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Electronics => Beginners => Topic started by: amateur_25 on May 06, 2012, 12:12:03 am

Title: Using ADC input pins to route vcc
Post by: amateur_25 on May 06, 2012, 12:12:03 am

Hi
I trying to layout my own pcb based on someone elses schematic. Due to how the board is laid out, it easier to use one of the extra ADC pins avaible on the TQFP package to forward pwr onto the right hand side of the board. The datasheet says it only functions as an ADC input. Am I correct in saying it's safe to do so?

I'm using pin19 on the 328P TQFP.

Title: Re: Using ADC input pins to route vcc
Post by: Psi on May 06, 2012, 12:24:48 am

Do you mean you need to get VCC from one side of an IC to the other and you're asking if you can go "through" an unused input pin?

Title: Re: Using ADC input pins to route vcc
Post by: vk6zgo on May 06, 2012, 04:36:58 am

I don't know the device,but it sounds scary as hell to me! ;D

Title: Re: Using ADC input pins to route vcc
Post by: T4P on May 06, 2012, 05:39:30 am

Does a 328pin TQFP even exist  :o

Title: Re: Using ADC input pins to route vcc
Post by: TerminalJack505 on May 06, 2012, 06:00:03 am

I'm guessing that he is saying that he is going to route to the Vcc pin as well as the unused ADC pin.

I don't see why you couldn't do this.  It is an input pin, after all.

Quote from: Dave.S on May 06, 2012, 05:39:30 am

Does a 328pin TQFP even exist  :o

LOL.  I'm pretty sure he's talking about the "Arduino chip."   :D  Aka Atmel ATmega328P.

Title: Re: Using ADC input pins to route vcc
Post by: Psi on May 06, 2012, 07:40:49 am

You just have to route it so any voltage drops in vcc tracks don't result in a higher voltage on the input pin than the actual VCC pin.
Or it will feed backwards into the chip from the IO and may cause problems.

It's not an issue unless you happen to be powering something else from in between the vcc<->inputpin link.