The TMP118 has a temperature comparator feature that uses the THigh_Limit register for high temperature comparator threshold and the TLow_Limit register for low temperature comparator threshold. The low temperature comparator threshold is used to program the comparator hysteresis. The comparator thresholds are programmed in the TMP118 in a 16-bit two's complement format and with a resolution of 7.8125m°C. The Alert_Flag bit in the Configuration register is asserted when the temperature result equals or exceeds the THigh_Limit for a consecutive number of conversions as set by the Fault bits in the Configuration Register, which can be programmed to 1, 2, 4, or 6 consecutive conversions. The Alert_Flag clears when the temperature result drops below the TLow_Limit for the same consecutive number of conversions. The difference between the two limits acts as a hysteresis on the comparator output, and the fault counter prevents false alerts as a result of environmental temperature fluctuations. The Alert_Flag can be programmed to active low or active high by configuring the Polarity bit in the Configuration Register.

As shown in Figure 7-5, the alert status becomes active when the temperature equals or exceeds the value in THigh_Limit for Fault number of consecutive conversions. The alert status remains active until the temperature falls below the TLow_Limit for the same number of consecutive conversions. The Alert_Flag can also be cleared by issuing the General Call Reset command.

Figure 7-5 Alert_Flag Behavior