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Pi Pico W datasheet states:

3V3_EN connects to the on-board SMPS enable pin, and is pulled high (to VSYS) via a 100kΩ resistor. To disable the 3.3V (which also de-powers the RP2040), short this pin low.

and

RUN is the RP2040 enable pin, and has an internal (on-chip) pull-up resistor to 3.3V of about ~50kΩ. To reset RP2040, short this pin low.

Which means that RUN resets the microcontroller and 3V3_EN powers it off. Practically (in application) both sound to me as they will only reset the microcontroller. I tried also using both pins and haven't noticed any difference in the behavior: microcontroller starts over, once the pin is released (i.e. pulled up again).

So, the question is, what is the practical difference between using RUN pin or 3V3_EN in applications?

Vadim
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4 Answers4

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One difference is that you can detect whether the last reset occurred due to the power supply (eg. 3V3_EN), the RUN pin, or via the Rescue Debug Port, by checking the CHIP_RESET register.

See section 2.12.7. Source of Last Reset in the RP2040 Datasheet.

Deltabeard
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  • Shortening the RUN pin to ground resets only the RP2040 microcontroller.
  • Shortening the 3V3_EN pin to ground disables the Pico's RT6150B-33GQW 3V3 internal voltage regulator. This effectively powers down (resets) the Pico and all external circuits powered by Pico's 3V3 pin. It may be handy if you power your project through Pico's USB connector while developing and debugging. Shortening 3V3_EN to the ground causes much less mechanical stress on the Pico's USB connector than constantly plugging in and out the USB cable.
Damir
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Presumably the 3V3_EN pin would result in a lower power suspend state as you're also shutting down the SMPS, which would make batteries last longer than doing the same thing with the RUN pin. It would be interesting to compare this with the internal SLEEP and DORMANT states you can enter via software.

As you mentioned in a comment, 3V3_EN will also shut down any external devices connected to the 3.3V line as well.

Presumably there will be a very slightly longer delay powering up from 3V3_EN as the SMPS has to start up before the RP2040 does, whereas the RUN pin should result in immediate reset of the RP2040 as the SMPS is already operating normally. However this delay would be tiny.

Malvineous
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Another practical consideration is that if you are using this feature a lot it is probably better to use reset rather than continuously cycle the power. Cycling the power a lot will stress it, shortening the life of the chip.

Dave Atkins
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