3V3 External Power Supply + USB_STLK for debugging on NUCLEO-WL55JC1

[lame_stmr]

Hello,

Is it possible to power this board with an external 3.3 volt supply while still having the st-link active for debugging purposes? If not, how else can I debug my firmware? I've looked through the UM2592 for the dev board, but can't seem to nail down my answer. Any advice is appreciated. Thank you.

[TDK]

All of the supported power options are 5 V, not 3.3 V. That's how the st-link chip gets power.

But sure, it's possible. Both the st-link chip and the target chip need powered, and the grounds need to be tied. Dig into the schematic for ways to tie 3V3_STLK to your 3.3V supply.

[lame_stmr]

Thank you for the quick reply.

Yes, from a schematic standpoint I can see how to do it. However, I'd like to clarify the 3 voltage inputs to the ST-Link in the NUCLEO-stm32wL power tree. There is 3V3_STLK, 5V PWR, and 3V3 (my supply). If I leave 5V PWR disconnected by removing jumpers on JP4 and JP7, I believe 3V3_STLK would still be active as LDO U7 is hard-wired to the 5V usb input, so then why is it that the STLK is not active if as you said it just needs 3V3 STLK? Sorry if im being *** i just want to confirm so i can move on. I attached an image with some quick notes on the power tree. Thank you.

[TDK]

The "3V3" net does not power the st-link. It is powered from 3V3_STLK. Look at the schematic:

[lame_stmr]

Noted, isn't 3V3_STLK high though as soon as USB is plugged in? So should the STLK be available? Looking at this attached image.

[TDK · Accepted solution]

Yes, 3V3_STLK will be powered if USB is connected (via 5V_USB_CHGR).

[lame_stmr]

Okay, so, last question (hopefully).

if i follow this configuration:

1. Connect my own 3V3 supply on CN6 pin 4

2. Remove jumpers on JP4 and JP7 to disconnect the "5V_PWR" from ST-Link

2. Connect USB power and U7 LDO regulates the 3V3_STLK to high.

4. Will this result in me being able to separately power the STM32WL MCU and still be able to have USB plugged in to keep ST-Link on and read/debug fw logs?

I know I could just test it myself but I don't have the board with me right now and want to check beforehand. Let me know. Thanks again!

[Andrew Neil]

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@lame_stmr wrote:

If not, how else can I debug my firmware?

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The easiest way is to just take power from the ST-Link's USB.

That's the "normal" way to power the board - everything running from the USB connection of the ST-Link.

What's your particular reason for needing a separate power supply?

[lame_stmr]

Nothing crazy. I just wanted to quickly try battery power regulated to 3.3 volt to power the whole MCU part and then only use the usb connection to look at logs and whatnot. But if this isn't supported, I'll drop it with this board. Thank you!

[TDK]

Yes. The grounds will need to be compatible as they will be tied on the board.

Shouldn't need to test if a battery power supply works. But yes you can.