Owner manual

DS1720

030598 2/12

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 measurement

technique. A block diagram of the temperature mea-

surement circuitry is shown in Figure 2.

The DS1720 measures temperature by counting the

number of clock cycles that an oscillator with a low tem-

perature coefficient goes through during a gate period

determined by a high temperature coefficient oscillator.

The counter is preset with a base count that corre-

sponds to –55°C. If the counter reaches zero before the

gate period is over, the temperature register, which is

also preset to the –55°C value, is incremented, indicat-

ing 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 cir-

cuitry is needed to compensate for the parabolic behav-

ior 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 neces-

sary 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 accumu-

lator) at a given temperature must be known.

DS1720 FUNCTIONAL BLOCK DIAGRAM Figure 1

RST

ADDRESS

AND

RESET

CLK

STATUS REGISTER AND

CONTROL LOGIC

TEMPERATURE SENSOR

HIGH TEMP TRIGGER, TH

LOW TEMP TRIGGER, TL

DIGITAL COMPARATOR/LOGIC

HIGH

LOW

COM