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may 2006 1 mic184 mic184 micrel mic184 local/remote thermal supervisor general description the mic184 is a versatile digital thermal supervisor capable of measuring temperature using either its own internal sensor or an inexpensive external sensor. a 2-wire serial interface is provided to allow communication with either i 2 c or smbus masters. this device is a pin-for-pin and software compatible upgrade for the industry standard lm75. additional features include remote temperature meas urement capability, and interrupt status and mask bits in the chips con?guration register for software polling. the open-drain interrupt output pin can be used as either an overtemperature alarm or thermostatic control signal. three program mable ad- dress pins permit users to multidrop up to 8 devices along the 2-wire bus, allowing simple distributed temperature sensing networks. superior performance, low power and small size makes the mic184 an excellent choice for the most demand- ing thermal management applications. typical application data 12 3 8 4 56 7 from serial bus host optionalremote temperature sensor 2200pf mic184 clkint data 3.0v to 3.6vv dd clock interrupt vdd 3 10k a2/t1 a1a0 gnd 0.1fceramic 2-channel smbus temperature measurement system features ? measures local and remote temperatures ? pin and software backward compatible to lm75 ? 9-bit sigma-delta adc ? 2-wire i 2 c/smbus compatible interface ? programmable thermostatic settings for either internal or external zone ? open-drain comparator/interrupt output pin ? interrupt mask and status bits ? low-power shutdown mode ? fail-safe response to diode faults ? 2.7v to 5.5v power supply range ? up to 8 devices may share the same bus ? 8-lead sop and msop packages applications ? desktop, server and notebook computers ? printers and copiers ? test and measurement equipment ? consumer electronics ordering information part number temperature range package pb-free mic184bm -55c to +125c 8-lead soic mic184bmm -55c to +125c 8-lead msop MIC184YM -55c to +125c 8-lead soic x MIC184YMm -55c to +125c 8-lead msop x micrel, inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel + 1 (408) 944-0800 ? fax + 1 (408 ) 474-1000 ? http://www.micrel.com downloaded from: http:///
mic184 micrel mic184 2 may 2006 pin description pin number pin name pin function 1 data data (digital i/o): open-drain. serial data input/output. 2 clk clock (digital input): the host provides the serial bit clock on this input. 3 int interrupt (digital output): open-drain. interrupt or thermostat output. 4 gnd ground: power and signal return for all ic functions. 5 a2/t1 address bit 2 (digital input): slave address selection input. see slave ad- dress truth table. temperature sensor 1 (analog input): input from remote temperature sensor (diode junction). 6 a1 address bit 1 (digital input): slave address selection input. see slave ad- dress truth table. 7 a0 address bit 0 (digital input): slave address selection input. see slave ad- dress truth table. 8 vdd supply (analog input): power supply input to the ic. pin con?guration 1 data clk int gnd 8 vdd a0a1 a2/t1 76 5 23 4 downloaded from: http:///
may 2006 3 mic184 mic184 micrel absolute maximum ratings (note 1) power supply voltage, v dd .......................................... 6.0v voltage on any pin ................................ C0.3v to v dd +0.3v current into any pin ................................................... 6ma power dissipation, t a = +125c ................................ 30mw junction temperature .............................................. +150c storage temperature ................................ C65c to +150c esd ratings (note 3) human body model ..................................................... 700v machine model ............................................................ 100v soldering vapor phase (60 sec.) .............................. +220c +5 ? C0 c infrared (15 sec.) ...................................... +235c +5 ? C0 c operating ratings (note 2) power supply voltage, v dd ......................... +2.7v to +5.5v ambient temperature range (t a ) ............. -55c to +125c package thermal resistance ( ja ) sop .................................................................+152c/w msop ..............................................................+206c/w electrical characteristics2.7v v dd 5.5; t a = +25c, bold values indicate C55c t a +125c, note 4 ; unless noted. symbol parameter condition min typ max units power supplyi dd supply current int open, a2, a1, a0 = v dd or gnd, 340 500 a clk = data = high, normal mode shutdown mode, clk = 100khz 2.5 a int open, a2, a1, a0 = v dd or gnd, 1 10 a clk = data = high, shutdown mode t por power-on reset time v dd > v por 15 100 s v por power-on reset voltage all registers reset to default values, 2.0 2.7 v a/d conversions initiated v hyst power-on reset hysteresis voltage 250 mv temperature-to-digital converter characteristics accuracylocal temperature 0c t a +100c, int open, 1 2 c note 5, 6 3v v dd 3.6v C55c t a +125c, int open, 2 3 c 3v v dd 3.6v accuracyremote temperature 0c t d +100c, int open, 1 3 c note 5, 6, 7 3v v dd 3.6v, 0c t a +85c C55c t d +125c, int open, 2 5 c 3v v dd 3.6v, 0c t a +85c t conv conversion time, note 5 local temperature 100 160 ms remote temperature 200 320 ms remote temperature input (t1) i f current to external diode high level 224 400 a note 5 low level 7.5 14 a address inputs (a2/t1, a1, a0) v il low input voltage 2.7v v dd 5.5v 0.6 v v ih high input voltage 2.7v v dd 5.5v 2.0 v c in input capacitance 10 pf i leak input current 0.01 1 a i pd pulldown current on a2/t1 a2 = v dd , ?ows for t por at power-up 25 a downloaded from: http:///
mic184 micrel mic184 4 may 2006 symbol parameter condition min typ max units serial data i/o pin (data) v ol low output voltage i ol = 3ma 0.4 v i ol = 6ma 0.8 v v il low input voltage 2.7v v dd 5.5v 0.3v dd v v ih high 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 a serial clock input (clk)v il low input voltage 2.7v v dd 5.5v 0.3v dd v v ih high 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 a status output (int)v ol low output voltage, i ol = 3ma 0.4 v note 8 i ol = 6ma 0.8 v t int interrupt propagation delay, from temp > t_set, fq = 00 to int < v ol , t conv +1 s note 5 r pullup = 10k; pol bit = 0 t nint interrupt reset propagation delay, from any register read to int > voh, 1 s note 5 r pullup = 10k; pol bit = 0 t_set default t_set value t por after v dd > v por , note 9 80 80 80 c hyst default hyst value t por after v dd > v por , note 9 75 75 75 c serial interface timing (note 5) t 1 clk (clock) period 2.5 s t 2 data in setup time to clk high 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 high hold time stop condition 100 ns after clk high note 1. exceeding the absolute maximum rating may damage the device. note 2. the device is not guaranteed to function outside its operating rating. note 3. devices are esd sensitive. handling precautions recommended. human body model: 1.5k in series with 100pf. machine model: 200pf, no series resistance. note 4. final test on outgoing product is performed at t a = tbdc. note 5. guaranteed by design over the operating temperature range. not 100% production tested. note 6. accuracy speci?cation does not include quantization noise, which may be as great as 1 ? 2 lsb ( 1 ? 4 c). note 7. t d 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 8. current into the int pin will result in self-heating of the mic184. int pin current should be minim ized for best accuracy. note 9. this is the decimal representation of a binary data value. timing diagram t 1 t 2 t 5 t 4 t 3 scl sda?input sda?output serial interface timing downloaded from: http:///
may 2006 5 mic184 mic184 micrel typical characteristics -3 -2 -1 0 1 2 3 -60-40 -20 0 2040 60 80 100120 140 mesurement?error ( c) local?diode?temerature ( c) l oc al t emperature meas urement e rror v dd = 3.3v -5 -4 -3 -2 -1 0 1 2 3 4 5 -60-40 -20 0 2040 60 80 100120 140 mesurement?error ( c) remote?diode?temerature ( c) r emote?t emperature meas urement e rror v dd = 3.3v 0 50 100 150 200 250 300 350 400 450 500 -60-40 -20 0 2040 60 80 100120 140 supply?current ( a) temperature ( c) operating i dd vs .?t emperature v dd = 3.3v v dd = 5.0v f c loc k = 0hz 0 1 2 3 4 5 6 7 8 9 0 50 100 150 200 250 300 350 400 shutdown?current ( a) clock?frequency?(khz) s hutdown i dd vs . f requenc y v dd = 3.0v v dd = 5.0v 0 0.5 1 1.5 2 2.5 3 3.5 -60-40 -20 0 2040 60 80 100120 140 shutdown?current ( a) temperature ( c) s hutdown mode i dd vs .?t emperature v dd = 5.0v v dd = 3.3v f c loc k = 0hz 0 50 100 150 200 250 300 350 400 0 2 4 6 supply?current ( a) supply?voltage?(v) s upply c urrent vs . s uppl y v oltage 0 20 40 60 80 100 120 140 0 5 10 15 measured?local?temperature ( c) time?(sec) r es pons e to?immers ion in 125 c f luid b ath s oic -8 ms op -8 -30 -25 -20 -15 -10 -5 0 5 1x10 6 1x10 7 1x10 8 1x10 9 measurement?error ( c) resistance?from?t1( ? ) meas urement e rror vs . p c b l eakage to +5v /+3.3v /g nd g nd 3.3v 5.0v -12 -10 -8 -6 -4 -2 0 0 1 2 3 4 5 6 7 8 9 10 measurment?error ( c) capacitance?(nf) meas urment e rror vs . c apc itanc e?on t 1 downloaded from: http:///
mic184 micrel mic184 6 may 2006 functional descriptionpin descriptions vdd power supply input. see electrical speci?cations. gnd ground return for all mic184 functions. clk clock input to the mic184 from the two-wire serial bus. the clock signal is provided by the bus host and is shared by all devices on the bus. data serial data i/o pin that connects to the two-wire serial bus. data is bidirectional and has an open-drain output driver. an external pull-up resistor or current source somewhere in the system is necessary on this line. this line is shared by all devices on the bus. a2/t1, a1, a0 these inputs set the three least signi?cant bits of the mic184s 7-bit slave address. each mic184 will only respond to its own unique slave address, allowing the use of up to eight mic184s on a single bus. a match between the mic184s address and functional diagram 2:1 mux temperature-to-digital converter 1-bit dac a2/t1 a1a0 data mic184 clk int 2-wire serial bus interface pointer register temperature hysteresis register state machine and digital comparator digital filter and control logic thermostat output configuration register bandgap sensor and reference result register temperature setpoint register the address speci?ed in the serial bit stream must be made to initiate communication. a1 and a0 should be connected directly to v dd or ground. when a2/t1 is used as an address bit input, it should also be tied to v dd or ground. a2/t1 can alternatively connect to a remote temperature sensor. when a2/t1 is used for temperature measurements, an off-chip di- ode junction must be connected between a2/t1 and gr ound. in this case, internal circuitry will detect a2 as logic low, leaving four possible slave addresses. see temperature measure- ment and power on for more information. a2/t1, a1, and a0 determine the slave address as shown in table 1. int temperature events are indicated to external circuitry via this output. int may be con?gured as active-low or active-high by the host. operation of the int output is controlled by the mode and pol bits in the mic184s con?guration register. see comparator and interrupt modes below. this output is open-drain and may be wire-ored with other open-drain signals. most systems will require a pull-up resistor or current source on this pin. if the im bit in the con?guration register is set, it prevents the int output from sinking current. in i 2 c and smbus systems, the im bit is therefore an interrupt mask bit. downloaded from: http:///
may 2006 7 mic184 mic184 micrel stupni sserddaevals481cim 1t/2a 1a 0a yranib xeh 0 0 0 0001001 b 84 h 0 0 1 1001001 b 94 h 0 1 0 0101001 b a4 h 0 1 1 1101001 b b4 h 1 0 0 0011001 b c4 h 1 0 1 1011001 b d4 h 1 1 0 0111001 b e4 h 1 1 1 1111001 b f4 h edoid 0 0 0001001 b 84 h edoid 0 1 1001001 b 94 h edoid 1 0 0101001 b a4 h edoid 1 1 1101001 b b4 h table 1. mic184 slave address settings temperature measurement the temperature-to-digital converter for both internal and external temperature data is built around a switched current source and a 9-bit analog-to-digital converter. the tem- perature is calculated by measuring the forward voltage of a diode junction at two different bias current levels. an internal multiplexer directs the current sources output to either an internal or external diode junction. the mic184 uses twos-complement data to represent temperatures. if the msb of a temperature value is 0, the temperature is 0c. if the msb is 1, the temperature is < 0. more detail on this is given in temperature data for- mat below. a temperature event results if the value in the temperature result register (temp) is greater than the value in the overtemperature setpoint register (t_set), or if it is less than the value in the temperature hysteresis register (t_hyst). the value of the zone bit in the con?guration register deter- mines whether readings are taken from the on-chip sensor or from the a2/t1 input. at power-up, the zone bit of the con?guration register is set to zero. the mic184 therefore monitors its internal temperature and compares the result against the contents of t_set and t_hyst. setting t he zone bit in config will result in the mic184 acquiring temperature data from an external diode connected to the a2/t1 pin. this diode may be embedded in an integrated circuit (such as a cpu, asic, or graphics processor), or it may be a diode-con- nected discrete transistor. once the new value is written to config, the a/d converter will begin a new conversion and return temperature data from the external zone. this data will be compared against t_set, t_hyst, and the state of the fault_queue (described below). the internal status bit (sts) and the int output will then be updated accordingly. see applications information for more details on switching between zones. diode faults the mic184 is designed to respond in a fail-safe manner to hardware faults in the external sensing circuitry. if the con- nection to the external diode is lost, or the sense line (a2/t1) is shorted to v dd or ground, the temperature data reported by the a/d converter will be forced to its full-scale value (+127.5c). this will cause an overtemperature event to oc- cur whenever t_set +127.0c (0 1111 1110 b ). an interrupt will be generated if so enabled. the temperature reported for the external zone will remain 0 1111 1111 b = +127.5c until the fault condition is cleared. this fault detection requires that the mic184 complete the number of conversion cycles speci?ed by fault_queue. the mic184 may therefore r equire one or more conversion cycles following power-on or a transi- tion from shutdown to normal operation before reporting an external diode fault. serial port operation the mic184 uses standard smbus write_byte, read_ byte, write_word, and read_word operations for communication with its host. the smbus write_byte and write_word operations involve sending the devices slave address (with the r/w bit low to signal a write operation), followed by a command byte and one or two data bytes. the smbus read_byte operation is similar, but is a composite write and read operation: the host ?rst sends the devices slave address followed by the command byte, as in a write operation. a new start bit must then be sent to the mic184, 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 etyb_dnammoc retsigertegrat yranib xeh lebal noitpircsed 00000000 b 00 h pmet tlusererutarepmetderusaem 10000000 b 10 h gifnoc retsigernoitarugifnoc 01000000 b 20 h tsyh_t siseretsyherutarepmet 11000000 b 30 h tes_t tniopteserutarepmetrevo 00100000 b 40 h devreser esutonod 11111111 b ff h table 2. mic184 register addresses downloaded from: http:///
mic184 micrel mic184 8 may 2006 s 1 0 0 1 a2 a1 a0 0 a 0 0 0 0 0 0 x x a d4 d5 d6 d3 d2 d1 d0 d7 /a p mic184 slave address data clk command byte data byte to?mic184 start stop r/w?=?write acknowledge acknowledge not acknowledge figure 1. write_byte protocol s 1 0 0 1 a2 a1 a0 a2 a1 a0 0 a 0 0 0 0 0 0 x x a s 1 1 1 0 0 d4 d5 d6 d3 d2 d1 d0 a d7 /a p mic184 slave address data clk command byte mic184 slave address data read from?mic184 start start stop r/w?=?write r/w?=?read acknowledge acknowledge acknowledge not acknowledge figure 2. read_byte protocol s 1 0 0 1 a2 a1 a0 0 a 0 0 0 0 0 0 x x a d8 d7 d6 d5 d4 d3 d0 d1 a d0 x x x x x x x /a p mic184 slave address data clk command byte high-order byte to?mic184 low-order byte to?mic184 start stop r/w?=?write acknowledge acknowledge acknowledge not acknowledge figure 3. write_word protocol s 1 0 0 1 a2 a1 a0 0 a 0 0 0 0 0 0 x x a mic184 slave address data clk command byte start r/w?=?write acknowledge acknowledge s 1 0 0 1 a2 a1 a0 1 a a d4 d5 d6 d3 d2 d1 d0 d7 d8 /a p x x x x x x x mic184 slave address high-order byte?from?mic184 low-order byte?from?mic184 start stop r/w?=?read acknowledge acknowledge not acknowledge figure 4. read_word protocol s 1 0 0 1 a2 a1 a0 1 a a d4 d5 d6 d3 d2 d1 d0 d7 d8 /a p x x x x x x x mic184 slave address data clk high-order byte?from?mic184 low-order byte?from?mic184 start stop r/w?=?read acknowledge acknowledge not acknowledge master-to-slave?transmission slave-to-master response figure 5. receive_data from a 16-bit register downloaded from: http:///
may 2006 9 mic184 mic184 micrel s 1 0 0 1 a2 a1 a0 a x 1 x x x x x x x a mic184 slave address first byte?of transaction start acknowledge acknowledge r/w?=?write /a p xx x x x x x x last byte?of transaction a/d converter? in standby conversion? in progress new conversion? in progress new conversion begins conversion?interrupted by?mic184 acknowledge result? ready t conv stop not acknowledge figure 6. a/d converter timing a s s 1 0 0 0 a2 a1 a0 a2 a1 a0 0 a 0 0 0 0 0 0 0 1 a 1 0 1 0 0 xx x x x x x x /a p mic184 slave address temp exceeds?t_set?or?falls below?t_hyst mic184 slave address data int* command byte?=?01 h ?= config config value** start start stop r/w?=?write acknowledge acknowledge acknowledge r/w?=?read not acknowledge master-to-slave?transmission slave-to-master response t n/int t /int * assumes?int polarity?is?active?low. ** status?bits?in config?are?cleared to zero following?this?operation. figure 7. responding to interrupts downloaded from: http:///
mic184 micrel mic184 10 may 2006 the mic184 may then be clocked out. there is one excep- tion to this rule: if the location latched in the pointer register from the last write operation is known to be correct (i.e., points to the desired register), then the receive_data procedure may be used. to perform a receive_data, the host sends an address byte to select the slave mic184, and then retrieves the appropriate number (one or two) of data bytes. figures 1 through 5 show the formats for these data read and data write procedures. the command byte is 8 bits (1 byte) wide. this byte carries the address of the mic184 register to be operated upon, and is stored in the mic184s pointer register. the pointer register is a write-only register, which is implemented for backward compatibility to the national semiconductor lm75 and similar devices. the command byte (pointer register) values corre- sponding to the various mic184 register addresses a re shown in table 2. command byte values other than 0000 00xx b = 00 h through 03 h are reserved, and should not be used. the config register is 8 bits (1 byte) wide. therefore, com- munications with the config register will at a mini mum require a read_byte, write_byte, or a receive_byte. the temp, t_hyst, and t_set registers are logically nine bits wide. note, though, that these registers are physi- cally two bytes (one smbus word) wide within the mic184. properly communicating with the mic184 involves a 16-bit read_word or receive_word from, or write_word to, these registers. this is a requirement of the i 2 c/smbus serial data protocols, which only allow data transfers to occur in multiples of eight bits. temperature data format the lsb of each 9-bit logical register represents 0.5c. the values are in a twos complement format, wherein the most signi?cant bit (d8) represents the sign: 0 for positive tem- peratures and 1 for negative temperatures. the seven least signi?cant bits of each 16-bit physical register are unde?ned. therefore, physical bits d6 through d0 of the data read from these registers must be masked off, and the resulting binary value right justi?ed before using the data received. it is also possible to read only the ?rst byte of any of these three registers, sacri?cing 0.5c of resolution in exchange for somewhat simpler data handling. however, all writes to the t_set and t_hyst registers must be in the 16-bit write_word format. table 3 shows examples of the data format used by the mic184 for temperatures. a/d converter timing whenever the mic184 is not in its low power shutdown mode, the internal a/d converter (adc) attempts to make c ontinuous conversions unless interrupted by a bus transaction accessing the mic184. when the mic184 is accessed, the conversion in progress will be halted, and the partial result discarded. when the access of the mic184 is complete the adc will begin a new conversion cycle, with results valid t conv after that. figure 6 shows this behavior. t conv is twice as long for external conversions as it is for internal conversions. this al- lows the use of a ?lter capacitor on the a2/t1 input without a loss of accuracy due to the resulting longer settling times. power-on when power is initially applied, the mic184s inter nal registers are set to default states which make the mic184 completely backward compatible with the lm75. also at this time, the levels on the address inputs a2, a1, and a0 are read to es- tablish the devices slave address. the mic184s power-up default state can be summarized as follows: ? normal-mode operation (mic184 not in shutdown) ? zone is set to internal (on-chip temperature sensing) ? int function is set to comparator mode ? int output is set to active-low operation ? fault_queue depth = 1 ? interrupts are enabled (im = 0) ? t_set = +80c; t_hyst = +75c in order to accommodate the use of a2/t1 as a dual-purpose input, there is a weak pulldown on a2/t1 that will attempt to sink 25a from the pin to ground for t por following power- up of the mic184. this allows the mic184 to pull a2/t1 to a low state when a diode junction is connected from that pin to ground, and latch a zero as the a2 address value. if a2 is not to be used as a diode connection, it should be connected to v dd or ground. note that a fault in the external tempera- ture sensor (if used) may not be reported until one or more conversion cycles have been completed following power-on. see diode faults. shutdown mode setting the shdn bit in the con?guration register halts the otherwise continuous conversions by the a/d converter. the erutarepmet yranibwar yranibdeksam xehdeksam c521+ xxxxxxx010111110 010111110 b af0 h c52+ xxxxxxx010011000 010011000 b 230 h c5.0+ xxxxxxx100000000 100000000 b 100 h c0 xxxxxxx000000000 000000000 b 000 h c5.0C xxxxxxx111111111 111111111 b ff1 h c52C xxxxxxx011100111 011100111 b ec1 h c04C xxxxxxx000011011 000011011 b 0b1 h c55C xxxxxxx010010011 010010011 b 291 h table 3. digital temperature format downloaded from: http:///
may 2006 11 mic184 mic184 micrel mic184s power consumption drops to 1a typical in shutdown mode. all registers may be read from, or written to, while in shutdown mode. serial bus activity will slightly increase the mic184s power consumption. entering shutdown mode will not affect the state of int when the device is in comparator mode (mode = 0). however, if the device is shut down while in interrupt mode, the int pin will be deasserted and the internal latch (sts) holding the interrupt status will be cleared. therefore, no interrupts will be generated while the mic184 is in shutdown mode, and the interrupt status will not be retained. it is important to note, however, that the cause of the last temperature event will be retained in the mic184. this is described further in comparator and interrupt modes below. the diode fault detection mechanism (see diode faults) requires one or more a/d conversion cycles to detect external sensor faults. hence, no diode faults will be detected while the device is in shutdown. comparator and interrupt modes depending on the setting of the mode bit in the con?gura- tion register, the int output will behave either as an interrupt request signal or a thermostatic control signal. thermostatic operation is known as comparator mode . the int output is asserted whenever the measured temperature, as reported in the temp register, exceeds the threshold programmed in the t_set register for the number of conversions sp eci?ed by fault_queue (described below). in comparator mode, int will remain asserted unless and until the measured temperature falls below the value in the t_hyst register for fault_queue conversions. no action on the part of the host is required for operation in comparator mode. note that entering shutdown mode will not affect the state of int when the device is in comparator mode. in interrupt mode , once a temperature event has caused sts to be set, and the int output to be asserted, they will not be automatically deasserted when the measured temperature falls below t_hyst. they can only be deasserted by reading any of the mic184's internal registers or by putting the device into shutdown mode. if the most recent temperature event was an overtemperature condition, sts will not be set again, and int cannot be reasserted, until the device has detected that temp < t_hyst. similarly, if the most recent t emperature event was an undertemperature condition, sts will in be set again, and int cannot be reasserted, until the device has detected that temp > t_set. this keeps the internal logic of the mic184 backward compatible with that of the lm75 and similar devices. there is a software override for this: while the mic184 is operating in interrupt mode, the part can be unconditionally set to monitor for an overtemperature condi- tion, regardless of what caused the last temperature event. this is done by clearing the mode bit, and then immediately resetting it to 1. following this sequence the next temperature event detected will be an overtemperature condition, regard- less of whether the last temperature event was the result of an overtemperature or undertemperature condition. in both modes, the mic184 will be responsive to overtem- perature events upon power up. fault_queue a fault_queue (programmable digital ?lter) is provided in the mic184 to prevent false tripping due to thermal or electrical noise. two bits, config[4:3], set the depth of fault_queue. fault_queue then determines the number of consecutive temperature events (temp > t_set or temp < t_hyst) which must occur in order for the condition to be considered valid. as an example, assume the mic184 is in comparator mode, and config[4:3] is programmed with 10 b . then the measured temperature would have to exceed t_set for four consecutive a/d conversions before int would be asserted or the status bit set. similarly, temp would have to be less than t_hyst for four consecutive conversions before int would be reset. like any ?lter, the fault_queue function also has the effect of delaying the detection of temperature events. in th is example, it would take 4 t conv to detect a temperature event. the depth of fault_queue vs. d[4:3] of the con?guration register is shown in table 4. handling interrupts the mic184 may be either polled by the host, or request the hosts attention via the int pin. in the case of polled opera- tion, the host periodically reads the contents of config to check the state of the status bit. the act of reading config clears the status bit, sts. if more than one event that sets the status bit occurs before the host polls the mic184, only the fact that at least one such event has occurred will be apparent to the host. if temp < t_hyst or temp > t_set for fault_queue con- versions, the status bit sts will be set in the config register. this action cannot be masked. however, a temperature event will only generate an interrupt signal on int if inter- rupts from the mic184 are enabled (im = 0 and mode = 1 in the con?guration register). reading any register following an interrupt will cause int to be deasserted, and will clear sts. the host should read the contents of the con?guration register after receiving an interrupt to con?rm that the mic184 was the source of the interrupt. this is shown in figure 7. as noted above, putting the device into shutdown mode will also deassert int and clear sts. therefore, this usually should not be done before completing the appropriate inter- rupt service routine(s). since temperature-to-digital conversions continue while int is asserted, it is possible that temperature could change be- tween the mic184s assertion of its int output and the hosts response to the interrupt. it is good practice when servicing interrupts for the host to read the current tempera ture to con?rm that the condition that caused the interrupt still exists. ]3:4[gifnoc htpedeueuq_tluaf 00 *noisrevnoc1 10 snoisrevnoc2 01 snoisrevnoc4 11 snoisrevnoc6 gnittestluafed* table 4. fault_queue depth settings downloaded from: http:///
mic184 micrel mic184 12 may 2006 interrupt polarity selection the int output can be programmed to behave as an active- low signal or an active-high signal. the default is active-low. int polarity is selected by programming the appropr iate value into the polarity bit (pol) in the config register. clearing pol selects active-low interrupts; setting pol selects ac- tive-high interrupts. int is an open-drain digital output and may be wire-ored with other open-drain logic signals. most applications will require a pull-up resistor on this pin. whether the config registers pol bit is set to provide a current-sinking (low) or high-z (high) state at the int pin when sts is high, writing a one to im will put the int pin into a high- z state. this meets the requirement of an active-low interrupt for the smbus, while making im available as an int-forcing bit for those applications which employ an active-high int output (for example, software fan-control routines). lm75 compatibility the mic184 can be used interchangeably with the lm75 in existing applications. the mic184 offers several advantages over the lm75: ? ability to monitor a second, remote temperature ? interrupt masking capability ? status bit for software polling routines ? lower quiescent current ? supports single-byte reads from 16-bit registers ? no inadvertent 8-bit read bus lock-up issues the three msbs of the con?guration register (which power up as zeroes) are used to access the mic184s additional functions. these are reserved bits according to the lm75 speci?cation and, for the lm75, must always be written as zeroes. the msb of the mic184s status register is a status ?ag that does not exist in the lm75. this bit will be set to one whenever an overtemperature event occurs. this bit would never be set by an lm75. software should not depend on this bit being zero when using the mic184 as an lm75 upgrade. if at power-up the measured temperature is higher than t_set, the status bit will be set following the ?rst conversion by the a/d. see applications information for a method by which host software can use this fact to differentiate between an mic184 and an lm75. downloaded from: http:///
may 2006 13 mic184 mic184 micrel register set and programmers model internal register set eman noitpircsed etybdnammoc noitarepo tluafedpu-rewop pmet erutarepmetderusaem 00 h ylnodaertib-9 000000000 b c0 )1( gifnoc retsigernoitarugifnoc 10 h etirw/daertib-8 00000000 b )2eton( tsyh_t siseretsyh 20 h etirw/daertib-9 011010010 b c57+ tes_t tniopteserutarepmet 30 h etirw/daertib-9 000001010 b c08+ detailed register descriptions )etirw/daertib-8(gifnoc ]7[d ]6[d ]5[d ]4[d ]3[d ]2[d ]1[d ]0[d ylnodaer etirw/daer etirw/daer etirw/daer etirw/daer eti rw/daer etirw/daer tpurretni sutats )sts( tpurretni ksam )3( )mi( pmet tceles )enoz( eueuqtluaf htped )q_f( tni ytiralop )lop( tni/pmc edom )edom( nwodtuhs )ndhs( stib noitcnuf noitarepo sts )ylnodaer(sutatstpurretni enon=0,deruccotpurretni=1 mi ksamtpurretni delbasid=1,delbane=0 enoz noitceleserutarepmetetomer/lanretni lanretni=0,etomer=1 q_f htpedeueuq_tluaf ,snoisrevnoc2=10,noisrevnoc1=00 snoisrevnoc6=11,snoisrevnoc4=01 lop noitcelesytiraloptuptuotni wolevitca=0,hgihevitca=1 edom tpurretni/rotarapmoc niptnirofnoitcelesedom ,edomtpurretni=1 edomrotarapmoc=0 ndhs nwodtuhs/lamron noitcelesedomgnitarepo ,nwodtuhs=1 lamron=0 power-up default value: 0000 0000 b = 00 h (4) ? not in shutdown mode ? comparator mode ? int = active low ? fault_queue depth = 1 ? local temperature zone ? interrupts enabled. config command byte address: 0000 0001 b = 01 h (1) temp will contain measured temperature data for the selected zone after the completion of one conversion. (2) after the ?rst fault_queue conversions are complete, the status bit will be set if temp < t_hyst or temp > t_set. (3) setting im forces the open-drain int output into its high-z state. see int polarity selection. (4) after the ?rst fault_queue conversions are completed, the status bit will be set if temp < t_hyst or temp > t_set. downloaded from: http:///
mic184 micrel mic184 14 may 2006 t_set power-up default value: 0 1010 0000b (+80c) t_set command byte address: 0000 0011b = 03 h * the value in t_set is 9 logical bits in width, but due to the conventions of i 2 c/smbus, it is represented by 16 serial bits. system software should ignore unde?ned bits d[6:0] during register reads. bits [6:0] should be set to zero during register writes. see serial port operation" and temperature data format for more details. temperature setpoint register )etirw/daertib-9(tes_t ]51[d ]41[d ]31[d ]21[d ]11[d ]01[d ]9[d ]8[d ]7[d ]6[d ]5[d ] 4[d ]3[d ]2[d ]1[d ]0[d bsm 7tib 6tib 5tib 4tib 3tib 2tib 1tib bsl x x x x x x x tniopteserutarepmetrevo stib noitcnuf noitarepo ]7:51[d tnioptesrotarapmocerutarepmetrevo *etirw/daer t_hyst power-up default value: 0 1001 0110 b (+75c) t_hyst command byte address: 0000 0010b = 02 h * the value in t_hyst is 9 logical bits in width, but due to the conventions of i 2 c/smbus, it is represented by 16 serial bits. system software should ignore unde?ned bits d[6:0] during register reads. bits [6:0] should be set to zero during register writes. see "serial port operation" and temperature data format for more details. hysteresis register )etirw/daertib-9(tsyh_t ]51[d ]41[d ]31[d ]21[d ]11[d ]01[d ]9[d ]8[d ]7[d ]6[d ]5[d ] 4[d ]3[d ]2[d ]1[d ]0[d bsm 7tib 6tib 5tib 4tib 3tib 2tib 1tib bsl x x x x x x x gnittessiseretsyherutarepmet stib noitcnuf noitarepo ]7:51[d gnittessiseretsyherutarepmet *etirw/daer temperature result register )ylnodaertib-9(pmet ]51[d ]41[d ]31[d ]21[d ]11[d ]01[d ]9[d ]8[d ]7[d ]6[d ]5[d ] 4[d ]3[d ]2[d ]1[d ]0[d bsm 7tib 6tib 5tib 4tib 3tib 2tib 1tib bsl x x x x x x x cdamorfataderutarepmet stib noitcnuf noitarepo ]7:51[d ataderutarepmetderusaem enozdetcelesrof *ylnodaer power-up default value: 0 0000 0000 b = 0c ? temp command byte address: 0000 0000 b = 00 h * the value in temp is 9 logical bits in width, but due to the conventions of i 2 c/smbus, it is represented by 16 serial bits. system software should ignore unde?ned bits d[6:0]. see serial port operation" and "temperature data format for more details. ? temp will contain measured temperature data for the selected zone after the completion of one conversion. downloaded from: http:///
may 2006 15 mic184 mic184 micrel applications informationswitching zones the recommended procedure for switching between the internal and external zones is as follows: 1. disable interrupts (if used) by setting the im bit in config. 2. read the config register to: a) verify no masked interrupt was pending (d[7] = 0) b) clear sts prior to switching zones c) hold the settings of config register for the current zone 3. write the appropriate values to t_set and t_hyst for the new zone. 4. write to config as follows: a) to toggle the zone bit (1 = remote, 0 = internal) b) if interrupts are being used, step 4 should also clear mode 5. if interrupts are being used, mode must then be set to 1 and im reset to 0 at the conclusion of the serial bus transaction for step 4, the a/d converter will begin a conversion cycle using the new zone setting. the next conversion cycle completed after the serial bus transaction for step 5 will result in the state of the int output being updated (if enabled) for the new zone. generally the mic184s a/d converter operates conti nuously, but it will be halted and reset each time the part recognizes its slave address on the serial bus. interrupted conversions will remain halted until the end of the hosts communication with the mic184. after the completion of step 5 and a delay of t conv x fault_queue , sts and int will contain the results for the new zone. the above routine is extremely unlikely to miss a temperature event, as even one a/d conversion is typically much slower than the i 2 c/smbus transactions that control the mic184. see figure 6: a/d converter timing. step 2(c) is recommended because the mic184 has only one config register, corresponding to the active zone. in order to preserve data integrity for both zones, 2(c) allows the host to create a virtual config register for the inactive zone by dedicating one byte of memory to that purpose. additional virtual registers may be created as needed by inserting additional reads as steps 2(d), 2(e), etc. these could for example correspond to the values in t_set and t_hyst immediately prior to switching zones. steps 4(b) and 5 ensure that the mic184 will enter the new zone searching for an overtemperature event. identifying an mic184 by software test the mic184 and the lm75 each have an eight-bit con- fig register. in lm75-type parts, no more than seven of the eight bits of this register are used, and at least one bit (the msb) will always return a zero. the mic184 uses all eight bits of the config register: the msb is the parts status bit (sts). a simple test by which the host can determine whether a system has an mic184 installed, or is using a legacy lm75-type device, is to create a situation which will set the msb in the mic184s config register and then determine if the msb is in fact set. two examples of how this can be done are outlined below. the ?rst is in- terrupt-driven, the second uses software polling. note that both procedures generate one or more spurious interrupts. the code for these tests should therefore temporarily dis- able any affected interrupt routines. {start interrupt-driven test and initialization routine} 1. disable the hosts overtemperature and under- temperature interrupt handling routine. redirect interrupts from the part under test to a handler for the interrupt that will be generated in steps (4) and (7) of this routine. 2. write 0000 0010b (02h) to the config register. (the assumption is made that the host is an i 2 c or smbus part, and therefore responds to an ac- tive-low interrupt request.) 3. write 1100 1000 1000 0000b = c880h to t_set and t_hyst. this corresponds to -55.5c. 4. when the part has ?nished its ?rst a/d conver- sion, int will be asserted. 5. read out the contents of the config register: a) if the part is an mic184, the msb will be set to one (config = 1000 0010b = 82h). b) if the part is a conventional lm75-type part, the msb will be zero (config = 0000 0010b = 02h). 6.write 0111 1111 1000 0000b = 7f80h to t_set and t_hyst. this corresponds to +127.5c. 7.when the part has ?nished its next a/d conver- sion, int will be asserted a second time. 8.read config again, to clear the interrupt re- quest from step (7). this will also clear sts, if the part under test is an mic184. 9.based on the results of the test in step (4), do the following within 50ms total: a) set the config register as required. b) load t_hyst with its operational value. c) load t_set with its operational value. d) set the hosts interrupt handling routine back to overtemperature and undertemperature mode. {end} {start polling-based test and initialization rou- tine} 1. temporarily disable the hosts interrupt input downloaded from: http:///
mic184 micrel mic184 16 may 2006 from the device under test. 2. write 0000 0010b (02h) to the config register. 3. write 1100 1000 1000 0000b = c880h to t_set and t_hyst. this corresponds to -55.5c. 4. wait t conv (160ms max.) for the part to ?nish at least one a/d conversion. 5. read the contents of the config register: a) if the part is an mic184, the msb will be set to one (config = 82h). b) if the part is a conventional lm75-type part, the msb will be zero (config = 02h). 6. write 0111 1111 1000 0000b = 7f80h to t_set and t_hyst. this corresponds to +127.5c. 7. wait an additional t conv for the part to ?nish a second conversion. 8. read config again, to clear the interrupt request from step (7). this will also clear sts, if the part under test is an mic184. 9. based on the results of the test in step (4), do the following four steps within 50ms total: a) set the config register as required. b) load t_hyst with its operational value. c) load t_set with its operational value. d) re-enable the hosts interrupt handling input from the part under test. {end} these routines force the device under test to generate an overtemperature fault (steps 3 and 4), followed by an under- temperature fault (steps 6 through 8). this sequence causes the device under test to exit the routine prepared to respond to an overtemperature condition. if being immediately pre- pared to detect an undertemperature condition upon exit is desired, swap steps 3 and 6 in each routine. remote diode selection most small-signal pnp transistors with characteristics similar to the jedec 2n3906 will perform well as remote tempera- ture sensors. table 3 lists several examples of such parts. micrel has tested those marked with a bullet for use with the mic184. minimizing errors self-heating one concern when using a part with the temperature accuracy and resolution of the mic184 is to avoid errors induced by self-heating (v dd i dd ). in order to understand what level of error this might represent, and how to reduce that error, the dissipation in the mic184 must be calculated, and its effects examined as a temperature error. in most applications, the int output will be low for at most a few milliseconds before the host sets it back to the high state, making its duty cycle low enough that its contribution to self- heating of the mic184 is negligible. similarly, the data pin will in all likelihood have a duty cycle of substantially below 25% in the low state. these considerations, combined with more typical device and application parameters, allow the following calculation of typical device self-heating in inter- rupt-mode: p d = (i dd(typ.) 3.3v + 25% i ol(data) 0.3v + 1% i ol(int) 0.3v) p d = (0.3ma 3.3v + 25% 1.5ma 0.3v + 1% 1.5ma 0.3v) t j = 1.11mw 206c/w t j relative to t a is 0.23c if the part is to be used in comparator mode, calculations similar to those shown above (accounting for the expected value and duty cycle of i ol(int) ) will give a good estimate of the devices self-heating error. in any application, the best test is to verify performance against calculation in the ?nal application environment. this is especially true when dealing with systems for which some of the thermal data, (for example, pc board thermal conduc- tivity and/or ambient temperature), may be poorly de?ned or unavailable except by empirical means. series resistance the operation of the mic184 depends upon sensing the v cb-e of a diode-connected pnp transistor ("diode") at two different current levels. for remote temperature mea- surements, this is done using an external diode connected between a2/t1 and ground. since this technique relies upon measuring the rela tively 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 mic184. 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 mic184's temperature measurement. it is not dif?cult to keep the series resistance well below an ohm (typically 0.1), so vendor part number package tested fairchild mmbt3906 sot-23 ? on semiconductor mmbt3906l sot-23 ? phillips semiconductor pmbt3906 sot-23 ? rohm semiconductor sst3906 sot-23 samsung kst3906-tf sot-23 zetex fmmt3906 sot-23 table 5. transistors suitable for remote temperature sensing use downloaded from: http:///
may 2006 17 mic184 mic184 micrel in most systems this will not be an issue.filter capacitor selection when using a remote diode for temperature sensing, it is sometimes desirable to use a ?lter capacitor between the a2/t1 and gnd pins of the mic184. the use of this capaci- tor is recommended in environments with a signi?cant high frequency noise (such as digital switching noise), or if long wires are used to connect to the remote diode. the maximum recommended total capacitance from the a2/t1 pin to gnd is 2700pf. this usually suggests the use of a 2200pf np0 or c0g ceramic capacitor with a 10% tolerance. if the remote diode is to be at a distance of more than 6" ~ 12" from the mic184, using a shielded cable (solid foil shield microphone cable is a good choice) for the connections to the diode can signi?cantly help reduce noise pickup. remember to subtract the cable's conductor-to-shield capacitance from the 2700pf maximum total capacitance. layout considerations local mode only applications: if the mic184 is not going to be used with an external diode, the best layout is one which keeps it thermally coupled to the subsystem(s) whose temperature it must monitor, whi le avoid- ing any strong sources of emi, rfi, or electrostati cally coupled noise. two of the most common examples of such sources are switching power supply transformers and crts. remote mode applications: 1. if the remote sensing capability of the mic184 will be used in an application, place the mic184 as close to the remote diode as pos- sible, while taking care to avoid severe noise sources (high frequency power transformers, crts, memory and data busses, and the like). 2. since any conductance from the various volt- ages on the pc board and the a2/t1 pin can induce serious errors, it is good practice to guard the remote diodes emitter trace with a pair of ground traces. these ground traces should be returned to the mic184s 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 diodes own ground return back to the ground pin of the mic184, thereby providing a kelvin connection for the base of the diode. see figure 8. 3. when using the mic184 to sense the tempera- ture of a processor or other device which has an integral on-board diode (e.g., intels pentium ? iii), connect the emitter and base of the remote sensor to the mic184 using the guard traces and kelvin return shown in figure 8. the col- lector of the remote diode is inaccessible to the user on these types of chips. to allow for this, the mic184 has superb rejection of noise appearing from collector to gnd, as long as the base to ground connection is relatively quiet. 4. due to the small currents involved in the mea- surement of the remote diodes v be , it is important to adequately clean the pc board after soldering. this is most likely to show up as an issue in some situations where water-soluble soldering ?uxes are used. 5. in general, wider traces for the ground and a2/t1 pins will help reduce susceptibility to radi- ated noise (wider traces are less inductive). use trace widths and spacing of 10 mils wherever possible. wherever possible, place a ground plane under the mic184, and under the connec- tions from the mic184 to the remote diode. this will help guard against stray noise pickup. 6. always place a good quality v dd bypass ca- pacitor directly adjacent to, or underneath, the mic184. this part should be a 0.1f ceramic capacitor. surface-mount parts provide the best bypassing because of their low inductance. 7. when the mic184 is being powered from par- ticularly noisy power supplies, or from supplies which may have sudden high-amplitude spikes appearing on them, it can be helpful to add ad- ditional power supply ?ltering. this should be implemented as a 100 resistor in series with the parts v dd pin, and a 4.7f, 6.3v electrolytic capacitor from v dd to gnd. see figure 9. downloaded from: http:///
mic184 micrel mic184 18 may 2006 remote?diode?(a2/t1) guard/return 12 3 data clk int gnd 87 6 5 4 vdd a0a1 a2/t1 guard/return figure 8. guard traces/kelvin ground returns data 12 3 8 4 56 7 from serial bus host 2n3906 2200pf mic184 clkint vdd 100 3.0v to 3.6v 10k pull-ups a2/t1 a1a0 gnd 4.7f 0.1f figure 9. v dd decoupling for very noisy supplies downloaded from: http:///
may 2006 19 mic184 mic184 micrel package information 8-lead soic (m) 8-lead msop (mm) ???????????????????????? ???????????????????????? ???????????? ?????????????? ????????????????? ?????????????? ????? ????? ???????????????????????? ???????????????????????? ??????????? ???????????????????????? ???????????????????????? ???????????????????????? ??????????? ????????? ???????????????????????? downloaded from: http:///
mic184 micrel mic184 20 may 2006 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 byl micrel reserves the right to change circuitry and speci?cations at any time without noti?cation to t he customer. micrel products are noth 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 signi?cant injury to the user. a purchaser's use or sale of micrel prn micrel for any damages resulting from such use or sale. ? 2005 micrel incorporated downloaded from: http:///

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