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| MIC281 Micrel MIC281 Low-Cost IttyBittyTM Thermal Sensor IttyBitty(R) REV 11/04 General Description The MIC281 is a digital thermal sensor capable of measuring the temperature of a remote PN junction. It is optimized for applications favoring low cost and small size. The remote junction may be an inexpensive commodity transistor, e.g., 2N3906, or an embedded thermal diode such as found in Intel Pentium* II/III/IV CPUs, AMD Athlon* CPUs, and Xilinx Virtex* FPGAs. The MIC281 is 100% software and hardware backward compatible with the MIC280 and features the same industry-leading noise performance and small size. The advanced integrating A/D converter and analog front-end reduce errors due to noise for maximum accuracy and minimum guardbanding. A 2-wire SMBus 2.0-compatible serial interface is provided for host communication. The clock and data pins are 5V-tolerant regardless of the value of VDD. They will not clamp the bus lines low even if the device is powered down. Superior performance, low power, and small size make the MIC281 an excellent choice for cost-sensitive thermal management applications. Features * Remote temperature measurement using embedded thermal diodes or commodity transistors * Accurate remote sensing 3C max., 0C to 100C * Excellent noise rejection * I2C and SMBus 2.0 compatible serial interface * SMBus timeout to prevent bus lockup * Voltage tolerant I/Os * Low power shutdown mode * Failsafe response to diode faults * 3.0V to 3.6V power supply range * IttyBittyTM SOT23-6 Package Applications * * * * Desktop, server and notebook computers Set-top boxes Game consoles Appliances Typical Application 3.3V 10k pull-ups 5 TO SERIAL BUS HOST 4 MIC281 DATA CLK NC VDD T1 GND 1 3 2 0.1F 2000pF CPU DIODE MIC281 Typical Application IttyBitty is a registered trademark of Micrel, Inc. *All trademarks are the property of their respective owners. Micrel, Inc. * 2180 Fortune Drive * San Jose, CA 95131 * USA * tel + 1 (408) 944-0800 * fax + 1 (408) 474-1000 * http://www.micrel.com November 2004 1 MIC281 MIC281 Micrel Part Number Slave Address Marking TB00 TB01 TB02 TB03 TB05 TB05 TB06 TB07 1001 000xb 1001 001xb 1001 010xb 1001 100xb 1001 101xb 1001 110xb 1001 111xb 1001 011xb -55C to +125C -55C to +125C -55C to +125C -55C to +125C -55C to +125C -55C to +125C -55C to +125C -55C to +125C SOT23-6 SOT23-6 SOT23-6 SOT23-6 SOT23-6 SOT23-6 SOT23-6 SOT23-6 Ambient Temp. Range Package Ordering Information Standard Marking Pb-FREE MIC281-0YM6* MIC281-1YM6* MIC281-2YM6* MIC281-3YM6* MIC281-4YM6 MIC281-5YM6* MIC281-6YM6* MIC281-7YM6* MIC281-0BM6* TB00 MIC281-1BM6* TB01 MIC281-2BM6* TB02 MIC281-3BM6* TB03 MIC281-4BM6 TB04 MIC281-5BM6* TB05 MIC281-6BM6* TB06 MIC281-7BM6* TB07 * Contact Micrel regarding availability Pin Configuration VDD 1 GND 2 T1 3 6 NC 5 DATA 4 CLK SOT23-6 Pin Description Pin 1 2 3 4 5 6 Pin Name VDD GND T1 CLK DATA NC Pin Description Analog Input: Power supply input to the IC. Ground return for all IC functions. Analog Input: Connection to remote diode junction. Digital Input: Serial bit clock input. Digital I/O: Open-drain. Serial data input/output. No Connection: Must be left unconnected. MIC281 2 November 2004 MIC281 Micrel Absolute Maximum Ratings (Note 1) Power Supply Voltage, VDD ..................................................... 3.8V Voltage on T1 ........................................ -0.3V to VDD+0.3V Voltage on CLK, DATA....................................-0.3V to 6.0V Current Into Any Pin ................................................. 10mA Power Dissipation, TA = 125C ................................ 109mW Junction Temperature ................................................ 150C Storage Temperature ................................ -65C to +150C ESD Ratings, Note 7 Human Body Model ................................................ 1.5kV Machine Model ........................................................ 200V Soldering (SOT23-6 Package) Vapor Phase (60s) ......................................... 220 +5/-0C Infrared (15s) ................................................. 235 +5/-0C Operating Ratings (Note 2) Power Supply Voltage, VDD ......................... +3.0V to +3.6V Ambient Temperature Range (TA) .............. -40C to +85C Package Thermal Resistance (JA) SOT-23-6 ........................................................... 230C/W Electrical Characteristics For typical values, TA=25C, VDD=3.3V unless otherwise noted. Bold values are for TMIN TA TMAX unless otherwise noted. Note 2 Symbol Parameter Condition Min Typ Max 0.4 Power Supply IDD Supply Current T1 open; CLK=DATA=High; Normal Mode Shutdown mode; T1 open; CLK = 100kHz; Note 5 Shutdown Mode; T1 open; CLK=DATA=High tPOR Power-on reset time, Note 5 Power-on reset voltage Power-on reset hysteresis voltage Note 5 Accuracy, Notes 3, 5, 6 0C TD 100C; 0C TA 85C; 3.15V VDD 3.45V VPOR VHYST VDD > VPOR All registers reset to default values; A/D conversions initiated 0.23 9 6 200 2.65 300 2.95 mA A A s V mV Units Temperature-to-Digital Converter Characteristics 1 2 200 192 7 12 0.3 0.5 0.8 2.1 10 1 5.5 3 5 240 400 C C ms A A V V V V pF A tCONV IF Conversion time, Note 5 Current into External Diode Note 5 Low Output Voltage, Note 4 Low Input Voltage High Input Voltage Input Capacitance, Note 5 Input Current -40C TD 125C; 0C TA 85C; 3.15V VDD 3.45V Remote Temperature Input, T1 T1 forced to 1.0V, high level Low level IOL = 3mA Serial Data I/O Pin, DATA VOL VIL IOL = 6mA VIH CIN 3.0V VDD 5.5V 3.0V VDD 5.5V ILEAK November 2004 3 MIC281 MIC281 Symbol VIL Parameter Low Input Voltage High Input Voltage Input Capacitance, Note 5 Input current CLK (clock) period Data in Setup Time to CLK High Data Out Stable After CLK Low DATA Low Setup Time to CLK Low Bus timeout Start Condition DATA High Hold Time After CLK High Stop Condition 2.5 100 300 100 100 25 30 35 Condition 3.0V VDD 3.6V 3.0V VDD 3.6V Min Typ Max 0.8 2.1 10 1 5.5 Serial Clock Input, CLK Micrel Units V V pF A s ns ns ns ns ms VIH CIN ILEAK t1 t2 t3 t4 t5 tTO Serial Interface Timing Note 1. The device is not guaranteed to function outside its operating range. Note 2. Final test on outgoing product is performed at TA = 25C. Note 3. TD is the temperature of the remote diode junction. Testing is performed using a single unit of one of the transistors listed in Table 5. Note 4. Current into the DATA pin will result in self-heating of the device. Sink current should be minimized for best accuracy. Note 5. Guaranteed by design over the operating temperature range. Not 100% production tested. Note 6. Accuracy specifications do not include quantization noise which may be up to 0.5LSB. Note 7. Devices are ESD sensitive. Observe appropriate handling precautions. Timing Diagram t1 SCL SDA DATA INPUT SDA DATA OUTPUT t4 t2 t3 t5 Serial Interface Timing MIC281 4 November 2004 MIC281 Micrel Typical Characteristics VDD = 3.3V; TA = 25C, unless otherwise noted. 2 1.5 MEASUREMENT ERROR (C) SUPPLY CURRENT (A) 1 0.5 0 -0.5 -1 -1.5 -2 100 0 20 40 60 80 REMOTE DIODE TEMPERATURE (C) R emote T emperature Meas urement E rror 400 350 S upply C urrent vs . T emperature for V DD = 3.3V 20 Quies c ent C urrent vs . C loc k F requenc y in S hutdown Mode T 1 open DAT A = HIG H QUIESCENT CURRENT (A) 300 250 200 150 100 50 0 -55 -35 -15 5 25 45 65 85 105 125 TEMPERATURE (C) 15 10 5 0 0 100 200 300 FREQUENCY (kHz) 400 Quies c ent C urrent vs . T emperature in S hutdown Mode 30 Quies c ent C urrent vs . S upply V oltage in S hutdown Mode 10 T 1 open 9 C LK = DAT A = HIG H 8 7 6 5 4 3 2 1 0 2.6 2.8 3.0 3.2 3.4 SUPPLY VOLTAGE (V) 8 6 MEASUREMENT ERROR (C) 4 2 0 -2 -4 -6 Meas urement E rror vs . P C B L eakage to +3.3V /G ND T 1 open 25 C LK = DAT A = HIG H QUIESCENT CURRENT (A) 20 15 10 5 0 -55 -35 -15 5 25 45 65 85 105 125 TEMPERATURE (C) QUIESCENT CURRENT (A) G ND 3.3V 3.6 -8 1x10 6 1x10 7 1x10 8 RESISTANCE FROM T1 () 1x10 9 R emote T emperature E rror vs . C apac itanc e on T 1 5 0 -5 -10 -15 -20 E rror Due to Nois e on the B as e of R emote T rans is tor 7 6 REMOTE TEMP. ERROR (C) 5 4 3 2 1 0 1 E rror Due to Nois e on the C ollec tor of R emote T rans is tor 1.6 1.4 TEMPERTURE ERROR (C) 1.2 1.0 0.8 0.6 0.4 0.2 0 1 25mV P -P 100mV P -P TEMPERATURE ERROR (C) 10mV P -P 3mV P -P 10 100 1k 10k 100k 1M 10M100M FREQUENCY (Hz) 50mV P -P 25mV P -P 10 100 1k 10k 100k 1M 10M100M FREQUENCY (Hz) 0 1000 2000 3000 4000 5000 6000 7000 CAPACITANCE (pF) November 2004 8000 5 MIC281 MIC281 Micrel Functional Description Serial Port Operation The MIC281 uses standard SMBus Write_Byte and Read_Byte operations for communication with its host. The SMBus Write_Byte operation involves sending the device's slave address (with the R/W bit low to signal a write operation), followed by a command byte and the data byte. The SMBus Read_Byte operation is a composite write and read operation: the host first sends the device's slave address followed by the command byte, as in a write operation. A new start bit must then be sent to the MIC281, followed by a repeat of the slave address with the R/W bit (LSB) set to the high (read) state. The data to be read from the part may then be clocked out. These protocols are shown in Figures 1 and 2. The Command byte is eight bits (one byte) wide. This byte carries the address of the MIC281 register to be operated upon. The command byte values corresponding to the various MIC281 registers are shown in Table 1. Other command byte values are reserved, and should not be used. MIC281 Slave Address DATA CLK Command Byte Data Byte to MIC281 S 1 0 0 1 A2 A1 A0 0 A X X X X X X X X A D7 D6 D5 D4 D3 D2 D1 D0 /A P START R/W = WRITE ACKNOWLEDGE ACKNOWLEDGE NOT ACKNOWLEDGE STOP Master to slave transfer, i.e., DATA driven by master. Slave to master transfer, i.e., DATA driven by slave. Figure 1. Write_Byte Protocol MIC281 Slave Address DATA CLK Master to slave transfer, i.e., DATA driven by master. Slave to master transfer, i.e., DATA driven by slave. Command Byte MIC281 Slave Address Data Read From MIC281 S 1 0 0 1 X X X 0 A X X X X X X X X A S 1 0 0 1 X X X 1 A X X X X X X X X /A P START R/W = WRITE ACKNOWLEDGE ACKNOWLEDGE START R/W = READ ACKNOWLEDGE NOT ACKNOWLEDGE STOP Figure 2. Read_Byte Protocol Target Register Label TEMP CONFIG MFG_ID DEV_ID Description Remote temperature result Configuration Manufacturer identification Device and revision identification Command Byte Value Read 01h FEh FFh 03h Write n/a 03h n/a n/a Power-on Default 00h (0C) 2Ah 80h 0xh* * The lower nibble contains the die revision level, e.g., Rev 0 = 00h. Table 1. MIC281 Register Addresses MIC281 6 November 2004 MIC281 Slave Address The MIC281 will only respond to its own unique slave address. A match between the MIC281's address and the address specified in the serial bit stream must be made to initiate communication. The MIC281's slave address is fixed at the time of manufacture. Eight different slave addresses are available as determined by the part number. See Table 2 below and the Ordering Information table. Part Number MIC281-0BM6 MIC281-1BM6 MIC281-2BM6 MIC281-3BM6 MIC281-4BM6 MIC281-5BM6 MIC281-6BM6 MIC281-7BM6 Slave Address 1001 000xb = 90h 1001 001xb = 92h 1001 010xb = 94h 1001 011xb = 96h 1001 100xb = 98h Temperature +127C +125C +25C +1C 0C -1C -25C -125C -128C Binary 0111 1111 0111 1101 0001 1001 0000 0001 0000 0000 1111 1111 1110 0111 1000 0011 1000 0000 Hex 7F 7D 19 01 00 FF E7 83 80 Micrel Table 3. Digital Temperature Format Diode Faults The MIC281 is designed to respond in a failsafe manner to diode faults. If an internal or external fault occurs in the temperature sensing circuitry, such as T1 being open or shorted to VDD or GND, the temperature result will be reported as the maximum full-scale value, +127C. Note that diode faults will not be detected until the first A/D conversion cycle is completed following power-up or exiting shutdown mode. Shutdown Mode Setting the shutdown bit in the configuration register will cause the MIC281 to cease operation. The A/D converter will stop and power consumption will drop to the ISHDN level. No registers will be affected by entering shutdown mode. The last temperature reading will persist in the TEMP register. 1001 101xb = 9Ah 1001 110xb = 9Ch 1001 111xb = 9Eh Table 2. MIC281 Slave Addresses Temperature Data Format The least-significant bit of the temperature register represents one degree Centigrade. The values are in a two's complement format, wherein the most significant bit (D7) represents the sign: zero for positive temperatures and one for negative temperatures. Table 3 shows examples of the data format used by the MIC281 for temperatures. November 2004 7 MIC281 MIC281 Micrel Detailed Register Descriptions Remote Temperature Result (TEMP) 8-bits, read-only Remote Temperature Result Register D[7] read-only D[6] read-only D[5] read-only D[4] read-only D[3] read-only D[2] read-only D[1] read-only D[0] read-only Temperature Data from ADC Bit D[7:0] Function Measured temperature data for the remote zone Operation Read-only Power-up default value: 0000 0000b = 00h (0C)** Command byte: 0000 0001b = 01h Each LSB represents one degree centigrade. The values are in a two's complement binary format such that 0C is reported as 0000 0000b. See Temperature Data Format (above) for more details. **TEMP will contain measured temperature data after the completion of one conversion. Configuration Register (CONFIG) 8-bits, read/write Configuration Register D[7] reserved Reserved D[6] reserved Shutdown (SHDN) Function Reserved Shutdown bit Reserved D[5] reserved D[4] reserved D[3] reserved reserved D[2] reserved D[1] reserved D[0] write-only Bits(s) D7 SHDN D[5:0] Operation* Always write as zero; reads undefined 0 = normal operation, 1 = shutdown Always write as zero; reads undefined Power-up default value: x0xx xxxxb (Not in shutdown mode) Command byte: 0000 0011b = 03h * Any write to CONFIG will result in any A/D conversion in progress being aborted and the result discarded. The A/D will begin a new conversion sequence once the write operation is complete. MIC281 8 November 2004 MIC281 Micrel Manufacturer ID Register (MFG_ID) 8-bits, read-only Manufacturer ID Register D[7] read-only 0 BIT(S) D[7:0] D[6] read-only 0 FUNCTION D[5] read-only 1 D[4] read-only 0 D[3] read-only 1 D[2] read-only 0 D[1] read-only 1 Operation* D[0] read-only 0 Power-up default value: Read command byte: Identifies Micrel as the manufacturer of the device. Always returns 2Ah. 0010 1010b = 2Ah 1111 1110b = FEh Read-only. Always returns 2Ah. Die Revision Register (DIE_REV) 8-bits, read-only Die Revision Register D[7] read-only D[6] read-only D[5] read-only D[4] read-only D[3] read-only D[2] read-only D[1] read-only D[0] read-only MIC281 DIE REVISION NUMBER Bit(s) D[7:0] Function Identifies the device revision number Operation* Read-only Power-up default value: Read command byte: [Device revision number]h 1111 1111b = FFh November 2004 9 MIC281 MIC281 Micrel Series Resistance Application Information Remote Diode Selection Most small-signal PNP transistors with characteristics similar to the JEDEC 2N3906 will perform well as remote temperature sensors. Table 4 lists several examples of such parts that Micrel has tested for use with the MIC281. Other transistors equivalent to these should also work well. Vendor Fairchild Semiconductor On Semiconductor Infineon Technologies Samsung Semiconductor Part Number MMBT3906 MMBT3906L SMBT3906 KST3906-TF Package SOT-23 SOT-23 SOT-23 SOT-23 Table 4. Transistors Suitable for Use as Remote Diodes Minimizing Errors Self-Heating The operation of the MIC281 depends upon sensing the VCB-E of a diode-connected PNP transistor ("diode ") at two different current levels. For remote temperature measurements, this is done using an external diode connected between T1 and ground. Since this technique relies upon measuring the relatively small voltage difference resulting from two levels of current through the external diode, any resistance in series with the external diode will cause an error in the temperature reading from the MIC281. A good rule of thumb is this: for each ohm in series with the external transistor, there will be a 0.9C error in the MIC281's temperature measurement. It is not difficult to keep the series resistance well below an ohm (typically < 0.1), so this will rarely be an issue. Filter Capacitor Selection One concern when using a part with the temperature accuracy and resolution of the MIC281 is to avoid errors induced by self-heating (VDD x IDD) + (VOL x IOL). In order to understand what level of error this might represent, and how to reduce that error, the dissipation in the MIC281 must be calculated and its effects reduced to a temperature offset. The worstcase operating condition for the MIC281 is when VDD = 3.6V. The maximum power dissipated in the part is given in Equation 1 below. In most applications, the DATA pin will have a duty cycle of substantially below 25% in the low state. These considerations, combined with more typical device and application parameters, give a better system-level view of device self-heating. This is illustrated by Equation 2. In any application, the best approach is to verify performance against calculation in the final application environment. This is especially true when dealing with systems for which some temperature data may be poorly defined or unobtainable except by empirical means. PD = [(IDD x VDD)+(IOL(DATA) x VOL(DATA))] PD = [(0.4mA x 3.6V)+(6mA x 0.5V)] PD = 4.44mW R(J-A) of SOT23-6 package is 230C/W, therefore... the theoretical maximum self-heating is: 4.44mW x 230C/W = 1.02C Equation 1. Worst-Case Self-Heating PD = [(IDD x VDD)+(IOL(DATA) x VOL(DATA))] PD = [(0.23mA x 3.3V)+(25% x 1.5mA x 0.15V)] PD = 0.815mW R(J-A) of SOT23-6 package is 230C/W, therefore... the typical self-heating is: 0.815mW x 230C/W = 0.188C Equation 2. Real-World Self-Heating Example It is usually desirable to employ a filter capacitor between the T1 and GND pins of the MIC281. The use of this capacitor is recommended in environments with a lot of high frequency noise (such as digital switching noise), or if long traces or wires are used to connect to the remote diode. The recommended total capacitance from the T1 pin to GND is 2200pF. If the remote diode is to be at a distance of more than 6"-12" from the MIC281, using twisted pair wiring or shielded microphone cable for the connections to the diode can significantly reduce noise pickup. If using a long run of shielded cable, remember to subtract the cable's conductor-to-shield capacitance from the 2200pF total capacitance. MIC281 10 November 2004 MIC281 Layout Considerations The following guidelines should be kept in mind when designing and laying out circuits using the MIC281: 1. Place the MIC281 as close to the remote diode as possible, while taking care to avoid severe noise sources such as high frequency power transformers, CRTs, memory and data busses, etc. 2. Since any conductance from the various voltages on the PC board and the T1 line can induce serious errors, it is good practice to guard the remote diode's emitter trace with a pair of ground traces. These ground traces should be returned to the MIC281's own ground pin. They should not be grounded at any other part of their run. However, it is highly desirable to use these guard traces to carry the diode's own ground return back to the ground pin of the MIC281, thereby providing a Kelvin connection for the base of the diode. See Figure 3. 3. When using the MIC281 to sense the temperature of a processor or other device which has an integral thermal diode, e.g., Intel's Pentium III, connect the emitter and base of the remote sensor to the MIC281 using the guard traces and Kelvin return shown in Figure 3. The collector of the remote diode is typically inaccessible to the user on these devices. Micrel 4. Due to the small currents involved in the measurement of the remote diode's VBE, it is important to adequately clean the PC board after soldering to prevent current leakage. This is most likely to show up as an issue in situations where water-soluble soldering fluxes are used. 5. In general, wider traces for the ground and T1 lines will help reduce susceptibility to radiated noise (wider traces are less inductive). Use trace widths and spacing of 10mm wherever possible and provide a ground plane under the MIC281 and under the connections from the MIC281 to the remote diode. This will help guard against stray noise pickup. 6. Always place a good quality power supply bypass capacitor directly adjacent to, or underneath, the MIC281. This should be a 0.1F ceramic capacitor. Surface mount parts provide the best bypassing because of their low inductance. MIC281 1 VDD 2 GND NC 6 DATA 5 CLK 4 GUARD/RETURN REMOTE DIODE (T1) 3 T1 GUARD/RETURN Figure 3. Guard Traces/Kelvin Ground Returns November 2004 11 MIC281 MIC281 Micrel Package Information 1.90 (0.075) REF 0.95 (0.037) REF 1.75 (0.069) 3.00 (0.118) 1.50 (0.059) 2.60 (0.102) DIMENSIONS: MM (INCH) 3.00 (0.118) 2.80 (0.110) 1.30 (0.051) 0.90 (0.035) 10 0 0.15 (0.006) 0.00 (0.000) 0.60 (0.024) 0.10 (0.004) 0.20 (0.008) 0.09 (0.004) 0.50 (0.020) 0.35 (0.014) 6-Lead SOT23 (M6) MICREL INC. TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser's use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser's own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. (c) 2004 Micrel Incorporated MIC281 12 November 2004 |
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