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I have designed a product (small
FT234XD usb-to-uart bridge and it connects to any mobile phone via
USB cable (
90mA maximum current). My device acts as
USB slave and can connect to any mobile phone which supports
OTG. However, we are facing one problem. We are selling our product with
lenovo tablet and user won't be able to disconnect the device and charge the tablet regularly.
I came across several links stating that most of the
usb hardware in mobile phones and tablets have a mode in which mobile/tablet can act as
USB master and still charge itself at the same time. So, we have tried several resistors across
ID pin and ground of the usb connector but tablet either charge only or it detects the device.
Finally, I am considering one
FT311D chips which may work for us but I am not sure if it will be possible with it. Can anyone help me with this problem? Should we try other things with existing hardware (FT234XD) or try this new
My Tablet is
Lenovo Tab 3 Essential Tablet. I am planning to try
FT312D. Good news is that my team ran few software tests and get to know Tab software supports
Android usb accessory mode. In this mode,
FT312D will be the host and I think I can charge the tab and communicate with it. I think It will work because
tab will be in slave mode and can charge itself while communicating with my device and only thing required support of accessory mode in software. Am I correct?
My device has
PIC24E 16-Bit microcontroller. There is no USB Protocol specific firmware in PIC24EP. PIC24EP just communicates with mobile application using string based commands. PIC sends commands over
UART and FT234XD converts them to USB. Commands received from Android application is converted to commands over UART and is returned to PIC. So, I think changing USB part of my device doesn't require any change in firmware of my primary microcontroller.