SLUUCY8 December 2023 BQ77307
The BQ77307 device integrates an Overtemperature in Discharge (OTD) Protection that compares the voltage of an external negative temperature coefficient (NTC) thermistor on the TS pin to a programmable threshold VOTD, and triggers an alert or fault if the voltage is less than the threshold. The thermistor is biased using an on-chip 20-kΩ pullup resistor (which is trimmed in TI factory), which is biased by the internal 1.8 V LDO (VREG18) rail only when the thermistor is being evaluated (which is the default recommended setting). Alternatively, the pullup resistor can be biased continuously by sending the 0x69 REGOUT_CONTROL() command with the [TS_ON] bit set. The detection circuitry uses this same internal 1.8 V LDO rail to generate the detection threshold, thereby implementing a ratiometric comparison.
The VOTD threshold is programmable in units of VREG18 / 359, with settings from 0 to 255 using the Protections:Temperature:Overtemperature in Discharge Protection Threshold configuration register. The OTD protection is enabled using the Settings:Protection:Enabled Protections B:[OTD] configuration bit.
The OTD protection triggers an alert signal when an overtemperature in charge event is first detected, then triggers a fault if this persists after a programmable number of CHECK intervals, OTD_DLY, which can be set from 0 to 255. The delay is set by the Protections:Temperature:Overtemperature in Discharge Protection Delay configuration register.
When an OTD fault is triggered, the device turns off the DSG FET if configured for autonomous FET control, based on the setting in Settings:Protection:DSG FET Protections A[OTD]. The device recovers when the thermistor voltage is detected greater than or equal to the threshold set by Protections:Temperature:Overtemperature in Discharge Protection Recovery (which has the same threshold range from 0 to 255 in steps of VREG18 / 359). If the Protections:Temperature:Overtemperature in Discharge Protection Recovery is set to zero, autonomous recovery is disabled, and recovery must be initiated by the host sending the PROT_RECOVERY() subcommand with the [TEMPREC] bit set.
| Status | Condition | Action |
|---|---|---|
| Normal | TS pin voltage ≥ Protections:Temperature:Overtemperature in Discharge Protection Threshold | Safety Alert B()[OTD] = 0 |
| Alert | TS pin voltage < Protections:Temperature:Overtemperature in Discharge Protection Threshold | Safety Alert B()[OTD] = 1 |
| Trip | TS pin voltage < Protections:Temperature:Overtemperature in Discharge Protection
Threshold for Protections:Temperature:Overtemperature in Discharge Protection Delay duration | Safety Alert B()[OTD] = 0 Safety Status B()[OTD] = 1 and DSG FET can be disabled depending on settings |
| Recovery | Safety Status B()[OTD] = 1 and TS pin voltage ≥ Protections:Temperature:Overtemperature in Discharge Protection Recovery | Safety Status B()[OTD] = 0 and DSG FET can be re-enabled based on settings |