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BQ24251 Register #3 (USB_DET)

Rudy Garcia
Intellectual 380 points

When transitioning from Standalone to Host mode, will the USB_DET bits (Register #3 bits 1 and 0) contain the automatically detected status if read, or should I first perform a manual detection with the DPDM_EN bit (Register #5 bit 4) before reading them? Part 2 of this question has to do with how long it takes for DPDM_EN to be cleared by the charger once it is set by software. It takes quite a long time (seconds) for this bit to be cleared when there is no VBUS (no USB cable is plugged in). When VBUS is present (USB cable is plugged in) the DPDM_EN bit is cleared very quickly (less than 1 second). Is this because there is a D+/D- timer that is actively waiting for an attachment event?

  • 0
    TI__Guru**** 166996 points
    The USB_DET bits retain the detected status. Forcing a manual detection does not complete (i.e., the status will not change and the bit will not clear) if the current status DCP, SDP with weak battery or CDP with weak battery. DCD can take up to 900ms, primary detection up to 400ms and secondary detection up to 400ms so I recommend waiting at least 2 seconds. There is no timer. Force detection when V(IN) is below UVLO is not reliable.