I am validating backlight driver performance in regards to a short on the output and it is not behaving as expected. The test case assumes the positive output (VOUT) is shorted to the negative output (OUT1-4).
What we expect:
1) We short VOUT to OUT1-4.
2) OUT1-4 voltage begins to rise to VOUT level.
3) A Shorted LED FAULT is triggered.
4) Backlight driver recovers once EN pin is toggled.
What we see:
1) We short VOUT to OUT1-4.
2) OUT1-4 begins to rise to VOUT level.
3) FAULT pin is NOT triggered and OUT1-4 rises fully to VOUT.
4) VOUT and OUT1-4 decay to VIN levels (Switching stops).
5) Backlight driver recovers once EN pin is toggled.
The datasheet describes a shorted LED fault as:
“Detected if the voltage of one or more current sinks is above shorted string detection level and at least one OUTx voltage is within headroom window.”
In our case, we only have 1 LED string so there is no “voltage within headroom window”. I do not see any description for this scenario so are you able to shed some light on it? Our main concern is that the fault pin is not triggering, which makes us worry that the backlight driver does not see this as a failed state.
-Dave
