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TINA/Spice/OPA2141: TINA/Spice/OPA2141

Hojin Sung
Prodigy 110 points
Part Number: OPA2141
Other Parts Discussed in Thread: TINA-TI

Tool/software: TINA-TI or Spice Models

Hi, guys

I have a issue from my customer.

1. they made the inverting op-amp, there was output which had osillation.

I don't know why there was osillation..even if I input DC volatge.

But, If I embedded R_load(500ohm) to use shunt, there was no osillation.

2. without R_load, 12mA current flow to -4.8 supply voltage..

it is higher than I_dq(datasheet listed)

I want to solve LDO drop issue.

Please answer ASAP,

Regards,

  • 0
    Guru 140200 points

    Hi Hojin,

    I would remove C219. A high capacitive load at the output of an OPAmp can cause instability and oscillation.

    C213 should also be removed. A capacitance from the -input of OPAmp to GND erodes the phase margin and also causes instability and oscillation.

    Kai

  • 0
    TI__Expert 6250 points

    Hi Hojin,

    This circuit, as drawn, is unstable and may oscillate. An oscillating op amp will draw current in excess of the quiescent current specified in the datasheet. Adding a significant load may affect the op amp's open loop gain or output impedance, creating the illusion of stability, but the best solution here would be to revise the circuit.

    As drawn, the circuit has a -5 degree phase margin:

    and the step response oscillates heavily:

    I'd recommend the circuit below: 

    Here, we remove C213 and place 15pF in parallel with R110. This improves the phase margin to 59 degrees:

    and results in a much more reasonable step response:

    The TINA-TI simulation files for the stability analysis of the original circuit, and the transient analysis of the revised circuit can be downloaded below:

    Stability Analysis of Original Circuit

    Transient Analysis of Revised Circuit