The ADT14 is a temperature sensor and controller that generates
an output voltage proportional to temperature and provides four
temperature trip points. The four trip points, or temperature
setpoints, and their hysteresis are determined by voltage levels set
by the user. An on-chip voltage reference provides an easy method
for setting the temperature trip points.
The ADT14 consists of a bandgap voltage reference combined
with four matched comparators. The reference provides both a
temperature-stable 2.5 V output, and a voltage proportional to
absolute temperature (VPTAT) which has a precise temperature
coefficient of 5 mV/K = 5 mV/(°C +273.15). The VPTAT output
is nominally 1.49 V at +25°C. The comparators determine
whether the VPTAT output is above the voltages set up by
external resistive dividers (temperature trip points) and generate
an open-collector output signal when one of their respective
thresholds has been exceeded.
Hysteresis is programmed by a user-selected voltage at the hysteresis
pin. This voltage adjusts the hysteresis current which is
used to generate a hysteresis offset voltage. The comparator’s
noninverting inputs are connected in parallel, which guarantees
that there is no hysteresis overlap and eliminates erratic transitions
between adjacent trip zones.
Using a proprietary thin-film resistor process in conjunction
with production laser trimming, a temperature accuracy of ±3°C
at 25°C is guaranteed. The open-collector outputs are capable
of sinking 5 mA, and provide TTL/CMOS logic compatibility
with an external pull-up resistor. Operating from a single 5 V
supply, the quiescent current is 600 mA max.
The ADT14 is available in the 16-lead epoxy DIP and SO
(small outline) packages.