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.
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