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Regarding +5V Pin on STLINK-V3MODS


This question pertains to the (relatively) new STLINK-V3MODS programming/debugging device.

The UM2502 Users Manual for this product goes into great detail about using Pin #22 of the castellated edge connector aka +5V for ancillary purposes:

"Pin 22 of the right edge pin connector can drive a 5 V target with a maximum output current

of 200 mA. The 5 V pin is guaranteed to be in the +/- 5% range if the driven current does not

exceed 200 mA."

I attached an ohmmeter between pin #22 and the board's +VBUS pin on its USB connector. Because +5V power from pin #22 would be derived from +VBUS pin I expected to see near zero ohms between these nodes. However, I did not and I'm curious why not.

Is there a microcontroller-enabled pass transistor between +VBUS and pin #22? When is this transistor enabled?


ST Employee


>> Is there a microcontroller-enabled pass transistor between +VBUS and pin #22?

Yes, there is a power switch between the 5V coming from the USB port and the pin #22.

>> When is this transistor enabled?

I don't have the exact details, but the ST-Link V3 firmware decides when to enable it.

Most of the time, it should be ON.

The LD3 green LED will be OFF if the power switch is not enabled.


Can you expand on the operation of the switch to control the 5V output on pin 22? I can not get LD3 to light. There needs to be much, much better documentation for this part.

Pavel A.
Evangelist III

@dantronics Do you plug the st-link into a computer or into a [dumb] charger?