Regarding +5V Pin on STLINK-V3MODS

[jimolson]

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?

[Mike_ST]

Hello,

>> 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.

[dantronics]

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.]

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