split pic psu

santa_pic · Guest

Hi folks,
just want to check an idea out for powering a pic, instead of using a normal 0-5v dc supply, would it be possible to use a psu of +2.5 to 0v to -2.5v dc with pic connected across +2.5 and -2.5, has anyone done this?
My thoughts for doing this are for using low voltage op-amps 0-5v but allowing them to swing around the zero to either +/- 2.5. Obviously the pic on its A/D would see 0v as +2.5 with respect to its VSS supply pins attached to the -2.5 line. Any thoughts on this?
Dave

Guest · Posted: Thu Dec 06, 2007 9:45 am

The PIC can't tell how it is hooked up.

The Digital IO lines would be -2.5 to +2.5 volts also - which would make interfacing to any other logic interesting.

In circuit programming would be out using a standard ICD unless you built a I/O level shifter to get the levels of the ICD tot he PIC.

Sounds like a lot of extra issues - You can level shift the A/D input using resistors - right? Perhaps this is an easier solution...

HTH - Steve H.

Ttelmah · Guest

There is nothing wrong with this at all. It is just down to nomenclature. You are simply calling the PIC supplies -2.5, and +2.5, working relative to an analog 'ground' between these rails. If the currents are low, and you have not already designed the supplies, you might want to look at some of the 0v generator chips around. Both Maxim, and TI, do chips that generate a 'mid rail' ground for this type of application, so you run with 0v, and 5v, and these develop a centre rail, designed as the 'ground' for op-amps in exactly this type of application. Have done it on many occassions.

Best Wishes

bwhiten · Joined: 26 Nov 2003 Posts: 151 Location: Grayson, GA

Ttelmah,
I searched the web for these 0 volt generators but the name didn't hit. Can you give me a part number so that I can tell what they are called in the industry?
Thanks.

Ttelmah · Guest

Vmid generator IC's, or 'virtual ground' IC's. Look at the TLE2426, which is the Texas one I ended up using.

Best Wishes