AD629 - Instability & Oscillations

Hello Dear Community,

We are using AD629 (will be replaced with AD8479 in our next revision for its rail-to-rail output) to measure high voltage (5000V - DC & PWM -). Bellow is the schematics of our implementation:

During the first test, we wanted to validate the AD629 implementation. So, we injected a small signal (0-2.5V) that has 1us rise/fall time, and 30us on/off time.

As result, we have seen oscillations on the output (around 250KHz) as you can see in the below scope traces. We got the same results even when disconnecting the following stages (AD8138...).

Same results is observed when using small signals at the input (50mV):

We decided to build the same circuits on a test board. The results was the same.

What do you thing about this problem? Is it because AD629 has kind of high slew rate or maybe because of its slow settling time... maybe both or some other factors can cause such an issue?

Please, help it is kind of urgent.

Thank you



Changing the schematics
[edited by: abderrezak at 2:27 PM (GMT -4) on 20 Oct 2020]