The TPS929121-Q1 has internal analog comparators to monitor all channel outputs with respect to a fixed threshold. If the device has detected channel voltage below threshold, it sets FLAG_SHORTCHx accordingly. The FLAG_OUT and FLAG_ERR are set as well.

The short-circuit detection is only enabled during PWM-ON state with programmable minimal pulse width of T_(ODPW) + T_{(SHORT_deg)}. The T_(ODPW) is programmable by register CONF_ODPW. If PWM on-time is less than T_(ODPW) + T_{(SHORT_deg)}, the device cannot report any short-circuit fault. When the voltage V_(OUTx) is below threshold V_{(SG_th_rising)} with duration longer than deglitch timer length of T_(ODPW) + T_{(SHORT_deg)}, the device turns off the current output on the LED short-circuit channels, pulls the ERR pin down with constant current sink to report fault, and sets flag registers including FLAG_SHORTCHx, FLAG_OUT and FLAG_ERR. If any channel is disabled by CONF_ENCHx to 0, the LED short-circuit diagnostics skip the channel. If one-fails-all-fail protection is enabled by setting EEPROM register EEP_OFAF to 1, all the used output channels are turned off even though the LED short-circuit is only detected on one channel. If one-fails-all-fail protection is disabled by setting EEPROM register EEP_OFAF to 0, only failed channels are turned off.

In fail-safe states, the TPS929121-Q1 retries the failed channel with a low-current retry pulses in every 10 ms. The pulse width T_(ODPW) is programmable by CONF_ODPW, and the retry current is set by CONF_ODIOUT. If the retry is succeed, the device turns on the channel current, automatically release the ERR pin and clears the flag registers. If the CONF_DIAGENCHx is set to 0, the short-circuit fault is ignored.

Possible user case:

1. Supply voltage dip below threshold, triggering false single led short-circuit fault
2. LED short to ground and recover
3. LED single LED short and recover
4. Dutycycle too short to detect
5. Extra capacitance caused false short-circuit