Turn off DCDC, and keep Witty powered by ~Vin (2.5 to 3.6V)?

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Last Post by uugear 2 days ago

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Matt Schneider

(@matt-schneider)

Posts: 3

Active Member Customer

Topic starter

Hello, to power the pi a 5V source is needed. But when the pi is off, is there an alternative, lower voltage, that can keep Witty Pi 4 Mini powered? For instance, if one used an external DCDC converter (or soldered to Witty) with an Enable pin, the DCDC could be kept OFF when the pi was down (then turned back on when the pi was about to be turned on). During this time, Witty could stay powered via a lower voltage on Vin - maybe? Looking for a way to not have the larger quiescent current of the DCDC when the pi is off.

The Witty Pi 4 L3V7 looks to have a pretty low quiescent current of ~0.3mA when battery powered, but the bummer is that it only services LiIon/Polymer, and not LFP (which our project is using).

Posted : 31/03/2025 6:23 am

uugear

(@admin)

Posts: 574

Member Admin

The main problem is: the 3.3V LDO that powers the ATtiny841 MCU, is connected to 5V rails instead of VIN rails. Although VIN connects to ATtiny841's ADC via a voltage dividing network (so VIN is measuable), it doesn't power the MCU.

A more feasible solution is to choose a DC/DC that has really low quiescent current, so it always outputs 5V and powers the MCU. This is the way how Witty Pi 4 (full sized) works.

Posted : 31/03/2025 7:41 am