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TLV27L1: Unstable performance

Part Number: TLV27L1

Dear Sir/Madam,

I am using TLV27L1IDBVR. The circuit is unstable, after I removed C7, and it becomes stable. Can you explain why?

I am using compliance voltage at input. I have a constant current source 23mA as supply. The compliance voltage is 4.5V higher when it is unstable. Good compliance voltage is 8.85V.

Hope to hear from you soon!

Thanks and best regards,


  • Hi KH,

    C7 is connected to the inverting input pin. Having additional capacitiance on the inverting input creates delay in the feedback of the op amp causing instability.

    Another way to think about is to use poles and zeros. The capacitance adds a zero to the 1/Beta curve causing a Rate of Closure (ROC) of 40dB/dec. Which leads to instability. I recommend watching our TI Precision Lab videos on Stability for more information. The videos will teach you how to similate the Aol and 1/Beta curves so you can measure the phase margin and ROC.

    Does C7 have to be in the design? If not, I recommend removing it from the design. If it is required for the design you will need to stabilize the amplifier. This is typically done by placing a capacitor in parallel with R13.

    Thank you,

    Tim Claycomb

  • KH,

    C7 creates a pole which reduces the phase margin of the op amp feedback loop. Frequency compensation must be added to improve phase margin of the loop when the C7 is installed. What is the oscillation frequency and waveform shape when it is unstable?