7.3.5.3 Open-Circuit Detection

The TPS92611-Q1 device has LED open-circuit detection. Open-circuit detection monitors the output voltage when the channel is in the ON state. Open-circuit detection is only enabled when DIAGEN is HIGH. A short-to-battery fault is also detected as an LED open-circuit fault.

The device monitors dropout-voltage differences between the IN and OUT pins when PWM is HIGH. The voltage difference V_(IN) – V_(OUT) is compared with the internal reference voltage V_{(OPEN_th_rising)} to detect an LED open-circuit failure. If V_(IN) – V_(OUT) falls below the V_{(OPEN_th_rising)} voltage longer than the deglitch time of t_{(OPEN_deg)}, the device detects an open-circuit fault. Once an LED open-circuit failure is detected, the constant-current source pulls the fault bus down. During the deglitch time period, if V_(IN) – V_(OUT) rises above V_{(OPEN_th_falling)}, the deglitch timer is reset.

When the PWM input is in auto-retry, the device keeps the output ON to retry if the PWM input is HIGH; the device sources a small current I_(retry) from IN to OUT to retry when the PWM input is LOW. In either scenario, once a faulty channel recovers, the device resumes normal operation and releases the FAULT pulldown.