Features MIC Channel SMBus Temperature Measurement System

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1 MIC284 Micrel, Inc. Two-Zone Termal Supervisor General Description Te MIC284 is a versatile digital termal supervisor capable of measuring temperature using its own internal sensor and an inexpensive external sensor or embedded silicon diode suc as tose found in te Intel Pentium III CPU. A 2-wire serial interface is provided to allow communication wit eiter I 2 C or SMBus masters. Features include an open-drain overtemperature output wit dedicated registers for implementing fan control or over-temperature sutdown circuits. Interrupt status and mask bits are provided for reduced software overead. Te open-drain interrupt output pin can be used as eiter an overtemperature alarm or a termostatic control signal. A programmable address pin permits two devices to sare te bus. (Alternate base addresses available-contact Micrel.) Superior performance, low power and small size makes te MIC284 an excellent coice for te most demanding termal management applications. Te MIC284 is part of te SilentSense family of termal supervisors. Data seets and support documentation can be found on Micrel s web site at SilentSense Features Optimized for CPU Termal Supervision in Computing Applications Measures Local and Remote Temperature Sigma-Delta ADC for 8-Bit Temperature Results 2-Wire SMBus-compatible Interface Programmable Termostat Settings for bot Internal and External Zones Open-Drain Interrupt Output Pin Open-Drain Over Temperature Output Pin for Fan Control or Hardware Sutdown Interrupt Mask and Status Bits Low Power Sutdown Mode Failsafe response to diode faults 2.7V to 5.5V Power Supply Range 8-Lead SOIC and MSOP Packages Applications Desktop, Server and Notebook Computers Power Supplies Test and Measurement Equipment Wireless Systems Networking/Datacom Hardware Typical Application FROM SERIAL BUS HOST OVER-TEMP SHUTDOWN 3.3V 4 10k pull-ups MIC284 DATA VDD CLK T1 /INT A0 /CRIT GND 0.1F 2200pF REMOTE DIODE 2-Cannel SMBus Temperature Measurement System SMBus and Pentium III are trademarks of Intel Corporation. I 2 C is a trademark of Pilips Electronics, N.V. SilentSense is a trademark of Micrel, Inc. Micrel, Inc Fortune Drive San Jose, CA USA tel + 1 (408) fax + 1 (408) ttp:// September MIC284

2 Micrel, Inc Ordering Information Part Number Base Address (*) Junction Temp. Range Package Availability Standard Pb-Free MIC284-0BM MIC284-0YM x -55 C to +125 C 8-Lead SOIC MIC284-1BM MIC284-1YM x -55 C to +125 C 8-Lead SOIC Contact Factory MIC284-2BM MIC284-2YM x -55 C to +125 C 8-Lead SOIC Contact Factory MIC284-3BM MIC284-3YM x -55 C to +125 C 8-Lead SOIC Contact Factory MIC284-0BMM MIC284-0YMM x -55 C to +125 C 8-Lead MSOP MIC284-1BMM MIC284-1YMM x -55 C to +125 C 8-Lead MSOP Contact Factory MIC284-2BMM MIC284-2YMM x -55 C to +125 C 8-Lead MSOP Contact Factory MIC284-3BMM MIC284-3YMM x -55 C to +125 C 8-Lead MSOP Contact Factory * Te least-significant bit of te slave address is determined by te state of te A0 pin. Pin Configuration DATA 1 8 VDD CLK 2 7 A0 /INT 3 6 T1 GND 4 5 /CRIT Pin Description Pin Number Pin Name Pin Function 1 DATA Digital I/O: Open-drain. Serial data input/output. 2 CLK Digital Input: Te ost provides te serial bit clock on tis input. 3 /INT Digital Output: Open-drain. Interrupt or termostat output. 4 GND Ground: Power and signal return for all IC functions. 5 /CRIT Digital Output: Open-Drain. Over-temperature indication 6 T1 Analog Input: Connection to remote temperature sensor (diode junction) 7 A0 Digital Input: Slave address selection input. See Table 1. MIC284 Slave Address Settings. 8 VDD Analog Input: Power supply input to te IC. MIC284 2 September 2005

3 Absolute Maximum Ratings (Note 1) Power Supply Voltage, V DD V Voltage on Any Pin V to V DD +0.3V Current Into Any Pin... ±10 ma Power Dissipation, T A = +125 C... 30mW Junction Temperature C Storage Temperature C to +150 C ESD Ratings (Note 3) Human Body Model...TBD V Macine Model...TBD V Soldering Vapor Pase (60 sec.) C +5 0 C Infrared (15 sec.) C +5 0 C Micrel, Inc. Operating Ratings (Note 2) Power Supply Voltage, V DD V to +5.5V Ambient Temperature Range (T A ) C to +125 C Package Termal Resistance (θ JA ) SOP C/W MSOP C/W Electrical Caracteristics 2.7V V DD 5.5; T A = +25 C, bold values indicate 55 C T A +125 C, Note 4; unless noted. Symbol Parameter Condition Min Typ Max Units Power Supply I DD Supply Current /INT, open, A0 = V DD or GND, µa CLK = DATA = ig, normal mode /INT, /CRIT open, A0 = V DD or GND sutdown mode, CLK = 100kHz 3 µa /INT, /CRIT open, A0 = V DD or GND sutdown mode, CLK = DATA = ig 1 10 µa t POR Power-On Reset Time, Note 7 V DD > V POR 200 µs V POR Power-On Reset Voltage all registers reset to default values, V A/D conversions initiated V HYST Power-On Reset Hysteresis Voltage 250 mv Temperature-to-Digital Converter Caracteristics Accuracy Local Temperature 0 C T A +100 C, /INT and /CRIT open, ±1 ±2 C Note 4, 9 3V V DD 3.6V 3V V DD 3.6V 55 C T A +125 C, /INT and /CRIT open, ±2 ±3 C Accuracy Remote Temperature 0 C T D +100 C, /INT and /CRIT open, ±1 ±3 C Note 4, 5, 9 3V V DD 3.6V, 0 C T A +85 C 3V V DD 3.6V, 0 C T A +85 C 55 C T D +125 C, /INT and /CRIT open, ±2 ±5 C t CONV0 Conversion Time, local zone ms Note 7 t CONV1 Conversion Time, remote zone Note ms Remote Temperature Input (T1) I F Current to External Diode ig level, T1 forced to 1.5V µa Note 7 low level µa Address Input (A0) V IL Low Input Voltage 2.7V V DD 5.5V 0.6 V V IH Hig Input Voltage 2.7V V DD 5.5V 2.0 V C IN Input Capacitance 10 pf I LEAK Input Current ±0.01 ±1 µa September MIC284

4 Micrel, Inc Symbol Parameter Condition Min Typ Max Units Serial Data I/O Pin (DATA) V OL Low Output Voltage I OL = 3mA 0.4 V Note 6 I OL = 6mA 0.8 V V IL Low Input Voltage 2.7V V DD 5.5V 0.3V DD V V IH Hig Input Voltage 2.7V V DD 5.5V 0.7V DD V C IN Input Capacitance 10 pf I LEAK Input current ±0.01 ±1 µa Serial Clock Input (CLK) V IL Low Input Voltage 2.7V V DD 5.5V 0.3V DD V V IH Hig Input Voltage 2.7V V DD 5.5V 0.7V DD V C IN Input Capacitance 10 pf I LEAK Input current ±0.01 ±1 µa Status Output (/INT) V OL Low Output Voltage, I OL = 3mA 0.4 V Note 6 I OL = 6mA 0.8 V t INT Interrupt Propagation Delay, from TEMP > T_SET or TEMPx < T_HYSTx t CONV +1 µs Note 7, 8 to INT < V OL, FQ = 00, R PULLUP = 10kΩ t nint Interrupt Reset Propagation Delay, from any register read to /INT > V OH 1 µs Note 7 FQ = 00, R PULLUP = 10kΩ T_SET0 Default T_SET0 Value t POR after V DD > V POR C T_HYST0 Default T_HYST0 Value t POR after V DD > V POR C T_SET1 Default T_SET1 Value t POR after V DD > V POR C T_HYST1 Default T_HYST1 Value t POR after V DD > V POR C Over-Temperature Output (/CRIT) V OL Low Output Voltage, I OL = 3mA 0.4 V Note 6 I OL = 6mA 0.8 V t CRIT /CRIT Propagation Delay, from TEMPx > T_SETx or TEMPx < T_HYSTx t CONV +1 µs Note 7, 8 to INT < V OL, FQ = 00, R PULLUP = 10kΩ t ncrit /CRIT Reset Propagation Delay, from TEMPx < ncritx to /CRIT > V OH 1 µs Note 7 FQ = 00, R PULLUP = 10kΩ CRIT1 Default CRIT1 Value t POR after V DD > V POR C ncrit1 Default ncrit1 Value t POR after V DD > V POR C Serial Interface Timing (Note 7) t 1 CLK (Clock) Period 2.5 µs t 2 Data In Setup Time to CLK Hig 100 ns t 3 Data Out Stable After CLK Low 0 ns t 4 DATA Low Setup Time to CLK Low start condition 100 ns t 5 DATA Hig Hold Time stop condition 100 ns After CLK Hig Note 1. Note 2. Note 3. Note 4. Exceeding te absolute maximum rating may damage te device. Te device is not guaranteed to function outside its operating rating. Devices are ESD sensitive. Handling precautions recommended. Human body model: 1.5k in series wit 100pF. Macine model: 200pF, no series resistance. Final test on outgoing product is performed at T A = TBD C. Note 5. T D is te temperature of te remote diode junction. Testing is performed using a single unit of one of te transistors listed in Table 6. Note 6. Note 7. Note 8. Note 9. Current into tis pin will result in self-eating of te MIC284. Sink current sould be minimized for best accuracy. Guaranteed by design over te operating temperature range. Not 100% production tested. t CONV = t CONV0 + t CONV1. t CONV0 is te conversion time for te local zone; t CONV1 is te conversion time for te remote zone.` Accuracy specification does not include quantization noise, wic may be as great as ±1 2LSB (±0.5 C). MIC284 4 September 2005

5 Timing Diagram SCL SDA Data In SDA Data Out t 4 t 1 t 2 t 5 t 3 Micrel, Inc. Serial Interface Timing September MIC284

6 Functional Diagram VDD Micrel, Inc TEMPERATURE-TO-DIGITAL CONVERTER T1 2:1 MUX Bandgap Sensor and Reference 1-Bit DAC Digital Filter and Control Logic Result Registers A0 DATA CLK 2-Wire Serial Bus Interface Pointer Register T_SET & /CRIT Setpoint Registers Temperature Hysteresis Registers Configuration Register State Macine and Digital Comparator Open-Drain Output /INT /CRIT MIC284 GND Functional Description Pin Descriptions VDD: Power supply input. See electrical specifications. GND: Ground return for all MIC284 functions. CLK: Clock input to te MIC284 from te two-wire serial bus. Te clock signal is provided by te ost, and is sared by all devices on te bus. DATA: Serial data I/O pin tat connects to te two-wire serial bus. DATA is bi-directional and as an open-drain output driver. An external pull-up resistor or current source somewere in te system is necessary on tis line. Tis line is sared by all devices on te bus. A0: Tis inputs sets te least significant bit of te MIC284 s 7-bit slave address. Te six most-significant bits are fixed and are determined by te part number ordered. (See ordering information table above.) Eac MIC284 will only respond to its own unique slave address, allowing up to eigt MIC284s to sare a single bus. A matc between te MIC284 s address and te address specified in te serial bit stream must be made to initiate communication. A0 sould be tied directly to VDD or ground. See "Temperature Measurement and Power On" for more information. A0 determines te slave address as sown in Table 1: P art Number Inputs MIC 284 S lave Addres s MIC284 6 September 2005 A0 B inary Hex MIC b b 49 MIC b 4A b 4B MIC b 4C b 4D MIC b 4E b 4F Table 1. MIC284 Slave Address Settings /INT: Temperature events are indicated to external circuitry via tis output. Operation of te /INT output is controlled by te MODE and IM bits in te MIC284 s configuration register. See "Comparator and Interrupt Modes" below. Tis output is open-drain and may be wire-or ed wit oter open-drain signals. Most systems will require a pull-up resistor or current source on tis pin. If te IM bit in te configuration register is set, it prevents te /INT output from sinking current. In I 2 C and SMBus systems, te IM bit is terefore an interrupt

7 mask bit. /CRIT: Over-temperature events are indicated to external circuitry via tis output. Tis output is open-drain and may be wire-or ed wit oter open-drain signals. Most systems will require a pull-up resistor or current source on tis pin. T1: Tis pin connects to an off-cip PN diode junction, for monitoring te junction temperature at a remote location. Te remote diode may be an embedded termal sensing junction in an integrated circuit so equipped (suc as Intel's Pentium III), or a discrete 2N3906-type bipolar transistor wit base and collector tied togeter. Temperature Measurement Te temperature-to-digital converter is built around a switced current source and an eigt-bit analog-to-digital converter. Eac diode's temperature is calculated by measuring its forward voltage drop at two different current levels. An internal multiplexer directs te MIC284's current source output to eiter an internal or external diode junction. Te MIC284 uses two scomplement data to represent temperatures. If te MSB of a temperature value is zero, te temperature is zero or positive. If te MSB is one, te temperature is negative. More detail on tis is given in te "Temperature Data Format" section below. A temperature event results if te value in eiter of te temperature result registers (TEMPx) becomes greater tan te value in te corresponding temperature setpoint register (T_SETx). Anoter temperature event occurs if and wen te measured temperature subsequently falls below te temperature ysteresis setting in T_HYSTx. During normal operation te MIC284 continuously performs temperature-to-digital conversions, compares te results against te setpoint registers, and updates te states of /INT, /CRIT, and te status bits accordingly. Te remote zone is converted first, followed by te local zone. Te states of /INT, /CRIT, and te status bits are updated after eac measurement is taken. Te remote diode junction connected to T1 may be embedded in an integrated circuit suc as a CPU, ASIC, or grapics processor, or it may be a diode-connected discrete transistor. Micrel, Inc. Diode Faults Te MIC284 is designed to respond in a failsafe manner to ardware faults in te external sensing circuitry. If te connection to te external diode is lost or te sense line (T1) is sorted to VDD or ground, te temperature data reported by te A/D converter will be forced to its full-scale value (+127 C). Tis will cause a temperature event to occur if T_SET1 or CRIT1 are set to any value less tan 127 C (7F = b ). An interrupt will be generated on /INT if so enabled. Te temperature reported for te external zone will remain +127 C until te fault condition is cleared. Tis fault detection mecanism requires tat te MIC284 complete te number of conversion cycles specified by Fault_Queue. Te part will terefore require one or more conversion cycles following power-on or a transition from sutdown to normal operation before reporting an external diode fault. Serial Port Operation Te MIC284 uses standard SMBus Write_Byte and Read_Byte operations for communication wit its ost. Te SMBus Write_Byte operation involves sending te device s slave address (wit te R/W bit low to signal a write operation), followed by a command byte and a data byte. Te SMBus Read_Byte operation is similar, but is a composite write and read operation: te ost first sends te device s slave address followed by te command byte, as in a write operation. A new start bit must ten be sent to te MIC284, followed by a repeat of te slave address wit te R/W bit (LSB) set to te ig (read) state. Te data to be read from te part may ten be clocked out. Te command byte is eigt bits wide. Tis byte carries te address of te MIC284 register to be operated upon, and is stored in te part s pointer register. Te pointer register is an internal write-only register. Te command byte (pointer register) values corresponding to te various MIC284 register addresses are sown in Table 2. Command byte values oter tan tose explicitly sown are reserved, and sould not be used. Any command byte sent to te MIC284 will persist in te pointer register indefinitely until it is overwritten by anoter command byte. If te location latced in te pointer register from te last operation is known to be correct (i.e., points to te desired register), ten te Receive_Byte procedure may be used. To perform a Receive_Byte, te ost sends an address byte to select te MIC284, and ten retrieves te data byte. Figures 1 troug 3 sow te formats for tese procedures. September MIC284

8 Micrel, Inc Command_Byte Binary He x Label b 00 TEMP b 01 CONFIG b 02 T_HYST b 03 T_SET b 10 TEMP b 12 T_HYST b 13 T_SET b 22 ncrit b 23 CRIT1 Target Registe r Descriptio n local temperature configuration registe r local temperature ysteresis local temperature setpoint remote temperature remote temperature ysteresis remote temperature setpoint over-temperature ysteresis over-temperature setpoin t Table 2. MIC284 Register Addresses MIC284 8 September 2005

9 Micrel, Inc. DATA CLK MIC284 Slave Address Command Byte Data Byte to MIC284 DATA S X X A0 0 A 0 0 X X X X X X A X X X X X X X X /A P START R/W = WRITE ACKNOWLEDGE ACKNOWLEDGE NOT ACKNOWLEDGE STOP CLK Figure 1. WRITE_BYTE Protocol MIC284 Slave Address Command Byte MIC284 Slave Address Data Read From MIC284 S X X A0 0 A 0 0 X X X X X X A S X X A0 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 Master-to-slave transmission Slave-to-master response Figure 2. READ_BYTE Protocol MIC284 Slave Address Data Byte from MIC284 DATA S X X A0 1 A X X X X X X X X /A P START R/W = READ ACKNOWLEDGE NOT ACKNOWLEDGE STOP CLK Master-to-slave transmission Slave-to-master response Figure 3. RECEIVE_BYTE September MIC284

10 Micrel, Inc t /INT INT MIC284 Slave Address First Byte of Transaction Last Byte of Transaction S X X X X A X X X X X X X X A X X X X X X X X /A P START R/W = DONT CARE ACKNOWLEDGE ACKNOWLEDGE Conversion in Progress Conversion Interrupted By MIC284 Acknowledge A/D Converter in Standby STOP NOT ACKNOWLEDGE New Conversion Begins Master-to-slave transmission Slave-to-master response New Conversion in Progress t CONV1 First Result Ready Figure 4. A/D Converter Timing MIC284 Slave Address Command Byte = 01 = CONFIG MIC284 Slave Address CONFIG Value* S X X A0 0 A A S X X A0 1 A X X X X X X X X /A P START R/W = WRITE ACKNOWLEDGE ACKNOWLEDGE START R/W = READ NOT ACKNOWLEDGE STOP ACKNOWLEDGE t n/int Temperature event occurs * Status bits in CONFIG are cleared to zero following tis operation Master-to-slave transmission Slave-to-master response Figure 5. Responding to Interrupts MIC September 2005

11 Temperature Data Format Te LSB of eac register represents one degree Centigrade. Te values are in a two s complement format, werein te most significant bit (D7), represents te sign: zero for positive temperatures and one for negative temperatures. Table 3 sows examples of te data format used by te MIC284 for temperatures. A/D Converter Timing Wenever te MIC284 is not in its low power sutdown mode, te internal A/D converter (ADC) attempts to make continuous conversions unless interrupted by a bus transaction accessing te MIC284. Wen te part is accessed, te conversion in progress will be alted, and te partial result discarded. Wen te access to te MIC284 is complete, te ADC will begin a new conversion cycle wit results for te remote zone valid t CONV1 after tat, and for te local zone t CONV0 later. Figure 4 sows tis beavior. Te conversion time is twice as long for external conversions as it is for internal conversions. Tis allows te use of a filter capacitor on T1 witout a loss of accuracy due to te resulting longer settling times. Upon powering-up, coming out of sutdown mode, or resuming operation following a serial bus transaction, te ADC will begin acquiring temperature data starting wit te external zone (zone 1), followed by te internal zone (zone 0). If te ADC is interrupted by a serial bus transaction, it will restart te conversion tat was interrupted and ten continue in te normal sequence. Tis sequence will repeat indefinitely until te MIC284 is sut down, powered off, or is interrupted by a serial bus transaction as described above. Power-On Wen power is initially applied, te MIC284 s internal registers are set to teir default states, and A0 is read to establis te device s slave address. Te MIC284 s power-up default state can be summarized as follows: Normal Mode operation (i.e., part is not in sutdown) /INT function is set to Comparator Mode Fault Queue dept = 1 (FQ=00) Interrupts are enabled (IM = 0) T_SET0 = 81 C; T_HYST0 = 76 C T_SET1 = 97 C; T_HYST1 = 92 C CRIT1 = 97 C; ncrit1 = 92 C Initialized to recognize overtemperature faults Comparator and Interrupt Modes Micrel, Inc. Depending on te setting of te MODE bit in te configuration register, te /INT output will beave eiter as an interrupt request signal or a termostatic control signal. Termostatic operation is known as comparator mode. Te /INT output is asserted wen te measured temperature, as reported in eiter of te TEMPx registers, exceeds te tresold programmed into te corresponding T_SETx register for te number of conversions specified by Fault_Queue (described below). In comparator mode, /INT will remain asserted and te status bits will remain ig unless and until te measured temperature falls below te value in te T_HYSTx register for Fault_Queue conversions. No action on te part of te ost is required for operation in comparator mode. Note tat entering sutdown mode will not affect te state of /INT wen te device is in comparator mode. In interrupt mode, once a temperature event as caused a status bit (Sx) to be set, and te /INT output to be asserted, tey will not be automatically de-asserted wen te measured temperature falls below T_HYSTx. Tey can only be de-asserted by reading any of te MIC284 s internal registers or by putting te device into sutdown mode. If te most recent temperature event was an overtemperature condition, Sx will not be set again, and /INT cannot be reasserted, until te device as detected tat TEMPx < T_HYSTx. Similarly, if te most recent temperature event was an undertemperature condition, Sx will not be set again, and /INT cannot be reasserted, until te device as detected tat TEMPx > T_SETx. Tis keeps te internal logic of te MIC284 backward compatible wit tat of te LM75 and similar devices. In bot modes, te MIC284 will be responsive to over-temperature events at power-up. See "Interrupt Generation", below. Sutdown Mode Setting te SHDN bit in te configuration register alts te oterwise continuous conversions by te A/D converter. Te MIC284 s power consumption drops to 1µA typical in sutdown mode. All registers may be read from or written to wile in sutdown mode. Serial bus activity will sligtly increase te part s power consumption. Entering sutdown mode will not affect te state of /INT wen te device is in comparator mode (MODE = 0). It will retain its state until after te device exits sutdown mode and resumes A/D conversions. If te device is sut down wile in interrupt mode (mode = Temperature Binary He x C b 7D + 25 C b C b 01 0 C b C b FF 25 C b E7 40 C b D8 55 C b C9 Table 3. Digital Temperature Format September MIC284

12 1), te /INT pin will be unconditionally de-asserted and te internal latces olding te interrupt status will be cleared. Terefore, no interrupts will be generated wile te MIC284 is in sutdown mode, and te interrupt status will not be retained. Regardless of te setting of te MODE bit, te state of /CRIT and its corresponding status bit, CRIT1, does not cange wen te MIC284 enters sutdown mode. Tey will retain teir states until after te device exits sutdown mode and resumes A/D conversions. Since entering sutdown mode stops A/D conversions, te MIC284 is incapable of detecting or reporting temperature events of any kind wile in sutdown. Diode fault detection requires one or more A/D conversion cycles to detect external sensor faults, terefore diode faults will not be reported until te MIC284 exits sutdown (see "Diode Faults" above). Fault Queues Fault queues (programmable digital filters) are provided in te MIC284 to prevent false tripping due to termal or electrical noise. Te two bits in CONFIG[4:3] set te dept of Fault_Queue. Fault_Queue ten determines te number of consecutive temperature events (TEMPx > T_SETx, TEMPx < T_HYSTx, TEMP1 > CRIT1, or TEMP1 < ncrit1) wic must occur in order for te condition to be considered valid. Tere are separate fault queues for eac zone and for te over-temperature detect function. As an example, assume te part is in comparator mode, and CONFIG[4:3] is programmed wit 10 b. Te measured temperature in zone one would ave to exceed T_SET1 for four consecutive A/D conversions before /INT would be asserted or te S1 status bit set. Similarly, TEMP1 would ave to be less tan T_HYST1 for four consecutive conversions before /INT would be reset. Like any filter, te fault queue function also as te effect of delaying te detection of temperature events. In tis example, it would take 4 x t CONV to detect a temperature event. Te dept of Fault_Queue vs. D[4:3] of te configuration register is sown in Table 4: CONFIG[4:3] Fault_Queue Dept 00 1 conversion* 01 2 conversions 10 4 conversions 11 6 conversions * Default setting Table 4. Fault_Queue Dept Settings Interrupt Generation Assuming te MIC284 is in interrupt mode and interrupts are enabled, tere are five different conditions tat will cause te MIC284 to set one of te status bits (S0, S1, or CRIT1) in CONFIG and assert its /INT output and/or /CRIT output. Tese conditions are listed in Table 5. Wen a temperature event occurs, te corresponding status bit will be set in CONFIG. Tis action cannot be masked. However, a temperature event will only generate an interrupt signal on /INT if it is specifically enabled by te interrupt mask bit (IM =0 in te configuration register). Following an interrupt, te ost sould read te contents of te configuration register to confirm tat te MIC284 was te source of te interrupt. Micrel, Inc A read operation on any register will cause /INT to be deasserted. Tis is sown in Figure 5. Te status bits will be cleared once CONFIG as been read. Since temperature-to-digital conversions continue wile /INT is asserted, te measured temperature could cange between te MIC284 s assertion of /INT or /CRIT and te ost s response. It is good practice for te interrupt service routine to read te value in TEMPx, to verify tat te overtemperature or under-temperature condition still exists. In addition, more tan one temperature event may ave occurred simultaneously or in rapid succession between te assertion of /INT and servicing of te MIC284 by te ost. Te interrupt service routine sould allow for tis eventuality. Keep in mind tat clearing te status bits and deasserting /INT is not sufficient to allow furter interrupts to occur. TEMPx must become less tan T_HYSTx if te last event was an over-temperature condition, or greater tan T_SETx if te last event was an under-temperature condition, before /INT can be asserted again. Putting te device into sutdown mode will de-assert /INT and clear te S0 and S1 status bits. Tis sould not be done before completing te appropriate interrupt service routine(s). /CRIT Output If and wen te measured remote temperature exceeds te value programmed into te CRIT1 register, te /CRIT output will be asserted and CRIT1 in te configuration register will be set. If and wen te measured temperature in zone one subsequently falls below te value programmed into ncrit1, te /CRIT output will be de-asserted and te CRIT1 bit in CONFIG will be cleared. Tis action cannot be masked and is completely independent of te settings of te mode bit and interrupt mask bit. Te ost may poll te state of te /CRIT output at any time by reading te configuration register. Te state of te CRIT1 bit exactly follows te state of te /CRIT output. Te states of /CRIT and CRIT1 do not cange wen te MIC284 enters sutdown mode. Entering sutdown mode stops A/D conversions, owever, so teir states will not cange wile te device is sut down. Polling Te MIC284 may eiter be polled by te ost, or request te ost s attention via te /INT pin. In te case of polled operation, te ost periodically reads te contents of CONFIG to ceck te state of te status bits. Te act of reading CON- FIG clears te status bits. If more tan one event tat sets a given status bit occurs before te ost polls te MIC284, only te fact tat at least one suc event as occurred will be apparent to te ost. For polled systems, te interrupt mask bit sould be set (IM = 1). Tis will disable interrupts from te MIC284, and prevent te /INT pin from sinking current. Te ost may poll te state of te /CRIT output at any time by reading te configuration register. Te state of te CRIT1 bit exactly follows te state of te /CRIT output. MIC September 2005

13 Micrel, Inc. E vent C ondition* * MIC284 response * ig temperature, remote TEMP1 > T_SET1 ig temperature, local TEMP0 > T_SET0 low temperature, remote TEMP1 > T_HYST1 low temperature, local TEMP0 > T_HYST0 over-temperatue, remote TEMP1 > CRIT1 NOT over-temperature, remote diode fault TEMP1 > ncrit1 T1 open or T1 sorted to VDD or GND * Assumes interrupts enabled ** Condition must be true for FAULT_QUEUE conversion to be recognized *** Assumes te T_SET1 and CRIT1 are set yo any value less ten +127 C = 7f = b Table 5. MIC284 Temperature Events set S1 in CONFIG, assert /INT set S0 in CONFIG, assert /INT set S1 in CONFIG, assert /INT set S0 in CONFIG, assert /INT set CRIT in CONFIG, assert /CRIT clear CRIT in CONFIG, de-assert /CRIT set CRIT and S1 in CONFIG, assert /INT and /CRIT*** September MIC284

14 Register Set and Programmer s Model Micrel, Inc Internal Register Set Name TEMP0 CONFIG T_HYST0 T_SET0 TEMP1 T_HYST1 T_SET1 ncrit1 CRIT1 Description Command Byte Operatio n Power-Up Default local temperature 00 8-bit read only 00 ( 0 C) (1) configuration registe r 01 8-bit 00 (2) local ysteresis 02 8-bit 4C (+76 C) local temperature setpoint 03 8-bit 51 (+81 C) remote temperature 10 8-bit read only 00 ( 0 C) (1) remote ysteresis 12 8-bit 5C (+92 C) remote temperature setpoint over-temperature ysteresis over-temperature temperature setpoint 13 8-bit 61 (+97 C) 22 8-bit 5C (+92 C) 23 8-bit 61 (+97 C) (1) TEMP0 and TEMP1 will contain measured temperature data after te completion of one conversion cycle. (2) After te first Fault_Queue conversions are complete, status bits will be set if TEMPx > T_SETx or TEMP1 > CRIT1. Detailed Register Descriptions Configuration Register read CONFIGURATION REGISTER (CONFIG) 8-Bit Read/Write D [7] D [6] D [5] D [4] D [3] D [2] D [1] D[0] only local status (S0) read only remote status (S1) read only /CRIT status (CRIT1) fault queue dept (FQ[1:0]) interrupt mask (IM) CMP/INT mode (MODE) Sutdown (SHDN) Bits Functio n S 0 local interrupt status (read only ) S 1 remote interrupt status (read only ) C RIT1 remote over-temperature status (read only ) FQ[1:0] IM MODE SHDN Fault_Queue dept interrupt mask comparator/interrupt mode selection for /INT pin normal/sutdown operating mode selection Operation 1 = event occured, 0 = no event 1 = event occured, 0 = no event 1 = over-temperature, 0 = no event 00 = 1 conversion, 01 = 2 conversions, 10 = 4 conversions, 11 = 6 conversions 1 = disabled, 0 = interrupts enabled 1 = interrupt mode, 0 = comparator mode 1 = sutdown, 0 = normal CONFIG Power-Up Value: b = 00 (*) not in sutdown mode comparator mode /INT = active low Fault_Queue dept = 1 interrupts enabled. no temperature events pending CONFIG Command Byte Value: b = 01 * Following te first Fault_Queue conversions, one or more of te status bits may be set. MIC September 2005

15 Micrel, Inc. Local Temperature Result Register LOCAL TEMPERATURE SETPOINT (T_SET0) 8-Bit Read/Write D [7] D [6] D [5] D [4] D [3] D [2] D [1] D[0] MSB bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 local temperature setpoint LSB Bits Functio n D [7:0] local temperature setpoint* Operation TEMP0 Power-Up Value: b = 00 (0 C) TEMP0 Command Byte Value: b = 00 * Eac LSB represents one degree Centigrade. Te values are in a two's complement format suc tat 0 C is reported as b. See "Temperature Data Format" for more details. TEMP0 will contain measured temperature data after te completion of one conversion. Local Temperature Hysteresis Register LOCAL TEMPERATURE HYSTERESIS (T_HYST0) 8-Bit Read/Write D [7] D [6] D [5] D [4] D [3] D [2] D [1] D[0] MSB bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 local temperature ysteresis setting LSB Bits Functio n D [7:0] local temperature ysteresis setting* Operation T_HYST0 Power-Up Value: b = 4C (+76 C) T_HYST0 Command Byte Value: b = 02 * Eac LSB represents one degree Centigrade. Te values are in a two's complement format suc tat 0 C is reported as b. See "Temperature Data Format" for more details. Local Temperature Setpoint Register LOCAL TEMPERATURE SETPOINT (T_SET0) 8-Bit Read/Write D [7] D [6] D [5] D [4] D [3] D [2] D [1] D[0] MSB bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 local temperature setpoint LSB Bits Functio n D [7:0] local temperature setpoint* Operation T_SET0 Power-Up Value: b = 51 (+81 C) T_SET0 Command Byte Value: b = 03 * Eac LSB represents one degree Centigrade. Te values are in a two's complement format suc tat 0 C is reported as b. See "Temperature Data Format" for more details. September MIC284

16 Micrel, Inc Remote Temperature Result Register REMOTE TEMPERATURE RESULT (TEMP1) 8-Bit Read Only D [7] D [6] D [5] D [4] D [3] D [2] D [1] D[0] MSB bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 remote temperature data from ADC* LSB Bits D[7:0] measured zone* Functio n temperature data for te remote read only Operation TEMP1 Power-Up Value: b = 00 (0 C) TEMP1 Command Byte Value: b = 10 * Eac LSB represents one degree Centigrade. Te values are in a two's complement format suc tat 0 C is reported as b. See "Temperature Data Format" for more details. TEMP1 will contain measured temperature data for te selected zone after te completion of one conversion. Remote Temperature Hysteresis Register REMOTE TEMPERATURE HYSTERESIS (T_HYST1) 8-Bit Read/Write D [7] D [6] D [5] D [4] D [3] D [2] D [1] D[0] MSB bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 remote temperature ysteresis setting LSB Bits Functio n D [7:0] remote temperature ysteresis setting* Operation T_HYST1 Power-Up Value: b = 5C (+92 C) T_HYST1 Command Byte Value: b = 12 * Eac LSB represents one degree Centigrade. Te values are in a two's complement format suc tat 0 C is reported as b. See "Temperature Data Format" for more details. Remote Temperature Setpoint Register REMOTE TEMPERATURE SETPOINT (T_SET1) 8-Bit Read/Write D [7] D [6] D [5] D [4] D [3] D [2] D [1] D[0] MSB bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 remote temperature setpoint LSB Bits Functio n D [7:0] remote temperature setpoint* Operation T_SET1 Power-Up Value: b = 61 (+97 C) T_SET1 Command Byte Value: b = 13 * Eac LSB represents one degree Centigrade. Te values are in a two's complement format suc tat 0 C is reported as b. See "Temperature Data Format" for more details. MIC September 2005

17 Micrel, Inc. Remote Over-Temperature Hysteresis Register REMOTE OVER-TEMPERATURE HYSTERESIS (ncrit1) 8-Bit Read/Write D [7] D [6] D [5] D [4] D [3] D [2] D [1] D[0] MSB bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 remote over-temperature ysteresis setting LSB Bits Functio n D [7:0] remote temperature ysteresis setting* Operation ncrit Power-Up Value: b = 5C (+92 C) ncrit1 Command Byte Value: b = 22 * Eac LSB represents one degree Centigrade. Te values are in a two's complement format suc tat 0 C is reported as b. See "Temperature Data Format" for more details. Remote Over-Temperature Setpoint Register REMOTE OVER-TEMPERATURE HYSTERESIS (ncrit1) 8-Bit Read/Write D [7] D [6] D [5] D [4] D [3] D [2] D [1] D[0] MSB bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 remote over-temperature ysteresis setting LSB Bits Functio n D [7:0] remote temperature ysteresis setting* Operation CRIT1 Power-Up Value: b = 61 (+97 C) CRIT1 Command Byte Value: b = 23 * Eac LSB represents one degree Centigrade. Te values are in a two's complement format suc tat 0 C is reported as b. See "Temperature Data Format" for more details. September MIC284

18 Applications Remote Diode Selection Most small-signal PNP transistors wit caracteristics similar to te JEDEC 2N3906 will perform well as remote temperature sensors. Table 6 lists several examples of suc parts tat Micrel as tested for use wit te MIC284. Oter transistors equivalent to tese sould also work well. Minimizing Errors Self-Heating One concern wen using a part wit te temperature accuracy and resolution of te MIC284 is to avoid errors induced by self-eating (V DD I DD ) + (V OL I OL ). In order to understand wat level of error tis migt represent, and ow to reduce tat error, te dissipation in te MIC284 must be calculated and its effects reduced to a temperature offset. Te worst-case operating condition for te MIC284 is wen V DD = 5.5V, MSOP-08 package. T e maximum power dissipated in te part is given in Equation 1 below. In most applications, te /INT output will be low for at most a few milliseconds before te ost resets it back to te ig state, making its duty cycle low enoug tat its contribution to self-eating of te MIC284 is negligible. Similarly, te DATA pin will in all likeliood ave a duty cycle of substantially below 25% in te low state. Tese considerations, combined wit more typical device and application parameters, give a better system-level view of device self-eating in interrupt-mode usage. Tis is illustrated by Equation 2. If te part is to be used in comparator mode, calculations similar to tose sown in Equation 2 (accounting for te expected value and duty cycle of I OL(/INT) and I OL(/CRIT) ) will give a good estimate of te device s self-eating error. In any application, te best test is to verify performance against calculation in te final application environment. Tis is especially true wen dealing wit systems for wic some Micrel, Inc of te termal data (e.g., PC board termal conductivity and ambient temperature) may be poorly defined or unobtainable except by empirical means. Series Resistance Te operation of te MIC284 depends upon sensing te ΔV CB-E of a diode-connected PNP transistor ( diode ) at two different current levels. For remote temperature measurements, tis is done using an external diode connected between T1 and ground. Since tis tecnique relies upon measuring te relatively small voltage difference resulting from two levels of current troug te external diode, any resistance in series wit te external diode will cause an error in te temperature reading from te MIC284. A good rule of tumb is tis: for eac om in series wit te external transistor, tere will be a 0.9 C error in te MIC284 s temperature measurement. It isn t difficult to keep te series resistance well below an om (typically < 0.1Ω), so tis will rarely be an issue. Filter Capacitor Selection It is sometimes desirable to use a filter capacitor between te T1 and GND pins of te MIC284. Te use of tis capacitor is recommended in environments wit a lot of ig frequency noise (suc as digital switcing noise), or if long wires are used to attac to te remote diode. Te maximum recommended total capacitance from te T1 pin to GND is 2700pF. Tis typically suggests te use of a 2200pF NP0 or C0G ceramic capacitor wit a 10% tolerance. If te remote diode is to be at a distance of more tan 6" 12" from te MIC284, using twisted pair wiring or sielded micropone cable for te connections to te diode can significantly elp reduce noise pickup. If using a long run of sielded cable, remember to subtract te cable s conductor-to-sield capacitance from te 2700pF maximum total capacitance. Layout Considerations Te following guidelines sould be kept in mind wen designing and laying out circuits using te MIC284: P D = [(I DD x V DD ) + (I OL(DATA) ) x V OL(DATA) + (I OL(/INT) x V OL(/INT) ) + (I OL(/CRIT) x V OL(/CRIT) )] P D = [(0.75mA x 5.5V) + (6mA x 0.8V) + (6mA x 0.8V) + (6mA x 0.8V)] P D = 18.53mW R θ(j-a) of MSOP - 08 package is 206 C/W Maximum T J relative to T A due to self eating is 18.53mW x 206 C/W = 3.82 C Equation 1. Worst-case self-eating [(0.35mA I DD(typ) x 3.3V) + (25% x 1.5mA I OL(DATA) ) x 0.3V) + (1% x 1.5mA I OL(/INT) x 0.3V) + (25% x 1.5mA I OL(/CRIT) x 0.3V) = 1.38mW T J = (1.38mW x 206 C/W) = 0.29 C Equation 2. Real-world self-eating example Vendor Part Number Package Faircild MMBT3906 SOT-23 On Semiconductor MMBT3906L SOT-23 Pillips Semiconductor PMBT3906 SOT-23 Samsung KST3906-TF SOT-23 Table 6. Transistors Suitable for Remote Temperature Sensing Use MIC September 2005

19 1. Place te MIC284 as close to te remote diode as possible, wile taking care to avoid severe noise sources suc as ig frequency power transformers, CRTs, memory and data busses, and te like. 2. Since any conductance from te various voltages on te PC Board and te T1 line can induce serious errors, it is good practice to guard te remote diode s emitter trace wit a pair of ground traces. Tese ground traces sould be returned to te MIC284 s own ground pin. Tey sould not be grounded at any oter part of teir run. However, it is igly desirable to use tese guard traces to carry te diode s own ground return back to te ground pin of te MIC284, tereby providing a Kelvin connection for te base of te diode. See Figure Wen using te MIC284 to sense te temperature of a processor or oter device wic as an integral termal diode, e.g., Intel s Pentium III, connect te emitter and base of te remote sensor to te MIC284 using te guard traces and Kelvin return sown in Figure 6. Te collector of te remote diode is typically inaccessible to te user on tese devices. To allow for tis, te MIC284 as superb rejection of noise appearing from collector to GND, as long as te base to ground connection is relatively quiet. 4. Due to te small currents involved in te measurement of te remote diode s ΔV BE, it is important to adequately clean te PC board after soldering to prevent current leakage. Tis is most likely to sow up as an issue in situations were water-soluble soldering fluxes are used. 5. In general, wider traces for te ground and T1 lines will elp reduce susceptibility to radiated noise (wider traces are less inductive). Use trace widts and spacing of 10 mils werever possible and provide a ground plane under te MIC284 and under te connections from te MIC284 to te remote diode. Tis will elp guard against stray noise pickup. Micrel, Inc. 6. Always place a good quality power supply bypass capacitor directly adjacent to, or underneat, te MIC284. Tis sould be a 0.1µF ceramic capacitor. Surface-mount parts provide te best bypassing because of teir low inductance. 7. Wen te MIC284 is being powered from particularly noisy power supplies, or from supplies wic may ave sudden ig-amplitude spikes appearing on tem, it can be elpful to add additional power supply filtering. Tis sould be implemented as a 100Ω resistor in series wit te part s VDD pin, and a 4.7µF, 6.3V electrolytic capacitor from VDD to GND. See Figure 7. MIC284 1 DATA VDD 8 2 CLK A0 7 GUARD/RETURN 3 4 /INT GND T1 /CRIT 6 5 REMOTE DIODE (T1) GUARD/RETURN Figure 6. Guard Traces/Kelvin Ground Returns 3.3V 100 FROM SERIAL BUS HOST OVER-TEMP SHUTDOWN 10k pull-ups MIC284 DATA VDD CLK T1 /INT A0 /CRIT GND 0.1F 4.7F 2200pF Remote Diode Figure 7. V DD Decoupling for Very Noisy Supplies September MIC284

20 Package Information Micrel, Inc 8-Lead SOIC (M) 8-Lead MSOP (MM) MICREL INC FORTUNE DRIVE SAN JOSE, CA USA TEL + 1 (408) FAX + 1 (408) WEB ttp:// Tis information furnised by Micrel reserves te rigt to cange circuitry and specifications at any time witout notification to te customer. Micrel Products are not reasonably be expected to result in personal injury. Life support devices or systems are devices or systems tat (a) are intended for surgical implant into te body or (b) support or sustain life, and wose failure to perform can be reasonably expected to result in a significant injury to te user. A Purcaser's use or sale of Micrel Pr Micrel for any damages resulting from suc use or sale Micrel Incorporated MIC September 2005