MIC281-2BM-6

MIC281 Micrel MIC281 Low-Cost IttyBitty™ Thermal Sensor IttyBitty® REV 11/04 General Description Features 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. • Remote temperature measurement using embedded thermal diodes or commodity transistors • Accurate remote sensing ±3°C max., 0°C to 100°C • 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 • IttyBitty™ SOT23-6 Package Typical Application Applications • • • • Desktop, server and notebook computers Set-top boxes Game consoles Appliances 3.3V 10k pull-ups 5 TO SERIAL BUS HOST 4 0.1µF MIC281 DATA CLK VDD T1 1 NC GND 2 3 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 Ordering Information Part Number Standard Marking Pb-FREE Marking MIC281-0BM6* TB00 MIC281-0YM6* TB00 MIC281-1BM6* TB01 MIC281-1YM6* TB01 MIC281-2BM6* TB02 MIC281-2YM6* TB02 MIC281-3BM6* TB03 MIC281-3YM6* TB03 MIC281-4BM6 MIC281-4YM6 TB05 MIC281-5BM6* TB05 MIC281-5YM6* TB05 MIC281-6BM6* TB06 MIC281-6YM6* TB06 MIC281-7BM6* TB07 MIC281-7YM6* TB07 TB04 * Contact Micrel regarding availability Slave Address Ambient Temp. Range Package 1001 000xb -55°C to +125°C SOT23-6 1001 001xb -55°C to +125°C SOT23-6 1001 010xb -55°C to +125°C SOT23-6 1001 011xb -55°C to +125°C SOT23-6 1001 100xb -55°C to +125°C SOT23-6 1001 101xb -55°C to +125°C SOT23-6 1001 110xb -55°C to +125°C SOT23-6 1001 111xb -55°C to +125°C SOT23-6 Pin Configuration VDD 1 6 NC GND 2 5 DATA T1 3 4 CLK SOT23-6 Pin Description MIC281 Pin Pin Name 1 VDD 2 GND 3 T1 Pin Description Analog Input: Power supply input to the IC. Ground return for all IC functions. Analog Input: Connection to remote diode junction. 4 CLK Digital Input: Serial bit clock input. 5 DATA Digital I/O: Open-drain. Serial data input/output. 6 NC No Connection: Must be left unconnected. 2 November 2004 MIC281 Micrel Absolute Maximum Ratings (Note 1) Operating Ratings (Note 2) 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 = 125°C ................................ 109mW Junction Temperature ................................................ 150°C Storage Temperature ................................ –65°C to +150°C ESD Ratings, Note 7 Human Body Model ................................................ 1.5kV Machine Model ........................................................ 200V Soldering (SOT23-6 Package) Vapor Phase (60s) ......................................... 220 +5/–0°C Infrared (15s) ................................................. 235 +5/–0°C Power Supply Voltage, VDD ......................... +3.0V to +3.6V Ambient Temperature Range (TA) .............. –40°C to +85°C Package Thermal Resistance (θJA) SOT-23-6 ........................................................... 230°C/W Electrical Characteristics For typical values, TA=25°C, VDD=3.3V unless otherwise noted. Bold values are for TMIN ≤ TA ≤ TMAX unless otherwise noted. Note 2 Symbol Parameter Condition Supply Current Min Typ Max Units T1 open; CLK=DATA=High; Normal Mode 0.23 0.4 mA Shutdown mode; T1 open; CLK = 100kHz; Note 5 9 µA Shutdown Mode; T1 open; CLK=DATA=High 6 µA Power Supply IDD tPOR Power-on reset time, Note 5 VPOR Power-on reset voltage VHYST Power-on reset hysteresis voltage Note 5 VDD > VPOR 200 All registers reset to default values; A/D conversions initiated 2.65 µs 2.95 300 V mV Temperature-to-Digital Converter Characteristics Accuracy, Notes 3, 5, 6 0°C ≤ TD ≤ 100°C; 0°C ≤ TA ≤ 85°C; 3.15V ≤ VDD ≤ 3.45V –40°C ≤ TD ≤ 125°C; 0°C ≤ TA ≤ 85°C; 3.15V ≤ VDD ≤ 3.45V tCONV Conversion time, Note 5 IF Current into External Diode T1 forced to 1.0V, high level Note 5 Low level ±1 ±3 °C ±2 ±5 °C 200 240 ms 192 400 µA Remote Temperature Input, T1 7 12 µA Serial Data I/O Pin, DATA VOL Low Output Voltage, Note 4 IOL = 3mA 0.3 V 0.5 V VIL Low Input Voltage 3.0V ≤ VDD ≤ 5.5V 0.8 V CIN Input Capacitance, Note 5 VIH High Input Voltage ILEAK Input Current November 2004 IOL = 6mA 3.0V ≤ VDD ≤ 5.5V 2.1 5.5 10 ±1 3 V pF µA MIC281 MIC281 Symbol Micrel Parameter Condition Min Typ Max Units 0.8 V Serial Clock Input, CLK VIL Low Input Voltage 3.0V ≤ VDD ≤ 3.6V CIN Input Capacitance, Note 5 VIH High Input Voltage ILEAK Input current t1 t3 Data Out Stable After CLK Low 2.1 3.0V ≤ VDD ≤ 3.6V 5.5 10 V pF ±1 µA Serial Interface Timing CLK (clock) period 2.5 µs t2 Data in Setup Time to CLK High 100 ns t4 DATA Low Setup Time to CLK Low tTO t5 300 ns Start Condition 100 ns DATA High Hold Time After CLK High Stop Condition 100 Bus timeout 25 ns 30 35 ms Note 1. The device is not guaranteed to function outside its operating range. Note 2. Final test on outgoing product is performed at TA = 25°C. 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 t4 t5 t2 t3 SDA DATA OUTPUT Serial Interface Timing MIC281 4 November 2004 MIC281 Micrel Typical Characteristics VDD = 3.3V; TA = 25°C, unless otherwise noted. 350 1 300 0.5 0 -0.5 -1 -1.5 250 200 150 100 50 Quies c ent C urrent vs . T emperature in S hutdown Mode Quies c ent C urrent vs . S upply V oltage in S hutdown Mode 20 15 10 5 0 -55 -35 -15 5 25 45 65 85 105 125 TEMPERATURE (°C) R emote T emperature E rror vs . C apac itanc e on T 1 5 -10 -15 8000 7000 6000 5000 4000 3000 2000 1000 -20 3 0 1 400 10mV P -P 3mV P -P 10 100 1k 10k 100k 1M 10M100M FREQUENCY (Hz) 4 2 G ND 0 -2 3.3V -4 -6 1x10 9 E rror Due to Nois e on the C ollec tor of R emote T rans is tor 1.6 1.4 25mV P -P 4 1 100 200 300 FREQUENCY (kHz) -8 1x10 6 1x10 7 1x10 8 RESISTANCE FROM T1 (Ω) 3.6 5 2 0 6 TEMPERTURE ERROR (°C) REMOTE TEMP. ERROR (°C) -5 5 8 E rror Due to Nois e on the B as e of R emote T rans is tor 6 10 Meas urement E rror vs . P C B L eakage to +3.3V /G ND 7 0 0 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) 15 0 MEASUREMENT ERROR (°C) QUIESCENT CURRENT (µA) QUIESCENT CURRENT (µA) T 1 open DAT A = HIG H 0 -55 -35 -15 5 25 45 65 85 105 125 TEMPERATURE (°C) T 1 open 25 C LK = DAT A = HIG H TEMPERATURE ERROR (°C) 20 -2 100 0 20 40 60 80 REMOTE DIODE TEMPERATURE (°C) 30 Quies c ent C urrent vs . C loc k F requenc y in S hutdown Mode S upply C urrent vs . T emperature for V DD = 3.3V QUIESCENT CURRENT (µA) 400 1.5 SUPPLY CURRENT (µA) MEASUREMENT ERROR (°C) 2 R emote T emperature Meas urement E rror 100mV P -P 1.2 1.0 0.8 0.6 0.4 50mV P -P 0.2 0 1 25mV P -P 10 100 1k 10k 100k 1M 10M100M FREQUENCY (Hz) CAPACITANCE (pF) November 2004 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 Command Byte MIC281 Slave Address DATA 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. 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 NOT ACKNOWLEDGE ACKNOWLEDGE STOP CLK 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 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 R/W = WRITE START ACKNOWLEDGE ACKNOWLEDGE R/W = READ START ACKNOWLEDGE NOT ACKNOWLEDGE STOP CLK Master to slave transfer, i.e., DATA driven by master. Slave to master transfer, i.e., DATA driven by slave. Figure 2. Read_Byte Protocol Command Byte Value Target Register Label Description TEMP Remote temperature result CONFIG Configuration MFG_ID Manufacturer identification DEV_ID Device and revision identification Read Write 01h n/a 03h 03h FFh n/a FEh n/a Power-on Default 00h (0°C) 80h 2Ah 0xh* * The lower nibble contains the die revision level, e.g., Rev 0 = 00h. Table 1. MIC281 Register Addresses MIC281 6 November 2004 MIC281 Micrel 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 Slave Address MIC281-0BM6 1001 000xb = 90h MIC281-1BM6 MIC281-2BM6 MIC281-3BM6 MIC281-4BM6 MIC281-5BM6 MIC281-6BM6 MIC281-7BM6 Temperature 1001 001xb = 92h Hex +127°C 0111 1111 7F +125°C 0111 1101 7D +25°C 0001 1001 19 +1°C 0000 0001 01 0°C 0000 0000 00 –1°C 1111 1111 FF –25°C 1110 0111 E7 –125°C 1000 0011 83 –128°C 1000 0000 80 Table 3. Digital Temperature Format 1001 010xb = 94h 1001 011xb = 96h 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, +127°C. 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 100xb = 98h 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 Binary 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 Operation Measured temperature data for the remote zone Read-only Power-up default value: 0000 0000b = 00h (0°C)** Command byte: 0000 0001b = 01h Each LSB represents one degree centigrade. The values are in a two’s complement binary format such that 0°C 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 D[6] reserved Reserved Shutdown (SHDN) D[5] reserved D[4] reserved D[3] reserved D[2] reserved D[1] reserved D[0] write-only reserved Bits(s) Function Operation* D7 Reserved Always write as zero; reads undefined SHDN Shutdown bit 0 = normal operation, 1 = shutdown D[5:0] Reserved 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 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 0 0 1 0 1 0 1 0 BIT(S) FUNCTION Operation* D[7:0] Identifies Micrel as the manufacturer of the device. Always returns 2Ah. Read-only. Always returns 2Ah. Power-up default value: Read command byte: 0010 1010b = 2Ah 1111 1110b = FEh 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) Function Operation* D[7:0] Identifies the device revision number Read-only Power-up default value: Read command byte: November 2004 [Device revision number]h 1111 1111b = FFh 9 MIC281 MIC281 Micrel Application Information Series Resistance 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 0.9°C error in the MIC281’s temperature measurement. It is not difficult to keep the series resistance well below an ohm (typically < 0.1Ω), so this will rarely be an issue. 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 Part Number Package Fairchild Semiconductor MMBT3906 SOT-23 On Semiconductor MMBT3906L SOT-23 Infineon Technologies SMBT3906 SOT-23 Samsung Semiconductor KST3906-TF SOT-23 Table 4. Transistors Suitable for Use as Remote Diodes Filter Capacitor Selection 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. Minimizing Errors Self-Heating One concern when using a part with the temperature accuracy and resolution of the MIC281 is to avoid errors induced by self-heating (VDD × IDD) + (VOL × 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 × VDD)+(IOL(DATA) × VOL(DATA))] PD = [(0.4mA × 3.6V)+(6mA × 0.5V)] PD = 4.44mW Rθ(J-A) of SOT23-6 package is 230°C/W, therefore... the theoretical maximum self-heating is: 4.44mW × 230°C/W = 1.02°C Equation 1. Worst-Case Self-Heating PD = [(IDD × VDD)+(IOL(DATA) × VOL(DATA))] PD = [(0.23mA × 3.3V)+(25% × 1.5mA × 0.15V)] PD = 0.815mW Rθ(J-A) of SOT23-6 package is 230°C/W, therefore... the typical self-heating is: 0.815mW × 230°C/W = 0.188°C Equation 2. Real-World Self-Heating Example MIC281 10 November 2004 MIC281 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 0.1µF ceramic capacitor. Surface mount parts provide the best bypassing because of their low inductance. 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. MIC281 1 VDD NC 6 2 GND DATA 5 3 T1 CLK 4 GUARD/RETURN REMOTE DIODE (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) 1.30 (0.051) 0.90 (0.035) 3.00 (0.118) 2.80 (0.110) 0.20 (0.008) 0.09 (0.004) 10° 0° 0.50 (0.020) 0.35 (0.014) 0.15 (0.006) 0.00 (0.000) 0.60 (0.024) 0.10 (0.004) 6-Lead SOT23 (M6) MICREL INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com 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. © 2004 Micrel Incorporated MIC281 12 November 2004