The TPS929121-Q1 integrates LED open-circuit diagnostics to allow users to monitor LED status real time. The device monitors voltage difference between SUPPLY and OUTx to judge if there is any open-circuit failure. The SUPPLY voltage is also monitored by on-chip ADC with programmable threshold to determine if supply voltage is high enough for open-circuit diagnostics.

The open-circuit monitor is only enabled during PWM-ON state with programmable minimal pulse width greater than T_(ODPW) + T_{(OPEN_deg)}. The T_(ODPW) is programmed by register CONF_ODPW. If PWM on-time is less than T_(ODPW) + T_{(OPEN_deg)}, the device does not report any open-circuit fault.

When the voltage difference V_(SUPPLY) – V_(OUTx) is below threshold V_{(OPEN_th_rising)} with duration longer than T_(ODPW) + T_{(OPEN_deg)}, and the device supply voltage V_(SUPPLY) is above the threshold V_{(ADCLOWSUPTH)} set by register CONF_ADCLOWSUPTH, the TPS929121-Q1 pulls the ERR pin down with one pulsed current sink for 50 µs to report fault and set flag registers including FLAG_OPENCHx, FLAG_OUT and FLAG_ERR to 1. If the device supply voltage V_(SUPPLY) is below the threshold V_{(ADCLOWSUPTH)} set by register CONF_ADCLOWSUPTH, open-circuit fault is not detected nor reported.

Once the open-circuit failure is removed, the master controller must write 1 to CLR_FAULT to reset fault flags.