Two VREF+ pins on STM32G474Q?

[EThom.3]

When I first glanced through the STM32G474 datasheet, I saw VREF+ and VREF- on pins 43 and 44 on the LQFP128 package. "Cool", I thought, although I had no significant need for an actual VREF- pin.

However, when I was making a schematics symbol, I noticed that the two pins are in fact VREF+ and VREF+. Apparently, the exact same thing on two pins next to each other.

Does anyone know why this is? It makes perfect sense to have multiple pins for supply voltage and ground. But for a reference voltage? I have found no explanation in the datasheet or the reference manual.

This question was asked in another thread in December, but no answer was provided. Thread with original question:

https://community.st.com/t5/stm32-mcus-products/vref-stm32g474qe/m-p/750453 

Edit: added screenshot

[EThom.3]

Thanks! :thumbs_up:

I tried to find the schematic, but didn't succeed.

I agree with you that they are most likely internally connected. The reason for it, I won't even try to guess.

[EThom.3]

Criminy!

I scoured the "Documentation" tab, without realising that the schematic was in the "CAD Resources" tab.

[Face palm]

[mƎALLEm · Accepted solution]

Hello all,

Our feedback regarding this subject:

The purpose to have two VREF+ pins is to decrease (to 1/2) the inductance of the bonding wires + lead frame. VREF+ is very sensitive to perfect decoupling (strong voltage) - but when the inductance of wire from pin to the pad on chip is too high then the VREF+ voltage on the die is not perfectly decoupled (there is large inductance). The inductance magnitude is too high on large packages - like LQFP128 (larger wires from pin to pad on chip). Smaller packages inductance is acceptable but for LQFP128 we should decrease this inductance and two VREF+ pins were designed there.

So it's recommended to connect both VREF+ pins externally (even they are internally connected).

I've already suggested (internally) to add a note on the pinout table 2 on both VREF+ pins to connect them externally.

[markproplayers]

Great observation, it seem amazing