VIN is connected to VBUS without a diode

[iabdalkader]

VBUS and VIN are both connected to the LDO input, but only VBUS has a diode, if VIN is connected to a lower voltage power supply, say a battery, while USB is connected, current will flow into the battery possibly damaging it, a second diode on VIN making an OR function, could prevent that.

[iabdalkader]

you could also look into using a power management/multiplexer chip, like TPS2114/5 which can handle two power sources, and also has current limiting and inrush current limiting, this can save you some trouble in the future.

[dpgeorge]

A diode from VIN to the LDO would drop too much voltage (for eg a Lion battery). A PMIC is a good idea...

[iabdalkader]

you could use a Schottky diode, it has a very low voltage drop, for example I'm using one which drops about 300mV at 500mA (max USB current). Oh but right, for 3.7v it might be too much, if the board draws less than 500mA, the LDO will see 3.4v which should still work.

[dpgeorge]

I have a Schottky diode for the VUSB->VIN diode, which drops about 300mV at 300mA. But such a diode on VIN will drop too much for a Lion: you need about 3.5-3.6V minimum for the LDO to operate.

[iabdalkader]

yes you're right, that's probably why most boards have VIN > 4.0v, anyway, I thought it was worth mentioning.