0.8 -1.5 -1.0 -55 -30 -5 20 45 70 TEMPERATURE (°C) Maxim Integrated 3.7VDD 3.3VDD 2 2.5VDD 0 ERROR (°C) MAX31725 toc02 1200 IDD (µA) 10 MAX31725 toc01 1500 STATIC QUIESCENT SUPPLY CURRENT vs. TEMPERATURE (SHUTDOWN MODE) 95 120 -55 -30 -5 20 45 70 95 120 145 170 TEMPERATURE (°C) 5 MAX31725 ±0.5°C Local Temperature Sensor Pin Configuration TOP VIEW VDD A0 A1 A2 8 7 6 5 MAX31725 EP + 1 2 3 4 SDA SCL OS GND TDFN (3mm x 3mm) Pin Description PIN NAME 1 SDA Serial-Data Input/Output Line. Open drain. Connect SDA to a pullup resistor. High impedance for supply voltages from 0 to 3.7V. 2 SCL Serial-Data Clock Input. Open drain. Connect SCL to a pullup resistor. High impedance for supply voltages from 0 to 3.7V. 3 OS Overtemperature Shutdown Output. Open drain. Connect OS to a pullup resistor. 4 GND 5 A2 I2C Slave Address Input. Connect A2 to GND or VDD to set the desired I2C bus address. Do not leave unconnected (Table 1). 6 A1 I2C Slave Address Input. Connect A1 to GND, VDD, SDA, or SCL to set the desired I2C bus address. Do not leave unconnected (Table 1). High impedance for supply voltages from 0 to 3.7V. 7 A0 I2C Slave Address Input. Connect A0 to GND, VDD, SDA, or SCL to set the desired I2C bus address. Do not leave unconnected (Table 1). High impedance for supply voltages from 0 to 3.7V. 8 VDD — EP Maxim Integrated FUNCTION Ground Positive Supply Voltage Input. Bypass to GND with a 0.1mF bypass capacitor. Exposed Pad (Bottom Side of Package). Connect EP to GND. 6 MAX31725 ±0.5°C Local Temperature Sensor Block Diagram DIGITAL LOGIC BLOCK MAX31725 OS ACTIVATE TOS REGISTER TEMP REGISTER DIGITAL COMPARATOR THYST REGISTER OS THERMOSTAT LOGIC N I2C BLOCK DATA POINTER MSB 0 0 0 0 0 0 COMPARE/ INTERRUPT BIT FAULT QUEUE BITS LSB D1 D0 OS POLARITY BIT DATA REGISTER BLOCK D1 D0 0 SDA 0 SERIAL LOGIC SCL MS BYTE MSB TEMP S 26 25 22 21 20 LSB 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 1 LSB ONE DATA FAULT FAULT OS COMPARATOR/ TIMEOUT SHUTDOWN QUEUE QUEUE CONFIG SHOT FORMAT POLARITY INTERRUPT 1 0 MS BYTE MSB A0 A1 23 LS BYTE MSB 0 ADDRESS DECODER 24 LSB MSB LSB MSB LS BYTE 3 2 LSB 1 0 THYST S 26 25 24 23 22 21 20 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 1 1 TOS S 26 25 24 23 22 21 20 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 A2 TEMPERATURE CORE BLOCK VDD VDD GND Maxim Integrated POR BLOCK ONE-SHOT BIT DIGITAL CONTROL SHUTDOWN BIT VOLTAGE REFERENCE 16-BIT Σ∆ ADC TEMPERATURE SENSOR 7 MAX31725 ±0.5°C Local Temperature Sensor Detailed Description The MAX31725 temperature sensor measures temperature and converts the data into digital form. An I2C-compatible two-wire serial interface allows access to conversion results. The device accepts standard I2C commands to read the data, set the overtemperature alarm (OS) trip thresholds, and configure other characteristics. While reading the temperature register, any changes in temperature are ignored until the read is completed. The temperature register is updated for the new temperature measurement upon completion of the read operation. OS Output, TOS and THYST Limits In comparator mode, the OS output behaves like a thermostat (Figure 2). The output asserts when the temperature rises above the limit set in the TOS register. The output deasserts when the temperature falls below the limit set in the THYST register. In comparator mode, the OS output can be used to turn on a cooling fan, initiate an emergency shutdown signal, or reduce system clock speed. In interrupt mode, exceeding TOS also asserts OS. OS remains asserted until a read operation is performed on any of the registers. Once OS has asserted due to TOS TEMPERATURE THYST INACTIVE OS OUTPUT (COMPARATOR MODE) OS SET ACTIVE LOW ACTIVE INACTIVE OS OUTPUT (INTERRUPT MODE) OS SET ACTIVE LOW ACTIVE READ OPERATION READ OPERATION READ OPERATION Figure 2. OS Output Temperature Response Diagram Maxim Integrated 8 MAX31725 ±0.5°C Local Temperature Sensor crossing above TOS and is then reset, it is asserted again only when the temperature drops below THYST. The output then remains asserted until it is reset by a read. It is then asserted again if the temperature rises above TOS, and so on. Putting the MAX31725 into shutdown mode also resets OS. I2C-Compatible Bus Interface A standard I2C-compatible 2-wire serial interface reads temperature data from the temperature registers and reads and writes control bits and alarm threshold data to and from the alarm and configuration registers. The MAX31725 responds to its own I2C slave address, which is selected using the A0, A1, and A2 pins. A0 and A1 can be connected to the supply voltage, ground, SDA, or SCL. A2 can be connected to supply voltage or ground to provide up to 32 unique addresses. Table 1 shows how the A0, A1, and A2 connections determine the slave address. Maxim Integrated Table 1. Slave Address Selection SLAVE A2 A1 A0 ADDRESS CONNECTION CONNECTION CONNECTION BYTE (hex) GND GND GND 90h GND GND VDD 92h GND GND SCL 82h GND GND SDA 80h GND VDD GND 94h GND VDD VDD 96h GND VDD SCL 86h GND VDD SDA 84h GND SCL GND B4h GND SCL VDD B6h GND SCL SCL A6h GND SCL SDA A4h GND SDA GND B0h GND SDA VDD B2h GND SDA SCL A2h GND SDA SDA A0h VDD GND GND 98h VDD GND VDD 9Ah VDD GND SCL 8Ah VDD GND SDA 88h VDD VDD GND 9Ch VDD VDD VDD 9Eh VDD VDD SCL 8Eh VDD VDD SDA 8Ch VDD SCL GND BCh VDD SCL VDD BEh VDD SCL SCL AEh VDD SCL SDA ACh VDD SDA GND B8h VDD SDA VDD BAh VDD SDA SCL AAh VDD SDA SDA A8h 9 MAX31725 ±0.5°C Local Temperature Sensor be written for each I2C transaction. All registers are read and write, except for the read-only temperature register. Internal Registers The device contains four registers, each of which consists of 2 bytes. The configuration register contains only 1 byte of actual data and, when read as a 2-byte register, repeats the same data for the second byte. During a 2-byte write to the configuration register the second byte written takes precedence. The device’s pointer register selects between the four data registers shown in Table 2. During reads and writes the pointer register auto increments after every 2 data bytes, but does not wrap from address 03h-00h. The pointer register must Write to the configuration register by writing the slave address byte, the pointer register byte to value 01h, and a data byte. The TOS and THYST registers require the slave address byte, pointer register byte, and 2 data bytes. If only 1 data byte is written, it is saved in bits D[15:8] of the respective register. If more than 2 data bytes are written, the pointer register auto increments and if pointing to a valid address, additional data writes to the next address. See Figure 3. Table 2. Register Functions and POR State POR STATE REGISTER NAME ADDRESS (Hex) Hex BINARY POR STATE (°C) READ/ WRITE Temperature 00 0000h 0000 0000 0000 0000 0 Read-only Configuration 01 00h 0000 0000 — R/W THYST 02 4B00h 0100 1011 0000 0000 75 R/W TOS 03 5000h 0101 0000 0000 0000 80 R/W 1 1 9 0 D5* START BY MASTER D4* D3* D2* 1 D1* R/W 0 9 0 0 ACK BY MAX31725 ADDRESS BYTE 0 0 0 D1 D0 1 D7 9 D6 ACK BY MAX31725 POINTER BYTE D5 D4 D3 D2 D1 D0 ACK BY MAX31725 CONFIGURATION BYTE STOP COND BY MASTER (a) CONFIGURATION REGISTER WRITE. 1 1 START BY MASTER 9 0 D5* D4* D3* ADDRESS BYTE *SEE TABLE 1. D2* D1* R/W 1 0 ACK BY MAX31725 9 0 0 0 0 POINTER BYTE 0 D1 D0 ACK BY MAX31725 1 D7 9 D6 D5 D4 D3 MOST SIGNIFICANT DATA BYTE D2 D1 D0 ACK BY MAX31725 1 D7 9 D6 D5 D4 D3 LEAST SIGNIFICANT DATA BYTE D2 D1 STOP COND BY MASTER D0 ACK BY MAX31725 (b) TOS AND THYST WRITE. Figure 3. I2C-Compatible Timing Diagram (Write) Maxim Integrated 10 MAX31725 ±0.5°C Local Temperature Sensor Perform a read operation by issuing the slave address byte (write), pointer byte, repeat START, another slave address byte (read), and then reading the data byte. After 2 data bytes the pointer register auto increments and, if pointing to a valid address, additional data can be read. See Figure 4. data format is 16 bits, two’s complement, and the register is read out in 2 bytes: an upper byte and a lower byte. Bits D[15:0] contains the temperature data, with the LSB representing 0.00390625NC and the MSB representing the sign bit; see Table 3. The MSB is transmitted first. In addition to the normal two’s complement temperature data format, the MAX31725 offers an optional extended data format that allows temperatures equal to or greater than +128NC to be read. In the extended format, selected Temperature Registers Temperature data is stored in the temperature, TOS set point, and THYST set point registers. The temperature 1 9 1 0 D5* START BY MASTER D4* D3* D2* 1 D1* R/W 0 9 0 0 ACK BY MAX31725 ADDRESS BYTE 0 0 0 D1 1 D0 1 ACK BY MAX31725 POINTER BYTE 9 0 D5* D4* D3* D2* D1* R/W D7 9 D6 D5 ACK BY MAX31725 ADDRESS BYTE REPEAT START BY MASTER 1 D4 D3 D2 D1 STOP COND BY MASTER D0 NO ACK BY MASTER DATA BYTE (a) TYPICAL POINTER SET FOLLOWED BY IMMEDIATE READ FROM CONFIGURATION REGISTER. 1 9 1 0 START BY MASTER D5* D4* D3* D2* 1 D1* R/W 0 9 0 0 ACK BY MAX31725 ADDRESS BYTE 1 0 9 0 D5* D4* D3* D2* 0 D1 D0 ACK BY MAX31725 POINTER BYTE 1 REPEAT START BY MASTER 0 1 D1* R/W D7 ACK BY MAX31725 ADDRESS BYTE 9 D6 D5 D4 D3 D2 D1 D0 1 D7 9 D6 ACK BY MASTER MOST SIGNIFICANT DATA BYTE D5 D4 D3 D2 D1 D0 NO ACK BY MASTER LEAST SIGNIFICANT DATA BYTE STOP COND BY MASTER (b) TYPICAL POINTER SET FOLLOWED BY IMMEDIATE READ FOR 2-BYTE REGISTER SUCH AS TEMPERATURE, TOS, AND THYST. *SEE TABLE 1. Figure 4. I2C-Compatible Timing Diagram (Read) Table 3. Temperature, THYST, and TOS Register Definition UPPER BYTE D15 D14 MSB S 64NC 26 LOWER BYTE D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 32NC 16NC 8NC 4NC 2NC 1NC 0.5NC 0.25NC 0.125NC 0.0625NC 0.03125NC 0.015625NC 0.0078125NC 0.00390625NC 25 24 23 22 21 20 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 Maxim Integrated 11 MAX31725 ±0.5°C Local Temperature Sensor by bit 5 of the configuration register, the measured temperature is the value in the temperature register plus 64NC, as shown in Table 4. Configuration Register The configuration register contains 8 bits of data and initiates single conversions (ONE-SHOT), enables bus timeout, controls shutdown, sets the fault queue, sets the data format, selects OS polarity, and determines whether the OS output functions in comparator or interrupt mode. See Table 5. Shutdown Set bit D0 to 1 to place the device in shutdown mode and reduce supply current to 3.5FA or less. If bit D0 is set to 1 when a temperature conversion is taking place, the device completes the conversion and then shuts down. In interrupt mode, entering shutdown resets the OS output. While in shutdown, the I2C interface remains active and all registers remain accessible to the master. Setting D0 to 0 takes the device out of shutdown and starts a new conversion. The results of this conversion are available to read after the max conversion time. COMPARATOR/INTERRUPT Mode Set bit D1, the COMPARATOR/INTERRUPT bit to 0 to operate OS in comparator mode. In comparator mode, OS is asserted when the temperature rises above the TOS value. OS is deasserted when the temperature drops below the THYST value. See Figure 2. Set bit D1 to 1 to operate OS in interrupt mode. In interrupt mode, exceeding TOS also asserts OS. OS remains asserted until a read operation is performed on any of the registers. Once OS has asserted due to crossing above TOS and is then reset, it is asserted again only when the temperature drops below THYST. The output then remains asserted until it is reset by a read. It is then asserted again if the temperature rises above TOS, and so on. Putting the MAX31725 into shutdown mode also resets OS. Note that if the mode is changed while OS is active, an OS reset may be required before it begins to behave normally. OS Polarity Set bit D2, the OS POLARITY bit, to 0 to force the OS output polarity to active low. Set bit D2 to 1 to set the OS output polarity to active high. OS is an open-drain output Table 4. Temperature Data Output Format NORMAL FORMAT TEMPERATURE (°C) EXTENDED FORMAT BINARY Hex BINARY Hex +150 0111 1111 1111 1111 7FFFh 0101 0110 0000 0000 5600h +128 0111 1111 1111 1111 7FFFh 0100 0000 0000 0000 4000h +127 0111 1111 0000 0000 7F00h 0011 1111 0000 0000 3F00h +125 0111 1101 0000 0000 7D00h 0011 1101 0000 0000 3D00h +64 0100 0000 0000 0000 4000h 0000 0000 0000 0000 0000h +25 0001 1001 0000 0000 1900h 1101 1001 0000 0000 D900h +0.5 0000 0000 1000 0000 0080h 1100 0000 1000 0000 C080h 0 0000 0000 0000 0000 0000h 1100 0000 0000 0000 C000h -0.5 1111 1111 1000 0000 FF80h 1011 1111 1000 0000 BF80h -25 1110 0111 0000 0000 E700h 1010 0111 0000 0000 A700h -55 1100 1001 0000 0000 C900h 1000 1001 0000 0000 8900h Table 5. Configuration Register Definition D7 ONE-SHOT Maxim Integrated D6 D5 D4 D3 D2 D1 D0 TIMEOUT DATA FORMAT FAULT QUEUE [1] FAULT QUEUE [0] OS POLARITY COMPARATOR/ INTERRUPT SHUTDOWN 12 MAX31725 ±0.5°C Local Temperature Sensor under all conditions and requires a pullup resistor to output a high voltage. See Figure 2. Fault Queue Bits D4 and D3, the fault queue bits, determine the number of faults necessary to trigger an OS condition. See Table 6. The number of faults set in the queue must occur consecutively to trip the OS output. The fault queue prevents OS false tripping in noisy environments. Data Format Bit D5 selects the temperature data format for the temperature, TOS, and THYST registers. When D5 is 0 (normal format), the data format is two’s complement with a range of -128NC to +127.99609375NC. Set D5 to 1 for extended temperature format. In extended format, the measured temperature equals the two’s complement value plus 64NC, thereby extending the upper temperature data range to 191.99609375NC and allowing temperatures as high as 150NC to be measured. See Table 4. Once set, the data format does not update until the completion of the following temperature conversion. After setting D5 to 1, new extended temperature data is guaranteed ready after a time equal to twice the max conversion time. TIMEOUT Enable Set D6 to 1 to disable bus timeout. Set D6 to 0 to reset the I2C-compatible interface when SDA is low for more than 50ms (nominal). One-Shot The ONE-SHOT function helps to reduce average supply current when continuous conversions are not necessary. Setting D7 to 1 while the device is in shutdown mode immediately begins a new temperature conversion. After the conversion has completed, the device returns to shutdown mode. D7 returns to 0 when the conversion completes. Writing 1 to D7 has no effect when the device is not in shutdown. Table 6. Configuration Register Fault Queue Bits FAULT QUEUE [1] BIT D4 FAULT QUEUE [0] BIT D3 NUMBER OF FAULTS 0 0 1 (POR state) 0 1 2 1 0 4 1 1 6 Maxim Integrated Power-On Reset Value The configuration register always powers up to a known state, as indicated in Table 2. These default POR values correspond to the following modes of operation: • Comparator mode • OS active low • 1 fault, fault queue • Normal data format • Timeout enabled Applications Information The MAX31725 measures the temperature of its own die. The thermal path between the die and the outside world determines the accuracy of temperature measurements. External temperature is conducted to the die primarily through the leads and the exposed pad. Because of this, the device most easily measures the PCB temperature. For ambient temperature measurements, mount the device on a PCB (or a section of the PCB) that is at ambient temperature. Temperature errors due to self-heating of the device die are minimal due to the low supply current. Digital Noise Issues The device features an integrated lowpass filter on the SCL and SDA digital lines to mitigate the effects of bus noise. Although this filtering makes communication robust in noisy environments, good layout practices are always recommended. Minimize noise coupling by keeping digital traces away from switching power supplies. Ensure that digital lines containing high-speed data cross at right angles to the SDA and SCL lines. Excessive noise coupling into the SDA and SCL lines on the device— specifically noise with amplitude greater than 400mVP-P (typical hysteresis), overshoot greater than 300mV above +VDD, and undershoot more than 300mV below GND— can prevent successful serial communication. Serial bus not-acknowledge is the most common symptom, causing unnecessary traffic on the bus. Care must be taken to ensure proper termination within a system with long PCB traces or multiple slaves on the bus. Resistance can be added in series with the SDA and SCL lines to further help filter noise and ringing. If it proves to be necessary, a 5kI resistor should be placed in series with the SCL line, placed as close as possible to the SCL pin. This 5kI resistor, with the 5pF to 10pF stray capacitance of the device provide a 6MHz to 12MHz lowpass filter, which is sufficient filtering in most cases. 13 MAX31725 ±0.5°C Local Temperature Sensor Ordering Information PART TEMP RANGE TIMEOUT ENABLED AT POR PINPACKAGE MAX31725MTA+ -55NC to +150NC Yes 8 TDFN-EP* +Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad. Maxim Integrated Package Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 8 TDFN-EP T833+2 21-0137 90-0059 14 MAX31725 ±0.5°C Local Temperature Sensor Revision History REVISION NUMBER REVISION DATE 0 9/12 DESCRIPTION Initial release PAGES CHANGED — 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. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000 © 2012 Maxim Integrated Products, Inc. 15 The Maxim logo and Maxim Integrated are trademarks of Maxim Integrated Products, Inc.