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OPA2209 output Ripple

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Replies: 1

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Hi,

I simulated the following amplifier circuit using OPA2209. Input is 2.5VDC. Output has ripple voltage instead of 5VDC output.

Can you please tell me what could be the cause for this behavior? I attach the Ltspice simulation files for reference.

5V_Output_Gain=2.zip

1 Reply

  • Shihab,

    Using large 50k gain resistor, R2 and R3, cause a zero in the close-loop transfer function around f=1/(2πRCin)=1/(6.28*50k*6pF)=~530kHz, resulting in an instability of the circuit. In order to stabilize the circuit, lower the values of the resistors by 10x or try to compensate it by placing ~6 pF cap across feedback resistor.

    Also, OPA2209 includes input bias current cancellation circuitry thus IB polarity may be positive or negative - for that reason, please remove R5 series resistor from non-inverting input since it will not cancel the effects of the input bias current.

    Marek Lis, MGTS
    Sr Application Engineer
    Precision Analog - TI Tucson

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