USB BiPower OTG Flex Module

I was afraid the MAX3353 might be NRND. Maxim doesn't make it too clear, but it was cut recently. For USB OTG to be supported long term, I'll need to swap in something like the STOTG04E. This may be a tough fit. I'll see what I can do, but it adds UART or i2c bridging support. I need to research D+/D- orientation. It may require changing out the USB connector and/or the TSU6721. The power supplies run well, I just need to pick a solution that doesn't get NRND'ed the second I finish the board.

While working on this board, I believe I should make a version that provides a USB bridge such as a i2c or UART to USB bridge. This depends on space available. Also, I believe the STM32 Large Flex Module may be able to include a version of this schematic.

Been working on other projects, even ones dependent on this board :). Anyway, I finally made one correctly after an additional issue with updating copper pours. The new design should support full current quite well and tests out OK. There is one 'smart' charger that shuts down after 30 seconds or so, but other power banks seem to work with it quite well without control logic. I need to figure out what is triggering the shutdown, hopefully nothing architectural. The design should just work with or without i2c management.

Feel pretty derpy. I just was populating these boards last night (I had a cold which has slowed me down by a week). The ESD/choke coil pattern was elongated. I think I never put one side's dimensions in and it just sort of looked right. Anyway, I fixed it and the bonus is a small improvement in routing, especially on the optional OTG charge pump/negotiator. I'll get them back in a couple of weeks to test again...

I have been working with TI on adding in optional charger support. Ideally, this module can run independent of a microcontroller or a charger. If it is standalone, it will do a BCD1.2 compatible check for a USB charging source to harness power. I believe I can also support OTG and if you have been watching our github, you will see some initial schematics. I'll be working with some new chips that are i2c based, but should cost similar and still work standalone. Providing OTG power support is pretty rare, so I think it will be an interested feature. In addition, there will be significantly improved filtering.

We are swapping parts.  Instead of the TPS62067, we are utilizing the TPS62086 buck converter for an increased current capability of 3A.  In addition, we are utilizing a LM2663MX instead of the TPS60401 to increase the -3.3V rail to 200mA.