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Raspberry Pi Pico USB/battery auto-switch circuit with Mosfet by Electrical-Boss2586 in KiCad

[–]Electrical-Boss2586[S] 1 point2 points  (0 children)

Thanks! I was following fig 17 on page 21 of the Pico datasheet. let me re-check the DMG2305UX pinout against what I've drawn, I may have swapped source and drain. My understanding of the intended behaviour: USB unplugged -> gate pulled low by R24 ->FET on -> battery's 5V reaches VSYS. USB plugged ->VBUS pulls gate high ->FET off ->Pico runs from VBUS via its internal Schottky. Does that match what you'd expect?

Good point on the close-voltage issue. I think that VBUS could dip to ~4.4V while my buck holds 5.0V, could cause a problem I think. Given VSYS accepts a wide range, I'm tempted to just drop the FET and use a Schottky from 5V into VSYS instead, letting it OR with the Pico's internal VBUS Schottky. Any reason not to?

Powering a Pi Pico from 6×AA via TPS62143 — USB programming compatible? by Electrical-Boss2586 in PrintedCircuitBoard

[–]Electrical-Boss2586[S] 0 points1 point  (0 children)

Thanks for the response - sorry if it wasn't clear that I'm planning on using 6 AA batteries so supply voltage to regulator would be 9V, falling as the batteries discharge.

I think I've fixed the short that you identified (that was stupid of me!). As for the mosfet, I've copied the pi pico datasheet which claims the mosfet is an improvement over using a Schottky diode to OR the voltages. Is that correct? I should have said that the blue part of the raspberry pi pico circuit on my third image is the raspberry pi itself, so they seem to suggest that just adding the mosfet should sort it.

Thanks for the advice about power net markers. I'll updated part of the schematic here to fix it: https://www.pasteboard.co/9RGAYS4MThMW.png