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BQ24257 D+ / D- in parallel with USB bridge device

Allen Stuart
Prodigy 240 points
Other Parts Discussed in Thread: BQ24257

Hello,

I currently have a design that requires USB to I2C translation, but also charges a lithium polymer cell. I would like to know if the charger port detection mechanism would cause issues with the enumeration of another USB device when in parallel with the D+/D- lines.  I haven't seen any data relating to not doing this.  However I have seen devices that utilise a switch in the D+/D- lines for secondary detection.

Any help would be appreciated,

Thanks.

  • 0
    TI__Expert 7730 points
    Yes you can have other USB device connected in parallel. It will only take up to 800ms for the charger to finish the USB detection after the input adapter is plugged in. The USB lines will be released after the detection is done and can be used for enumeration.

    thanks,
    Wenjia
  • 0 in reply to Wenjia Liu
    Prodigy 240 points
    Hi Wenjia,

    Thank you for your prompt reply, does this mean in the 800ms there is potential for device conflict? I had thought initially that the BQ24257 would have had high input impedance to detect the port type. If this is not the case I would imagine it best practice to prevent the USB to I2C device from enumerating in the first 1000ms of USB supply detection.

    Kind regards,
    Allen
  • 0 in reply to Allen Stuart
    TI__Expert 7730 points
    Yes it will be safer if you wait 1 second till the detection is finished to start the enumeration.

    Thanks,
    Wenjia