DS1620 Datasheet, PDF (2/13 Pages) Dallas Semiconductor – Digital Thermometer and Thermostat

DS1620
User–defined 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 DS1620 over a simple 3–wire interface.
OPERATION-MEASURING TEMPERATURE
A block diagram of the DS1620 is shown in Figure 1. The DS1620 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 DS1620 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 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 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-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.
DS1620 FUNCTIONAL BLOCK DIAGRAM Figure 1
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