Four-Channel Thermistor Temperature-to-Pulse-Width Converter

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.

Applications

* Home Appliances * HVAC * Medical Devices

* Simple Single-Wire Interface

* Measures Up to Four Thermistor Temperatures

* Low-Average Thermistor Current Minimizes Self-Heating Errors

* Internal Voltage Reference Isolates Thermistor from Power-Supply Noise

* Accommodates Any Thermistor Temperature Range