OPA2735: Non-inverting amplifier stability

Kavindu Ratnayake

Part Number: OPA2735

Hi,

I'm having some issues with an amplifier circuit which was designed using OPA2735. The output tend to have some oscillations and I'm trying to figure out if it is from the following part of the circuit.

Appreciate if someone can help me to run a stability analysis on this. The Tina- TSC file is also attached herewith.

Stability Analysis OPA2735 .TSC

Thanks in advance,

Kavindu

over 1 year ago

+1 Zach Olson over 1 year ago

TI__Genius 9945 points

Hi Kavindu,

I've performed a stability analysis and determined that the circuit has ~33 degrees of phase margin.

The transient response shows oscillations at the output of the amplifier with an on overshoot of almost 40%

Increasing the first series isolation resistor from 22Ω to 90Ω improves the phase margin to ~50 degrees.

The transient response shows that the oscillations are suppressed with an overshoot of 21%.

If you want to further improve the phase margin and suppress the overshoot, I recommend adding some feedback capacitance in parallel with your 10kΩ feedback resistor. See below phase margin and step response for CF = 50 pF.

OPA2735_Stability_Analysis_ZO.TSC

OPA2735_Transient_Response.TSC

Regards,

Zach

0 Kavindu Ratnayake over 1 year ago in reply to Zach Olson

Intellectual 340 points

Thanks a Lot Zach

+1 Zach Olson over 1 year ago in reply to Kavindu Ratnayake

TI__Genius 9945 points

Hi Kavindu,

No problem, I am happy to help. If you'd like more detail about amplifier stability when driving capacitive loads, I will direct you to this application note that I wrote on the topic: Determine Optimal Isolation Resistance for Driving Capacitive Load

I will go ahead and close this thread for now. Feel free to reply again if you need further support on this design.

Regards,

Zach

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OPA2735: Non-inverting amplifier stability