STLINK-V2 VAPP Pin - Is this an input or output? If the STLINK is 3V3, how do I connect to a 2.5V target without damaging it?

[John123]

Hi all, I have designed a target board that operates at 2.5 to 3V. Is the STLINK-V2 SWDIO and SWCLK 3V3?

Will it damage my board?

Is the STLINK VAPP pin an input or an output i.e. does it sense my target supply voltage and level-shift accordingly?

If so, will it be fairly high impedance i.e. not draw too much current from my target?

The wording in the STLINK doc is unclear:

 

[Andrew Neil]

Yes, it is an input - it is how the ST-Link knows what voltage levels to use with your target.

As the note you highlighted says!

 

PS:

Is the STLINK-V2 SWDIO and SWCLK 3V3?

This is clearly stated in the User Manual:

 

 

[John123]

Many thanks.

I still can’t understand the footnote (a) in the attached extract.  This implies STLINK-V2 always outputs 3V3 , and could damage the 2.5V target board.

If you could clarify this footnote then very much appreciated, John.

[Andrew Neil]

This implies STLINK-V2 always outputs 3V3 , and could damage the 2.5V target board.

It specifically states that it will not damage an STM32 target:

 

[TDK]

VAPP is an input to the programmer. The programmer does not drive it. No issues there.

The ST-LINK/V2 (you should be precise in naming this to avoid ambiguity) outputs 3.3V signal on SWDIO/SWCLK. This will not harm an STM32 chip operating at 2.5 V and is within datasheet operation conditions. If the only thing those signals are connected to are the STM32 (which is typical), there is no issue here. Other programmers can be used if you do not like this, as outlined in the footnote.