SLUSCC7C July 2016 – June 2018 TPS546C23
An internal temperature sensor based off the bandgap reference protects the devices from thermal runaway. The internal thermal shutdown threshold, TSD, is fixed at 145°C (typical). When the devices sense a temperature above TSD, an otf_bg bit in the STATUS_MFR_SPECIFIC command is flagged, and power conversion stops until the sensed junction temperature decreases by the amount of the thermal shutdown hysteresis, THYST (20°C typical). The SMBALERT signal is triggered if it is not masked.
The devices also provide temperature telemetry and programmable internal overtemperature fault or warning thresholds using measurements from an internal temperature sensor as shown in Figure 33. The temperature-sensor circuit applies two bias currents to an internal diode-connected NPN transistor, and measures ΔVBE to infer the junction temperature of the sensor. The devices then digitize the result and compare it to the user-configured overtemperature fault and warning thresholds. When an internal overtemperature fault (OTF) is detected, power conversion stops until the sensed temperature decreases by 20°C. The READ_TEMPERATURE_1 (8Dh) register is continually updated with the digitized temperature measurement, enabling temperature telemetry. The OT_FAULT_LIMIT (4Fh) and OT_WARN_LIMIT (51h) commands set the overtemperature fault and warning thresholds through the PMBus interface. When an overtemperature event is detected, the device sets the appropriate flags in STATUS_TEMPERATURE (7Dh) command and triggers the SMBALERT signal if it is not masked.
The device response upon internal overtemperature fault can be set to Latch-off, Restart and Ignore in OT_FAULT_RESPONSE. The default response to an over temperature fault is to ignore. Fixed band gap-detected overtemperature (OT) faults are never ignored. The band gap OT faults always respond in a shutdown and attempted restart once the part cools. Table 2 summarizes the fault-response scheme.