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1 of 17 022103 features temperature measurements require no external components measures temperatures from -55c to +125c in 0.5c increments. fahrenheit equivalent is -67f to 257f in 0.9f increments temperature is read as a 9-bit value (2-byte transfer) wide power supply range (2.7v to 5.5v) converts temperature to digital word in 1 second thermostatic settings are user definable and nonvolatile data is read from/written via a 2-wire serial interface (open drain i/o lines) applications include thermostatic controls, industrial systems, consumer products, thermometers, or any thermal sensitive system 8-pin dip or so package (150mil and 208mil) pin assignment pin description sda - 2-wire serial data input/output scl - 2-wire serial clock gnd - ground t out - thermostat output signal a0 - chip address input a1 - chip address input a2 - chip address input v dd - power supply voltage description the DS1621 digital thermometer and thermostat provi des 9-bit temperature readings, which indicate the temperature of the device. the thermal alarm output, t out , is active when the temperature of the device exceeds a user-defined temperature th. the output remains active until the temperature drops below user defined temperature tl, a llowing for any hysteresis necessary. user-defined temperature settings are stored in nonvol atile memory so parts ma y be programmed prior to insertion in a system. temperature settings and temperature readings are all communicated to/from the DS1621 over a simple 2-wire serial interface. DS1621 digital thermometer and thermostat www.maxim-ic.com 6 3 1 2 4 8 7 5 sd a t out gnd v dd a 0 a 1 a 2 DS1621s 8-pin so (150mil) DS1621v 8-pin so (208mil) see mech drawings section 6 3 1 2 4 8 7 5 sd a scl t out gnd v dd a 0 a 1 a 2 DS1621 8-pin dip (300mil) see mech drawings section scl
DS1621 2 of 17 table 1. detailed pin description pin symbol description 1 sda data input/output pin for 2- wire serial communication port. 2 scl clock input/output pin for 2- wire serial communication port. 3t out thermostat output. active when temperature exceeds th; will reset when temperature falls below tl. 4 gnd ground pin. 5 a2 address input pin. 6 a1 address input pin. 7 a0 address input pin. 8v dd supply voltage input power pin. (2.7v to 5.5v) operation measuring temperature a block diagram of the DS1621 is shown in figure 1. the DS1621 measures temperatures through the use of an onboard proprietary temperature measurem ent technique. a block diagram of the temperature measurement circuitry is shown in figure 2. the DS1621 measures temperature by counting the number of clock cycles that an oscillator with a low temperature coefficient goes through during a gate period determined by a high temperature coefficient oscillator. the counter is preset with a base count that corresponds to -55 c. if the counter reaches 0 before the gate period is over the temperature register, which is also preset to the -55 c value, is incremented indicating that the temperature is higher than -55 c. at the same time, the counter is preset with a value determined by the slope accumulator circuitry. this circuitry is needed to compensate for the parabolic behavior of the oscillators over temperature. the counter is then clocked again until it reaches 0. if the gate period is still not finished, then this process repeats. the slope accumulator is used to compensate for the nonlinear behavior of the oscillators over temperature, yielding a high reso lution temperature measurement. this is done by changing the number of counts necessary for the counter to go through fo r each incremental degree in temperature. to obtain the desired resolution, both the value of the counter and the number of counts per c (the value of the slope accumulator) at a given temperature must be known. this calculation is done inside the DS1621 to provide 0.5 c resolution. the temperature reading is provided in a 9-bit, two?s complement readin g by issuing the read temperature command. table 2 describes the exact relationship of output data to measured temperature. the data is transmitted through the 2-wire serial interface, ms b first. the DS1621 can measure temperature over the range of -55 c to +125 c in 0.5 c increments. for fahrenheit usage a lookup ta ble or conversion factor must be used.
DS1621 3 of 17 figure 1. DS1621 functional block diagram status register & control logic temperature sensor high temp trigger , th low temp trigger , tl digital comparator/logic address and i/o control scl sd a a0 a1 a2 t out
DS1621 4 of 17 figure 2. temperature measuring circuitry table 2. temperature/data relationships temperature digital output (binary) digital output (hex) +125c 01111101 00000000 7b00h +25c 00011001 00000000 1900h +?c 00000001 00000000 0080h +0c 00000000 00000000 0000h -?c 11111111 10000000 ff80h -25c 11100111 00000000 e700h -55c 11001001 00000000 c900h since data is transmitted over the 2-wire bus msb first, temperature data may be written to/read from the DS1621 as either a single byte (w ith temperature resolution of 1 c) or as two bytes. the second byte would contain the value of the least significant (0.5 c) bit of the temperature reading as shown in table 1. note that the remaining 7 bits of this byte are set to all "0"s. temperature is represented in the DS1621 in terms of a ? c lsb, yielding the following 9-bit format: t = -25 c slope accumulator preset compare low temperature coefficient oscillator counter preset =0 temperature register high temperature coefficient oscillator counter =0 inc stop set/clear lsb 1 1 1 0 0 1 1 1 0 0 0 0 0 0 0 0 msb lsb
DS1621 5 of 17 higher resolutions may be obtained by reading the temperature and truncating the 0.5 c bit (the lsb) from the read value. this value is temp_read. the value left in the counter may then be read by issuing a read counter command. this value is the count remaining (count_remain) after the gate period has ceased. by loading the value of the sl ope accumulator into the count register (using the read slope command), this value may then be r ead, yielding the number of counts per degree c (count_per_c) at that temperature. the actual temp erature may be then be calculated by the user using the following: temperature=temp_read-0.25 + c per count remain count c per count _ _ ) _ _ _ ( thermostat control in its operating mode, the DS1621 functions as a ther mostat with programmable hysteresis as shown in figure 3. the thermostat output updates as s oon as a temperature conversion is complete. when the DS1621?s temperature meets or exceeds the va lue stored in the high temperature trip register (th), the output becomes active and will stay active until the temperature falls below the temperature stored in the low temperature trigger register (t l). in this way, any amount of hysteresis may be obtained. the active state for the output is programmable by the user so that an active state may either be a logic "1" (v dd ) or a logic "0" (0v). figure 3. thermostat output operation dq (thermostat output, active = high) operation and control the DS1621 must have temperature settings resident in the th and tl registers for thermostatic operation. a configuration/status register also dete rmines the method of operation that the DS1621 will use in a particular application, as well as indicating the status of the temperature conversion operation. the configuration register is defined as follows: where done = conversion done bit. ?1? = conversion complete, ?0? = conversion in progress. tl th t ( c ) done thf tlf n vb 1 0 pol 1shot
DS1621 6 of 17 thf = temperature high flag. this bit will be set to ?1? when the temperature is greater than or equal to the value of th. it will remain ?1? until reset by writing ?0? into this location or removing power from the device. this feature provides a method of de termining if the DS1621 has ever been subjected to temperatures above th while power has been applied. tlf = temperature low flag. this bit will be set to ?1? when the temperature is less than or equal to the value of tl. it will remain ?1? until reset by writing ?0? into this location or removing power from the device. this feature provides a method of dete rmining if the DS1621 has ever been subjected to temperatures below tl while power has been applied. nvb = nonvolatile memory busy flag. ?1? = write to an e 2 memory cell in progress, ?0? = nonvolatile memory is not busy. a copy to e 2 may take up to 10 ms. pol = output polarity bit. ?1? = active high, ?0? = active low. this bit is nonvolatile. 1shot = one shot mode. if 1shot is ?1?, the DS1621 will perform one temperature conversion upon receipt of the start convert t protocol. if 1shot is ?0?, the DS1621 will continuously perform temperature conversions. this bit is nonvolatile. for typical thermostat operation the DS1621 will operate in continuous mode. however, for applications where only one reading is needed at certain times or to conserve power, the one-shot mode may be used. note that the thermostat output (t out ) will remain in the state it was in after the last valid temperature conversion cycle when operating in one-shot mode. 2-wire serial data bus the DS1621 supports a bidirectional 2-wire bus and da ta transmission protocol. a device that sends data onto the bus is defined as a transmitter, and a device receiving data as a receiver. the device that controls the message is called a ?master." the devices that are controlled by the master are ?slaves." the bus must be controlled by a master device which generates the serial clock (scl), controls the bus access, and generates the start and stop conditions. the DS1621 operates as a slave on the 2-wire bus. connections to the bus are made via the open-drain i/o lines sda and scl. the following bus protocol has been defined (see figure 4): data transfer may be initiated only when the bus is not busy. during data transfer, the data line must remain stable whenever the clock line is high. changes in the data line while the clock line is high will be interpreted as control signals. accordingly, the following bus conditions have been defined: bus not busy: both data and clock lines remain high. start data transfer: a change in the state of the data line, from high to low, while the clock is high, defines a start condition. stop data transfer: a change in the state of the data line, from low to high, while the clock line is high, defines the stop condition.
DS1621 7 of 17 data valid: the state of the data line represents valid da ta when, after a start condition, the data line is stable for the duration of the high period of th e clock signal. the data on the line must be changed during the low period of the clock signal. th ere is one clock pulse per bit of data. each data transfer is initiated with a start c ondition and terminated with a stop condition. the number of data bytes transferred between start and stop conditions is not limited and is determined by the master device. the information is transfer red byte-wise and each receiver acknowledges with a ninth-bit. within the bus specifications a regular mode (100khz clock rate) and a fast m ode (400khz clock rate) are defined. the DS1621 works in both modes. acknowledge: each receiving device, when addressed, is obl iged to generate an acknowledge after the reception of each byte. the master device must generate an extra clock pulse which is associated with this acknowledge bit. a device that acknowledges must pull down the sda lin e during the acknowledge clock pulse in such a way that the sda line is stable low during the high period of the acknowledge related clock pulse. of course, setup and hold times must be taken into account . a master must signal an end of data to the slave by not generating an acknowledge bit on the last byte th at has been clocked out of the slave. in this case, the slave must leave the data line high to enable the master to generate the stop condition. figure 4. data transfer on 2-wire serial bus figure 4 details how data transfer is accomplishe d on the 2-wire bus. depending upon the state of the r/w bit, two types of data transfer are possible: 1. data transfer from a master transmitter to a slave receiver. the first byte transmitted by the master is the slave address. next follows a numbe r of data bytes. the slave returns an acknowledge bit after each received byte. 2. data transfer from a slave transmitter to a master receiver. the first byte, the slave address, is transmitted by the master. the slave then returns an acknowledge bit. next follows a number of data bytes transmitted by the slave to the master . the master returns an acknowledge bit after all received bytes other than the last byte. at the end of the last received byte, a ?not acknowledge? is returned.
DS1621 8 of 17 the master device generates all of the serial clock pulses and the start and stop conditions. a transfer is ended with a stop condition or with a repeated start condition. since a repeated start condition is also the beginning of the next serial transfer, the bus will not be released. the DS1621 may operate in the following two modes: 1. slave receiver mode: serial data and clock are received through sda and scl. after each byte is received an acknowledge bit is transmitted. start and stop conditions are recognized as the beginning and end of a serial tran sfer. address recognition is perform ed by hardware after reception of the slave address and direction bit. 2. slave transmitter mode: the first byte is received and handled as in the slave receiver mode. however, in this mode the direction bit will indicate that the transfer direction is reversed. serial data is transmitted on sda by the DS1621 while the se rial clock is input on scl. start and stop conditions are recognized as the begi nning and end of a serial transfer. slave address a control byte is the first byte received followi ng the start condition from the master device. the control byte consists of a 4-bit control code; for the DS1621, this is set as 1001 binary for read and write operations. the next 3 bits of the control byte are th e device select bits (a2, a1, a0). they are used by the master device to select which of eight devices are to be accessed. these bits are in effect the 3 least significant bits of the slave address. the last bit of the control byte (r/ w ) defines the operation to be performed. when set to a ?1? a read operation is selected, when set to a ?0? a write operation is selected. following the start condition the DS1621 monitors th e sda bus checking the device type identifier being transmitted. upon receiving th e 1001 code and appropriate device select bits, the slave device outputs an acknowledge signal on the sda line.
DS1621 9 of 17 figure 5. 2-wire serial communication with DS1621
DS1621 10 of 17 command set data and control information is r ead from and written to the DS1621 in the format shown in figure 5. to write to the DS1621, the master will issue the slave address of the DS1621 and the r/ w bit will be set to ?0?. after receiving an acknowledge, the bus mast er provides a command protocol. after receiving this protocol, the DS1621 will issue an acknowledge and then the master may send data to the DS1621. if the DS1621 is to be read, the master must send the comma nd protocol as before and then issue a repeated start condition and the control byte again, this time with the r/ w bit set to ?1? to allow reading of the data from the DS1621. the command set for the ds 1621 as shown in table 3 is as follows: read temperature [aah] this command reads the last temperature conversion result. the DS1621 will send 2 bytes, in the format described earlier, which are the contents of this register. access th [a1h] if r/ w is ?0? this command writes to the th (high temperature) register. after issuing this command, the next 2 bytes written to the DS1621, in the same format as described for reading temperature, will set the high temperature threshold for operation of the t out output. if r/ w is ?1? the value stored in this register is read back. access tl [a2h] if r/ w is ?0? this command writes to the tl (low temperature) register. after issuing this command, the next 2 bytes written to the DS1621, in the same format as described for reading temperature, will set the high temperature threshold for operation of the t out output. if r/ w is ?1? the value stored in this register is read back. access config [ach] if r/ w is ?0? this command writes to the configurati on register. after issuing this command, the next data byte is the value to be written into the configuration register. if r/ w is ?1? the next data byte read is the value stored in the configuration register. read counter [a8h] this command reads the value of the counter byte. this command is valid only if r/ w is ?1?. read slope [a9h] this command reads the value of the slope counter byte from the DS1621. this command is valid only if r/ w is ?1?. start convert t [eeh] this command begins a temperature conversion. no further data is required. in one-shot mode the temperature conversion will be performed and then the DS1621 will remain idle. in continuous mode this command will initiate c ontinuous conversions. stop convert t [22h] this command stops temperature conversion. no furthe r data is required. this command may be used to halt a DS1621 in continuous convers ion mode. after issuing this command, the current temperature
DS1621 11 of 17 measurement will be completed a nd the DS1621 will remain idle until a start convert t is issued to resume continuous operation. table 3. DS1621 command set instruction description protocol 2-wire bus data after issuing protocol notes temperature conversion commands read temperature read last converted temperature value from temperature register. aah read counter reads value of count remaining from counter. a8h read slope reads value of the slope accumulator. a9h start convert t in itiates temperature conversion. eeh idle 1 stop convert t halts temperature conversion. 22h idle 1 thermostat commands access th reads or writes high temperature limit value into th register. a1h 2 access tl reads or writes low temperature limit value into tl register. a2h 2 access config reads or writes configuration data to configuration register. ach 2 notes: 1. in continuous conversion mode a stop convert t command will halt c ontinuous conversion. to restart the start convert t command must be issu ed. in one-shot mode a start convert t command must be issued for every temperature reading desired. 2. writing to the e 2 typically requires 10ms at room temper ature. after issuing a write command, no further writes should be requested for at least 10ms.
DS1621 12 of 17 memory function example example: bus master sets up DS1621 for con tinuous conversion and th ermostatic function. bus master mode DS1621 mode data (msb first) comments tx rx start bus master in itiates a start condition. tx rx bus master sends DS1621 address; r/ w = 0. rx tx ack DS1621 generates acknowledge bit. tx rx ach bus master sends ac cess config command protocol. rx tx ack DS1621 generates acknowledge bit. tx rx 02h bus master sets up DS1621 for output polarity active high, continuous conversion. rx tx ack DS1621 generates acknowledge bit. tx rx start bus master generate s a repeated start condition. tx rx bus master sends DS1621 address; r/ w = 0. rx tx ack DS1621 generates acknowledge bit. tx rx a1h bus master sends access th command. rx tx ack DS1621 generates acknowledge bit. tx rx 28h bus master sends first byte of data for th limit of +40c. rx tx ack DS1621 generates acknowledge bit. tx rx 00h bus master sends second byte of data for th limit of +40c. rx tx ack DS1621 generates acknowledge bit. tx rx start bus master generate s a repeated start condition. tx rx bus master sends DS1621 address; r/ w = 0. rx tx ack DS1621 generates acknowledge bit. tx rx a2h bus master sends access tl command. rx tx ack DS1621 generates acknowledge bit. tx rx 0ah bus master sends first byte of data for tl limit of +10c. rx tx ack DS1621 generates acknowledge bit. tx rx 00h bus master sends second byte of data for tl limit of +10c. rx tx ack DS1621 generates acknowledge bit. tx rx start bus master generate s a repeated start condition. tx rx bus master sends DS1621 address; r/ w = 0. rx tx ack DS1621 generates acknowledge bit. tx rx eeh bus master sends start convert t command protocol. rx tx ack DS1621 generates acknowledge bit. tx rx stop bus master in itiates stop condition.
DS1621 13 of 17 absolute maximum ratings* voltage on any pin relativ e to ground -0.5v to +6.0v operating temperature range -55 c to +125 c storage temperature range -55 c to +125 c soldering temperature see ipc/jedec j-std-020a specification * this is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. exposure to absolute maximum rating conditions for extended periods of time may affect reliability. recommended dc operating conditions parameter symbol min typ max units notes supply voltage v dd 2.7 5.5 v 1 dc electrical characteristics (-55c to +125c; v dd = 2.7v to 5.5v) parameter symbol condition min typ max units notes thermometer error t err 0c to 70c 3.0v v dd 5.5v ? c 0c to 70c 2.7v v dd 3.0v 1c 11 -55c to +0c and 70c to 125c see typical curve thermometer resolution 12 bits low level input voltage v il 0.5 0.3 v dd v high level input voltage v ih 0.7 v dd v dd +0.3 v pulse width of spikes which must be suppressed by the input filter t sp fast mode 0 50 ns v ol1 3 ma sink current 0 0.4 v low level output voltage v ol2 6 ma sink current 0 0.6 v input current each i/o pin 0.4 DS1621 14 of 17 active supply current i cc temperature conversion -55c to +85c temperature conversion +85c to +125c e 2 write communication only 1000 1250 400 110 a 3, 4 standby supply current i stby 1 a 3, 4 v oh 1 ma source 2.4 v thermostat output (t out ) output voltage v ol 4 ma sink 0.4 v
DS1621 15 of 17 ac electrical characteristics (-55c to +125c; v dd = 2.7v to 5.5v) parameter symbol condition min typ max units notes temperature conversion time t tc 0.4 1 s nv write cycle time t wr 0c to 70c 10 50 ms 10 scl clock frequency f scl fast mode standard mode 0 0 400 100 khz bus free time between a stop and start condition t buf fast mode standard mode 1.3 4.7 s hold time (repeated) start condition t hd:sta fast mode standard mode 0.6 4.0 s 5 low period of scl clock t low fast mode standard mode 1.3 4.7 s high period of scl clock t high fast mode standard mode 0.6 4.0 s setup time for a repeated start condition t su:sta fast mode standard mode 0.6 4.7 s data hold time t hd:dat fast mode standard mode 0 0 0.9 s 6, 7 data setup time t su:dat fast mode standard mode 100 250 ns 8 rise time of both sda and scl signals t r fast mode standard mode 20+0.1c b 300 1000 ns 9 fall time of both sda and scl signals t f fast mode standard mode 20+0.1c b 300 300 ns 9 setup time for stop condition t su:sto fast mode standard mode 0.6 4.0 s capacitative load for each bus line c b 400 pf all values referred to v ih =0.9 v dd and v il =0.1 v dd . ac electrical characteristics (-55c to +125c; v dd = 2.7v to 5.5v) parameter symbol min typ max units notes input capacitance c i 5pf
DS1621 16 of 17 notes: 1. all voltages are referenced to ground. 2. i/o pins of fast mode devices must not obstruct the sda and scl lines if v dd is switched off. 3. i cc specified with t out pin open. 4. i cc specified with v cc at 5.0v and sda, scl = 5.0v, 0c to 70c. 5. after this period, the first clock pulse is generated. 6. a device must internally provide a hold time of at least 300ns for the sda signal (referred to the v ih min of the scl signal) in order to bridge th e undefined region of the falling edge of scl. 7. the maximum t hd:dat has only to be met if the device does not stretch the low period (t low ) of the scl signal. 8. a fast mode device can be used in a st andard mode system, but the requirement t su:dat >250ns must then be met. this will automatically be the case if the device does not stretch the low period of the scl signal. if such a device does stretch the lo w period of the scl signal, it must output the next data bit to the sda line t rmax + t su:dat = 1000 + 250 = 1250ns before the scl line is released. 9. c b ?total capacitance of one bus line in pf. 10. writing to the nonvolatile memory should only take place in the 0 c to 70 c temperature range. 11. see typical curve for specification limits outside 0c to 70c range. thermometer error reflects sensor accuracy as tested during calibration. timing diagram
DS1621 17 of 17 typical performance curve DS1621 digital thermometer and thermostat temperature reading error temperature ( c)

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