SLIS178B October 2017 – January 2018 TPS92830-Q1
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.