Guru
Joined: 05/10/2019
Location: United KingdomPosts: 8885
| Posted: 07:25am 16 May 2026 |
The on-board regulator on the Zero can provide a max of about 100mA (in addition to powering the RP2040). I usually keep it under that as the heatsink (the USB connector) isn't brilliant. If you keep within its limit things run cool, in my experience.
Do pay particular attention to the point I made about the USB supply NOT being isolated by a diode from the 5V pin though! You can damage some PCs by having this pin on a 5V supply while the USB lead is connected.
I would suggest:
Power the Pico at 5V.
Do not connect the 5V pin on the Zero.
Link the GND and 3V3 pins on the two modules together, with the 3V3 via a jumper.
Connect the I2C pullup resistors to the 3V3 supply from the Pico.
Ideally the 3V3 from the Pico should have a diode to the 3V3 pin on the Zero rather than a jumper but that's introducing too much volt drop to be safe. The jumper allows you to program the Zero without powering the Pico and anything else attached to its 3V3.
It would really be better to use a 5V to 3V3 switcher and power both modules from that at 3V3. Disable the 3V3 reg on the Pico and don't connect the 5V, VBUS or VSYS pins. Something like the SO6 module is very cheap and can provide a solid 500mA, but any small buck regulator will do. This has several advantages. It reduces noise pick-up on the supply rail, reduces 3V3 rail impedance to reduce switching spikes and makes the power supply more flexible - you could power it with anything between 5V and 12V, smooth or not.