AUX_5V is generated by a 600mA boost DC/DC converter. As this converter powers USB devices connected to J47 and J48 - if any - and DWM WiFi/Bluetooth module (if populated), maximum current available at connector J54 can not be provided.
In case additional circuitry has to interfaced to processor's I/Os , '''proper power sequencing
must be implemented''' in order to avoid back power phenomena. To do that, AUX_3.3V should be used:
* additional circuitry can be powered by AUX_3.3V directly
*AUX_3.3V can be used as enable signal to power-up this circuitry.