Original question:
Team,
My customer finds one OPA2171 output vibrate issue, due to phase margin(Rout=30Ohm, C=1000pF):
We look into other competitor's D/S, when R=50Ohm, C_Load higher than 1000pF, the phase margin is optimized. Take this pic as example:
Please help to give:
1. OPA2171's similar test result as above.
2. Any other suggestions to optimize the output vibrate issue.
Thanks!
Hello,
Thank you very much for your support!
Please see the SCH as below and help to give some suggestions. By the way, we don't have the phase vs cap load image, right? I'm asking because we want to see if it's possible to increase the 1000pF cap value to optimize the phase margin.
Hello Qiang,
The stability of the op amp is dependent on the output impedance of the op amp. Therefore to drive a capacitive load, different op amps will require different stability compensations. There is a TIPL Stability curriculum linked here.
For the OPA2171, there will be a significant decrease in % overshoot if the the 30 ohm is increased to a 50 ohm, as seen in Figure 38 & 39 of the datasheet:
1. OPA2171's similar test result as above.
For your original question, the answer is found in Figure 45.
I recommend the customer also try the OPA2991. The performance driving 1000pF capacitive load is better than the OPA2171:
All the best,
Carolina
