What power supplies are required on the MAX32600 power pins?

The one required power supply for digital operation is VDD with a minimum of 1.8V, but if any of the analog circuitry is required without USB power then VDD must be a minimum of 2.3V. The VRTC rail is supplied by a 3V super-cap or battery directly on the pin and is necessary for backup to save critical data and power sequencer data in the event of main power loss (VDD or USB). Further, VRTC can be trickle-charged from the VDD or USB supplies. In order to use the GPIO's the VDDIO pin must be powered from an external source. The VDDA3ADC, VDDA3DAC, and VDDA3REF inputs should be externally connected to the analog VDDA3 source if analog circuitry is required. 

When USB power is present, the 3.3V LDO will use it to generate the VDDB rail from which many other rails will automatically switch to being powered from including VDDIO, VREG18, and VDDA3.