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| 1 of 13 080602 features requires no external components supply voltage range covers from 2.7v to 5.5v measures temperatures from ?5 c to +12 c in 0. c increments. fahrenheit equivalent is ?6 f to +25 f in 0. f increments temperature is read as a 9?bit value converts temperature to digital word in 1 second (max) thermostatic settings are user?definable and non?volatile data is read from/written via a 3?wire serial interface (clk, dq, rst ) applications include thermostatic controls, industrial systems, consumer products, thermometers, or any thermally sensitive system 8?pin soic (208 mil) package pin assignment pin description dq ? 3?wire input/output clk/ conv ? 3?wire clock input and stand?alone convert input rst ? 3?wire reset input gnd ? ground t high ? high temperature trigger t low ? low temperature trigger t com ? high/low combination trigger v dd ? power supply voltage (3v-5v) description the DS1720 digital thermometer and thermostat pr ovides 9?bit temperature readings which indicate the temperature of the device. with three thermal al arm out-puts, the DS1720 can also act as a thermostat. t high is driven high if the DS1720?s temperature is gr eater than or equal to a user?defined temperature th. t low is driven high if the DS1720?s temperature is less than or equal to a user?defined temperature tl. t com is driven high when the temperature exceed s th and stays high until the temperature falls below that of tl. user?defined temperature settings are stored in non?vol atile memory, so parts can be programmed prior to insertion in a system, as well as used in stand?a lone applications without a cpu. temperature settings and temperature readings are all communicated to/from the DS1720 over a simple 3?wire interface. DS1720 econ-digital thermometer and thermostat www.maxim-ic.com DS1720s 8-pin soic (208-mil) see mech. drawings section 1 2 3 4 8 7 6 5 dq clk/conv rst gnd v dd t high t low t com
DS1720 2 of 13 operation?measuring temperature a block diagram of the DS1720 is shown in figure 1. the DS1720 measures temperatures through the use of an on?board proprietary temperature measurem ent technique. a block diagram of the temperature measurement circuitry is shown in figure 2. the DS1720 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 w ith a base count that corresponds to ?5 c. if the counter reaches zero before the gate period is over, the temperature register, which is also preset to the ?5 c value, is incremented, indicating that the temperature is higher than ?5 c. at the same time, the counter is then 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 c ounter is then clocked again until it reaches zero. 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. th is 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, therefore, both the value of th e counter and the number of counts per degree c (the value of the slope accumulator) at a given temperature must be known. DS1720 functional block diagram figure 1 DS1720 3 of 13 temperature measuring circuitry figure 2 this calculation is done inside the DS1720 to provide 0. c resolution. the temperature reading is provided in a 9?bit, two?s complement reading by issuing a read temperature command. table 1 describes the exact relationship of output data to measured temperature. the data is transmitted serially through the 3?wire serial interface, lsb first. the DS1720 can measure temperature over the range of ?5 c to +12 c in 0. c increments. for fahrenheit usage, a l ookup table or conversion factor must be used. temperature/data rela tionships table 1 temp digital output (binary) digital output (hex) +85 c 0 10101010 00aa +25 c 0 00110010 0032h +? c 0 00000001 0001h +0 c 0 00000000 0000h -? c 1 11111111 01ffh -25 c 1 11001110 01ceh since data is transmitted over the 3?wire bus lsb first, temperature data can be written to/read from the DS1720 as either a 9?bit word (taking rst low after the 9 th (msb) bit), or as two transfers of 8?bit words, with the most significant 7 bits being ignored or set to zero, as illustrated in table 1. after the msb, the DS1720 will output 0s. note that temperature is represen ted in the DS1720 in terms of a ? c lsb, yielding the following 9?bit format: msb lsb xxxxxxx 1 1 1 0 0 1110 t = -25 c DS1720 4 of 13 higher resolutions may be obtained by reading the temperature, and truncating the 0. 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 + detailed pin description table 2 pin symbol description 1dq data input/output pin for 3?wire communication port. 2 clk/ conv clock input pin for 3?wire communication port. when the DS1720 is used in a stand?alone application with no 3?wire port, this pin can be used as a convert pin. temperature conversion will begin on the falling edge of conv . 3 rst reset input pin for 3?wire communication port. 4 gnd ground pin. 5t com high/low combination trigge r. goes high when temperature exceeds th; will reset to low when temperature falls below tl. 6t low low temperature trigge r. goes high when temperature falls below tl. 7t high high temperature trigge r. goes high when temperature exceeds th. 8v dd supply voltag e. 2.7v ? 5.5v input power pin. operation?thermostat controls three thermally triggered outputs, t high , t low , and t com , are provided to allow the DS1720 to be used as a thermostat, as shown in figure 3. when the DS1720?s temperature meets or exceeds the value stored in the high temperature trip register, the output t high becomes active (high) and remains active until the DS1720?s measured temperature becomes less than the st ored value in the high temperature register, th. the t high output can be used to indicate that a high temperature tolerance boundary has been met or exceeded, or as part of a closed l oop system can be used to activate a cooling system and to deactivate it when the system temperature returns to tolerance. the t low output functions similarly to the t high output. when the DS1720?s measured temperature equals or falls below the value stored in the low temperature register, the t low output becomes active. t low remains active until the DS1720?s temperature become s greater than the value stored in the low temperature register, tl. the t low output can be used to indicate that a low temperature tolerance boundary has been met or exceeded, or as part of a cl osed loop system, can be used to activate a heating system and to deactivate it when the system temperature returns to tolerance. the t com output goes high when the measured temperatur e meets or exceeds th, and will stay high until the temperature equals or falls below tl. in this way, any amount of hysteresis can be obtained. (count_per_c? count_remain) count_per_c DS1720 5 of 13 thermostat output operation figure 3 operation and control the DS1720 must have temperature settings resident in the th and tl registers for thermostatic operation. a configuration/status regi ster is also used to determine the method of operation that the DS1720 will use in a particular applic ation, as well as indicating the stat us of the temperature conversion operation. the configuration regi ster is defined as follows: configuration/status register done thf tlf nvb 1 0 cpu 1shot where done = conversion done bit. 1=conversi on complete, 0=conv ersion in progress. 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 by removing power from the device. this feature provides a method of deter mining if the DS1720 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 by removing power from the device. this feature provides a method of deter mining if the DS1720 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. cpu = cpu use bit. if cpu=0, the clk/ conv pin acts as a conversion start control, when rst is low. if cpu is 1, the DS1720 will be used with a cpu communicating to it over the 3?wire port, and the operation of the clk/ conv pin is as a normal clock in concert with dq and rst . this bit is stored in nonvolatile e 2 memory, capable of at least 50,000 write s. the DS1720 is shipped with cpu=0. 1shot = one?shot mode. if 1shot is 1, the ds 1720 will perform one temperature conversion upon reception of the start convert t protocol. if 1shot is 0, the DS1720 will continuously perform temperature conversion. this bit is stored in nonvolatile e 2 memory, capable of at least 50,000 writes. the DS1720 is shipped with 1shot=0. DS1720 6 of 13 for typical thermostat operation, the DS1720 will operate in continuous mode. however, for applications where only one reading is needed at certain times, and to conserve power, the one?shot mode may be used. note that the thermostat outputs (t high , t low , t com ) will remain in the state they were in after the last valid temperature conversion cycl e when operating in one?shot mode. operation in stand?alone mode in applications where the DS1720 is used as a simple thermost at, no cpu is required. since the temperature limits are nonvolatile, the DS1720 can be pr ogrammed prior to insertion in the system. in order to facilitate operation without a cpu, the clk/ conv pin (pin 2) can be used to initiate conversions. note that the cpu bit must be set to 0 in the configuration register to use this mode of operation. whether cpu=0 or 1, the 3?wire port is activ e. setting cpu=1 disables the stand?alone mode. to use the clk/ conv pin to initiate conversions, rst must be low and clk/ conv must be high. if clk/ conv is driven low and then brought high in le ss than 10 ms, one temperature conversion will be performed and then the DS1720 will return to an idle state. if clk/ conv is driven low and remains low, continuous con-versions will take place until clk/ conv is brought high again. with the cpu bit set to 0, the clk/ conv will override the 1?shot bit if it is equal to 1. this means that even if the part is set for one?shot mode, driving clk/ conv low will initiate conversions. 3?wire communications the 3?wire bus is comprised of three signals. these are the rst (reset) signal, the clk (clock) signal, and the dq (data) signal. all data transfers are initiated by driving the rst input high. driving the rst input low terminates communication. (see figures 4 and 5). a clock cycle is a sequence of a falling edge followed by a rising edge. for data inputs, the data mu st be valid during the rising edge of a clock cycle. data bits are output on the falling edge of the clock, and remain valid through the rising edge. when reading data from the DS1720, the dq pin goes to a high impedance state while the clock is high. taking rst low will terminate any communication and cause the dq pin to go to a high impedance state. data over the 3?wire interface is communicated lsb first. the command set for the 3?wire interface as shown in table 3 is as follows; only these protoc ols should be written to the DS1720, as writing other protocols to the device may result in permanent damage to the part. read temperature [aah] this command reads the contents of the register wh ich contains the last temperature conversion result. the next nine clock cycles will output the contents of this register. write th [01h] this command writes to the th (high temperature ) register. after issuing this command, the next nine clock cycles clock in the 9?bit temperature limit which will set the threshold for operation of the t high output. write tl [02h] this command writes to the tl (low temperature ) register. after issuing this command, the next nine clock cycles clock in the 9?bit temperature limit which will set the threshold for operation of the t low output. DS1720 7 of 13 read th [a1h] this command reads the value of the th (high temperature) register. after issuing this command, the next nine clock cycles clock out the 9?bit temperature limit which sets the threshold for operation of the t high output. read tl [a2h] this command reads the value of the tl (low tem perature) register. after issuing this command, the next nine clock cycles clock out the 9?bit temperature limit which sets the threshold for operation of the t low output. read counter [a0h] this command reads the value of the counter byte. the next nine clock cycles will output the contents of this register. read slope [a9h] this command reads the value of the slope counter byte from the DS1720. the next nine clock cycles will output the contents of this register. 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 DS1720 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 DS1720 in continuous convers ion mode. after issuing this command, the current temperature measurement will be completed, and then the DS1720 will remain idle un til a start convert t is issued to resume continuous operation. write config [0ch] this command writes to the configur ation register. after issuing this command, the next eight clock cycles clock in the value of the configuration register. read config [ach ] this command reads the value in the configuration register. after issuing this command, the next eight clock cycles output the value of the configuration register. DS1720 8 of 13 DS1720 command set table 3 instruction description protocol 3-wire bus data after issuing protocol notes temperature conversion commands read temperature temperatu re reads last converted temperature value from temperature register aah DS1720 9 of 13 function example example: cpu sets up DS1720 for continuous conversion and ther mostatic function. cpu mode DS1720 mode (3-wire) data (lsb first) comments tx rx 0ch tcpu issues write config command tx rx 00h cpu sets DS1720 up for continuous conversion tx rx toggle rst cpu issues reset to DS1720 tx rx 01h cpu issues write th command tx rx 0050h cpu sends data for th limit of +4 c tx rx toggle rst cpu issues reset to DS1720 tx rx 02h cpu issues write tl command tx rx 0014h cpu sends data for tl limit of +1 c tx rx toggle rst cpu issues reset to DS1720 tx rx a1h cpu issues read th command rx tx 0050h DS1720 sends back stored value of th for cpu to verify tx rx toggle rst cpu issues reset to DS1720 tx rx a2h cpu issues read tl command rx tx 0014h DS1720 sends back stored value of tl for cpu to verify tx rx toggle rst rst cpu issues reset to DS1720 tx rx eeh cpu issues start convert t command tx rx toggle rst cpu issues reset to DS1720 DS1720 10 of 13 read data transfer figure 4 write data transfer figure 5 related application notes the following application notes can be applied to the DS1720. these notes can be obtained from the dallas semiconductor ?applicati on note book?, via our web-site at http:\\www.dalsemi.com/, or through our faxback service at (972) 371?4441. application note 67: ?applying and using th e ds1620 in temperature control applications? application note 85: ?interfacing the ds1620 to the motorola spi bus? application note 105: ?high resolution temperat ure measurement with dallas direct?to?digital temperature sensors? sample DS1720 subroutines that can be used in conjunction with an105 can be downloaded from the web-site or our a nonymous ftp site. DS1720 11 of 13 absolute maximum ratings* voltage on any pin relativ e to ground ?0.5v to +7.0v operating temperature ?5 c to +12 c storage temperature ?5 c to +12 c soldering temperature 26 c for 10 seconds *this is a stress rating only and func tional operation of the device at th ese 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. the dallas semiconductor DS1720 is built to the highes t quality standards and manufactured for long term reliability. all dallas semiconductor device s are made using the same quality materials and manufacturing methods. however, the DS1720 is not expos ed to environmental stresses, such as burn?in, that some industrial applications require. for specific reliability information on this product, please contact the factory in dallas at (972) 371?4448. recommended dc operating conditions parameter symbol min typ max units notes supply v dd 2.7 5.5 v 1 logic 1 v ih 2.0 v cc +0.3 v 1 logic 0 v il -0.3 +0.6 v 1 dc electrical characteristics (-55 c to +125 c; v dd =2.7v to 5.5v) parameter symbol condition min max units notes thermometer error t err 0 c to 85 c -55 c to +125 c 2.5 c 10,11 logic 0 output v ol 0.4 v 3 logic 1 output v oh 2.4 v 2 input resistance r i rst to gnd dq, clk to v dd 2 2 m m active supply current i cc 0 c to +70 c 1 ma 4,5 standby supply current i stby 0 c to +70 c 1 a 4,5 single convert timing diagram (stand-alone mode) see typical curve DS1720 12 of 13 ac electrical characteristics (-55 c to +125 c; v dd =2.7v to 5.5v) parameter symbol min typ max units notes temperature conversion time t tc 400 1000 ms data to clk setup t dc 35 ns 6 clk to data hold t cdh 40 ns 6 clk to data delay t cdd 100 ns 6,7,8 clk low time t cl 285 ns 6 clk high time t ch 285 ns 6 clk frequency t clk dc 1.75 mhz 6 clk rise and fall t r, t f 500 ns rst to clk setup t cc 100 ns 6 clk to rst hold t cch 40 ns 6 rst inactive time t cwh 125 ns 6,9 clk high to i/o high-z t cdz 50 ns 6 rst low to i/o high-z t rdz 50 ns 6 convert pulse width t cnv 250 ns 500 ms nv write cycle time t wr 10 50 ms 12 ac electrical characteristics (-55 c to +125 c; v dd =2.7v to 5.5v) parameter symbol min typ max units notes input capacitance c i 5pf i/o capacitance c i/o 10 pf notes: 1. all voltages are referenced to ground. 2. logic one voltages are specified at a source current of 1 ma. 3. logic zero voltages are specified at a sink current of 4 ma. 4. i cc specified with dq pin open and clk pin at v dd . 5. i cc specified with v cc at 3.3v and rst =gnd. 6. measured at v ih = 2.0v or v il = 0.6v. 7. measured at v oh = 2.4v or v ol = 0.4v. 8. load capacitance = 50 pf. 9. t cwh must be 10 ms minimum following any write command that involves the e 2 memory. 10. see typical curve for specification limits outside 0c to 85c range. 11. thermometer error reflects temperature accuracy as tested during calibration. 12. writing to the nonvolatile memory should only take place in the 0c to 70c temperature range. DS1720 13 of 13 DS1720 typical thermometer error |
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