DS1720 ECON-Digital Thermometer and Thermostat www.maxim-ic.com FEATURES PIN ASSIGNMENT Requires no external components Supply voltage range covers from 2.7V to V DQ 1 8 DD 5.5V 2 7 CLK/CONV T HIGH Measures temperatures from 55C to RST 3 6 T LOW +125C in 0. 5C increments. Fahrenheit 4 5 T GND COM equivalent is 67F to +25 7F in 0. 9F DS1720S 8-Pin SOIC (208-mil) increments Temperature is read as a 9bit value Converts temperature to digital word in 1 second (max) Thermostatic settings are userdefinable and nonvolatile PIN DESCRIPTION Data is read from/written via a 3wire serial DQ 3Wire Input/Output interface (CLK, DQ, RST ) CLK/ CONV 3Wire Clock Input and Applications include thermostatic controls, Standalone industrial systems, consumer products, Convert Input thermometers, or any thermally sensitive RST 3Wire Reset Input system GND Ground 8pin SOIC (208 mil) package T High Temperature Trigger HIGH T Low Temperature Trigger LOW T High/Low Combination Trigger COM V Power Supply Voltage (3V-5V) DD DESCRIPTION The DS1720 Digital Thermometer and Thermostat provides 9bit temperature readings which indicate the temperature of the device. With three thermal alarm out-puts, the DS1720 can also act as a thermostat. T is driven high if the DS1720s temperature is greater than or equal to a userdefined temperature HIGH T . T is driven high if the DS1720s temperature is less than or equal to a userdefined temperature H LOW T . T is driven high when the temperature exceeds T and stays high until the temperature falls below L COM H that of TL. Userdefined temperature settings are stored in nonvolatile memory, so parts can be programmed prior to insertion in a system, as well as used in standalone applications without a CPU. Temperature settings and temperature readings are all communicated to/from the DS1720 over a simple 3wire interface. 1 of 14 020106 DS1720 ORDER INFORMATION ORDERING PACKAGE DESCRIPTION NUMBER MARKING DS1720S+ DS1720 (see note) DS1720 in Lead-Free 208mil 8-pin SO DS1720S+T&R DS1720 (see note) DS1720 in Lead-Free 208mil 8-pin SO, 2500 Piece Tape-and-Reel DS1720S DS1720 DS1720 in 208mil 8-pin SO DS1720S/T&R DS1720 DS1720 in 208mil 8-pin SO, 2500 Piece Tape-and-Reel Note: A + symbol will also be marked on the package near the Pin 1 indicator. OPERATIONMEASURING TEMPERATURE A block diagram of the DS1720 is shown in Figure 1. The DS1720 measures temperatures through the use of an onboard proprietary temperature measurement 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 with a base count that corresponds to 5 5C. If the counter reaches zero before the gate period is over, the temperature register, which is also preset to the 55C value, is incremented, indicating that the temperature is higher than 55C. 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 counter 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 resolution temperature measurement. This is done by changing the number of counts necessary for the counter to go through for each incremental degree in temperature. To obtain the desired resolution, therefore, both the value of the counter and the number of counts per degree C (the value of the slope accumulator) at a given temperature must be known. 2 of 14