@SmashedTransistors Ahhh, those clever americans! The USB host on the T4.1 is powered through a TPD3S014 (a current limit switch) and the enable is controlled by the MCU. It does everything you need, over and reverse current, and discharge. Brilliant.
(Aside, what is the minumum code to turn the usb host on and off?)
The drawback is that the TPD3S014 is powered after the 0.5A fuse (see schematic below). So total draw is 0.5A including the T4.1 (100mA ?) and whatever is powered by its 3.3V LDO (a TLV75733P, 1A). I think that leaves 400mA for all of the peripherals (5V and 3.3V) together. (*)
But, there is still the nagging question about what happens wrt digital i/o connections when one thing or the other is powered up first.
@PaulStoffregen , help, please?
1) On quick perousal of the Processor Reference Manual, it looks like the GPIO pins are initially tri-stated. Is that correct?
2) Does that change during the power up sequence?
3) What is the state of the digital i/o pins when a user sketch enters setup()?
Apologies if you have documented this somewhere, I have not found it.
Thank you
For those who don't have the schematic at their finger tips, here it is. Notice the TPD3S014, it runs from the USB after the fuse and filter. So, max is still 500mA including the MCU and whatever else is driven from the 3.3V LDO
(*) If someone needs more that 400mA, perhas the TPS214/5x (0.6A) or TPS25221 (adjustable up to 2.7A) might work, though I have no idea what vin on the t4.1 could accomodate).