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I need to connect my PIC32 to an Allview Android tablet over USB so that the tablet will charge from my PIC board and also be able to communicate at the same time.

I can connect the PIC32 to a FT312D using the UART.

The FT312D seems to support AOA.

Page 15 of theFT312D datasheet shows an example application that appears to supply the tablet with +5V.

datasheet extras

https://www.ftdichip.com/Support/Documents/DataSheets/ICs/DS_FT312D.pdf

Is there any special setting or configuration I must do? Do I need an OTG cable? How does this work exactly?

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The picture that you provided and the datasheet shows that the tablet can be powered / charged from the module where the FTDI312 is, not charged from FTDI312 IC itself (BTW, FTDI312 uses 3.3V).

The image is an "application example", the FTDI312 is only the green box; other components (resistors, ferrite bead, capacitors) will be added to circuit by the user.

enter image description here

Be sure that the 5V power supply meets the requirements for charging the tablet (when charging from micro-USB, all three generic Android tablets that I've had drawed about 1000 mA; check yours). The supply has to power FT312D and probably PIC32, too.

This is not the situation where an OTG cable is needed. An OTG would be needed only if you wanted to power FTDI312 module FROM the tablet.

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  • \$\begingroup\$ Just hooked up a meter to an USB charger, seems mine draws about 200 mA. Maybe it's because it's already charged at 95%? \$\endgroup\$ – Nick M Sep 19 '20 at 11:53
  • \$\begingroup\$ Micro-USB connector is rated for a maximum of 1000mA. All the three generic tablets I've had observed this limit (data from manual; to be honest, I never measured it), and all of them nominally accepted 2A when charged through the thin barrel connector. Since the charging current is defined by the to-be-charged-device, and devices with Lithium rechargeables batts have charging-control ICs, it wouldn't be a surprise if the charge-control IC reduces the charging current when the battery's level approaches 100%. The only way to be sure is doing another measure when the battery is almost depleted. \$\endgroup\$ – mguima Sep 19 '20 at 18:45
  • \$\begingroup\$ I wonder what happens if the current is limited, eg 100 mA when it tries to draw some 400mA. \$\endgroup\$ – Nick M Sep 19 '20 at 19:08
  • \$\begingroup\$ If the available charging current is limited, the main consequence is that more time would be needed for charging the device. If a phone can be charged with its standard 1,500 mA charger, and it is connected to a 750 mA charger, it still charges, but takes more time to be fully charged. A charging battery and its charge-control IC doesn't act as a "resistive charge", in the sense that there is not a fixed resistance behaving by ohm's law. \$\endgroup\$ – mguima Sep 19 '20 at 20:56

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