8.3.7 THERM and ALERT/THERM2

The TMP43x have two pins dedicated to alarm functions, the THERM and ALERT/THERM2 pins. Both pins are open-drain outputs that each require a pullup resistor to V+. These pins can be wire-ORed together with other alarm pins for system monitoring of multiple sensors. The THERM pin provides a thermal interrupt that cannot be software disabled. The ALERT pin is intended for use as an earlier warning interrupt, and can be software disabled, or masked. The ALERT/THERM2 pin can also be configured for use as THERM2, a second THERM pin (Configuration Register 1: AL/TH bit = 1). The default setting configures pin 6 for the TMP431 and pin 8 for the TMP432 to function as ALERT (AL/TH = 0).

The THERM pin asserts low when either the measured local or remote temperature is outside of the temperature range programmed in the corresponding Local/Remote THERM Limit Register. The THERM temperature limit range can be programmed with a wider range than that of the limit registers, which allows ALERT to provide an earlier warning than THERM. The THERM alarm resets automatically when the measured temperature returns to within the THERM temperature limit range minus the hysteresis value stored in the THERM Hysteresis Register. The allowable values of hysteresis are listed in Table 13. The default hysteresis is 10°C. When the ALERT/THERM2 pin is configured as a second thermal alarm (Configuration Register: bit 7 = x, bit 5 = 1), it functions the same as THERM, but uses the temperatures stored in the Local/Remote Temperature High Limit Registers to set its comparison range.

When ALERT/THERM2 is configured as ALERT (Configuration Register 1: bit 7 = 0, bit 5 = 0), the pin asserts low when either the measured local or remote temperature violates the range limit set by the corresponding Local/Remote Temperature High/Low Limit Registers. This alert function can be configured to assert only if the range is violated a specified number of consecutive times (1, 2, 3, or 4). The consecutive violation limit is set in the Consecutive Alert Register. False alerts that occur as a result of environmental noise can be prevented by requiring consecutive faults. ALERT also asserts low if the remote temperature sensor is open-circuit. When the MASK function is enabled (Configuration Register 1: bit 7 = 1), ALERT is disabled (that is, masked). ALERT resets when the master reads the device address, as long as the condition that caused the alert no longer persists, and the Status Register has been reset.