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TLV9151: Feedback Capacitance vs. Load capacitance

Christoph Hillebrand
Prodigy 20 points

Part Number: TLV9151

Tool/software:

Hello, 

we use TLV9151 in our system. 

We evaluate different feedback capacitors C_F. 

With 100nF, we achieved superior performance than with 1nF in our system. 
But we are afraid about the 1nF capacitive load driving specification in the datasheet. 


Do you see any problems in using a 100nF for C_F in this case?

  • 0
    TI__Guru* 77501 points

    Hi Christoph,

    Christoph Hillebrand said:
    Do you see any problems in using a 100nF for C_F in this case?
    Christoph Hillebrand said:
    With 100nF, we achieved superior performance than with 1nF in our system. 

    The C_F capacitor across the RF resistor is used to limit the BW of an op amp. The op amp instability issues are not determined by the C_F feedback capacitor, rather it is determined by how much capacitive load that the Vout node is driving directly. 

    Please specify the RF and RG resistors values in the attached circuit including the capacitive load, we can simulate the output behavior or op amp stability per your application. 

    If you have other questions, please let us know. 

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    Prodigy 20 points

    R_F = 10kOhm
    R_G = 910 Ohm 

    Capacitive Load at the output directly is limited to uC-ADC input and parasitic capacitance. I would assume <100pF, maybe you can check it with 100pF and 10pF in both cases. 

    Thank's for your help. 

  • +1 in reply to Christoph Hillebrand
    TI__Guru* 77501 points

    Hi Christoph,

    Christoph Hillebrand said:
    Capacitive Load at the output directly is limited to uC-ADC input and parasitic capacitance. I would assume <100pF, maybe you can check it with 100pF and 10pF in both cases. 

    Based on the information you provided, you limited the the op amp's BW significantly. Your ADC is not sampling very fast, and you can lower the pole in RC filter at the op amp's  output stage and removed unwanted high frequency noise from the system.  The circuit will be stable as long as you do not see overshoot from the simulated step transient in small signal or in actual non-inverting setup on your bench or test board.    

    TLV9152 fp 07302025.TSC

    If you have other questions, please let us know. 

    Best,

    Raymond