ads1256: how to compensate capacitance change when change PGA

Jari Saarelainen

Other Parts Discussed in Thread: ADS1256

Hi.

I use ADS1256 in single ended mode and buffer is set to off. I have need to change PGA setting during measurement. I drive input with opamp and I have serie resistor to compensate capacitive load and 1n capacitor to ground on input signal of ADS1256. I have tried value of resistor 47 - 330 ohm. When I connect input of opamp to ground and read ADconversion with PGA 1 - 64, I get results from close to 0 up to 1000000. Is reason for this capacitance change and if so, how to compensate this?

regards

over 12 years ago

0 Christopher Hall over 12 years ago

TI__Mastermind 44720 points

Hi Jari,

Which op amp are you using and how are you powering it? If you're using a signle-supply you may not be able to connect the op amp input to ground.

Also, have you probed the op amp output to check if it is stable?

If you send me a schematic I can attempt to simulate it.

Regards,
Chris

0 Jari Saarelainen over 12 years ago in reply to Christopher Hall

Prodigy 40 points

Hi.

I use LT1882CS with +/-15V supply voltages. I proped meas2 signal and it is stable. Then I have try in-loop compensation, meas1 signal, but this is stil under my tests.

Here is my schematic

2604.ADS1256_demo_verxyz.pdf