The MAX6691 four-channel thermistor temperature-to-pulse-width converter measures the temperatures of up
to four thermistors and converts them to a series of output
pulses whose widths are related to the thermistors'
temperatures. Each of the four thermistors and an
external fixed resistor (REXT) form a voltage-divider that
is driven by the MAX6691's internal voltage reference
(VREF). VREF and the voltage across REXT are measured and converted to a pulse.
The MAX6691 has a single open-drain I/O pin that can
be readily connected to a variety of microcontrollers.
The microcontroller initiates a conversion by pulling the
I/O pin low and releasing it. When conversion is done,
the MAX6691 signals the end of conversion by pulling
the I/O pin low once again. The pulse corresponding to
the first thermistor is sent immediately after the release
of the I/O pin.
The on-chip power-management circuitry reduces the
average thermistor current to minimize errors due to
thermistor self-heating. Between conversions, the
MAX6691 falls into a 10µA (max) sleep mode, where
the voltage reference is disabled and the supply current
is at its minimum.
The MAX6691 is available in a 10-pin µMAX package
and is specified from -55°C to +125°C temperature
range.
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