Hello Shreehari,
I checked the pinout, and everything looks correct. A few comments:
1. The 22kohm pull-up for the power down pins is a bit high. Worst case, the input current for each of the pins can be +/-10uA. Recommend reducing the 22kohm by a factor of 10, or use 2.2kohm pull-up to guarantee a proper high level voltage.
2. You are using two separate grounds; analog and digital. It is extremely important that a low impedance connection between the analog and digital ground pins of the ADS1278 is provided. I recommend joining the two ground planes directly beneath the ADS1278, through the thermal pad. If this is not possible at the board level, then all ground pins need to be connected to the analog ground plane. Please refer to this E2E thread for additional details.
3. The reference buffer should work well. I suggest you verify that the phase margin of the reference buffer circuit is 60deg or more to ensure best response.
Regards,
Keith Nicholas
Precision ADC Applications
Hello Shreehari,
Stability is a very involved subject. We have several TI Precision Labs on this subject; the lab that specifically talks about the buffer topology that you have used is covered in Section 10.6, TI Precision Labs - Op Amps: Stability - Isolation resistor.
In order to check stability, you can simulate using SPICE.
I simulated using the OPA320, and below is the resulting values that I used to get close to 90deg phase margin. Since you are using a different amplifier, you may need to adjust the values accordingly.
Regards,
Keith
