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.

[MR87]

How to enable the 5V output on ST-LINK-V3MODS? There is no evidence on datasheet.

Our V3MODS don't have 5V on pin 22, but LD3 is ON. Can you please explain better how to enable it? Thank you.

[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?

 

[S C]

Hello,

The ST-Link firmware is expected to automatically activate the 5V output when conditions are met for that; typically, in case no signal is present on pin22 at ST-Link startup, when the USB enumeration is completed by the host. This is because the ST-Link (as any USB device) is not expected to consume too much current on the USB in the early phase of enumeration. In case a signal is present (high level) on pin22 at ST-Link startup, the firmware assumes the target is externally powered so it does not activate the power switch at its level. Note that this behavior applies since version V3J6M2; in case of older version please upgrade your V3MODS with STSW-LINK007 - ST-LINK, ST-LINK/V2, ST-LINK/V2-1, STLINK-V3 boards firmware upgrade - STMicroelectronics.

Note that afterwards, in case of target powered by the ST-Link, the ST-Link disables the target power during firmware upgrade.

Currently I don't understand how it could be possible to have no power on pin22 but LD3 ON. Do you have the possibility to check the pin22 signal level ?

[Mike_ST]

UM2502 modifed: "5.2 Power Scheme" is added to better explain the behavior.