8.3.7.3 LED Open-Circuit Detection

The TPS92830-Q1 device has channel-independent LED open-circuit detection. Once an LED open-circuit failure is detected, the device turns off the faulty channel and retries automatically. If the retry mechanism detects that the LED open-circuit fault is removed, the device resumes normal operation.

The device monitors MOSFET dropout voltage differences between the ISNx and SENSEx pins. Voltage difference V_(ISNx) – V_(SENSEx) is compared with internal reference voltage V_{(OPEN_th_rising)} to detect an LED open-circuit failure. If V_(ISNx) – V_(SENSEx) falls below the V_{(OPEN_th_rising)} voltage and it stays there longer than the deglitch time of t_{(OPEN_deg)}, the device asserts an open-load fault on this channel. During the deglitching time period, if V_(ISNx) – V_(SENSEx) rises above V_{(OPEN_th_falling)}, the deglitch timer is reset.

In normal operation, the N-channel MOSFET operates in the saturation region with a gate-source voltage close to its threshold voltage. In this case, the drain-source voltage of the N-channel MOSFET is typically much higher than open-circuit threshold V_{(OPEN_th_rising)}. In the LED open-circuit condition, the N-channel MOSFET operates in the linear region with a gate-source voltage much higher than its threshold voltage. The N-channel MOSFET is fully on.

If a fault is detected, a constant-current source pulls the fault bus down. If the FAULT pin is low, all devices connected to the fault bus are off in the fault mode.