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BQ500511A: FOD tripping but disabled

Part Number: BQ500511A
Other Parts Discussed in Thread: BQ51003, BQ50002A

Hi,

We are using the BQ500511A in combination with the BQ50002A for a wireless charger in combination with the BQ51003 on the receiver side. We noticed a strange error state which can be triggered by slowly removing the RX from the TX. We have LED mode 4 (Rled = 66.5kOhm) and in the mentioned state, the LED B is constant on for 5 minutes. According to the datasheet (if I understand it correctly), the 5 minute fault indication could be due to overtemperature of the receiver, overtemperature detected through the NTC on the charger, or FOD trip. However, I am almost certain that the error could not be temperature related since I left the devices to cool before triggering this state, and it should also not be FOD tripping since we disabled FOD by tying FOD_THR to 3V.

I was wondering if there are other cases where there is a fault that triggers a 5 minute indication on the LED, or if it is possible that an EPT-3, NTC or FOD trip is falsely communicated/received?

Some extra observations: sometime when I try to trigger this error state, I also see LED_B blinking fast. Following the dataseet with LED mode 4, this should indicate FOD warning, but as I mentioned we should have disabled FOD detection. Am I missing something that could still trigger FOD with FOD_THR tied to 3V?

Best regards,

Wout