Problem with TC7109 ADC

Hi all,

My application deals with measuring battery voltages using Microchip TC7109CPL(12-bit ADC) and transmitting the data to a pic16f877. To maintain good resolution, I have decided to measure only postive voltages.
The supply to the ADC and PIC controller comes from the lower end batteries of the battery string, and the ADC measures the voltages of all the batteries (the battery channel selection is done using a network of multiplexers) including the ones that power the ADC.
My problem is that I would like to run my system without the need of any negative supplies. The TC7109 has a V- (pin 28) which seems to compulsorily need a negative supply. I tried grounding this pin but it only causes an all high output at the output pins and the POL pin also goes high. Isn't it possible to operate the TC7109 without a negative supply at source?

Regards,
Leo

leojose said:

Hi all,

My application deals with measuring battery voltages using Microchip TC7109CPL(12-bit ADC) and transmitting the data to a pic16f877. To maintain good resolution, I have decided to measure only postive voltages.

Click to expand...

I've never used the TC7109CPL, but why not just use the perfectly good 10 bit A2D in the 16F877?.

I've mentioned the 'problems' with high resolution A2D and D2A before, but 10 bit gives you slightly over 0.1% resolution (at FSD, as meters are always quoted) - so how are you planning to calibrate it to even that degree of accuracy?.

Likewise, what are you planning to use for a voltage reference?, bearing in mind it has to have greater accuracy (and stability) than one part in a thousand. Again, you need attenuators to scale your input voltages, or even opamps to scale them up - these aren't going to approach 0.1% accuracy, never mind the 0.025% resolution from a 12 bit A2D.

Just my thoughts! - why waste time, effort, and money for something which isn't going to have any real benefits.

Hi.
I want to read voltage between 0 to 5 volts.But I dont Konw that given voltage to REF+ and REF- pin and I dont know RINT value.
if you have schamtic please help me.
E-Mail: siamak_pety@yshoo.com

Hi Siamakpourali,

use of interfacing a uP or uC to ton ADC like 7109 is a historic concept when built in ADCs were not prevenet in uP or uCs. Now a days , as rightly pointed out by Nigel, there appears no need for resorting to 7109 in conjunction with PIC uC, unless someone insists on you for practice purpose-- that even is pushing you backwrds with time- perhaps you could convince the othe person that you could well go ahead with PIC ( select a suitable one) and get the saame result. thus you get a design with componenet minimun. Any design, i believe, simple is stable and better.

programming, of course you have to practice and derive satis faction and experience.. all the best

Here's an app for the 7109: **broken link removed**

It needs the -supply to operate properly. There are many other solutions to your dilemma. A PIC18F452 has a nice 10 bit A/D on board.