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closed loop output impedance of LM 6172

KARAN GANDHI
Prodigy 20 points
Other Parts Discussed in Thread: LM6172

I am using LM6172 Dual High Speed, Low Power, Low Distortion, Voltage Feedback Amplifiers in voltage follower mode. In the datasheet typical value for closed loop output impedance is given as .01 ohms at 10Khz, Can someone help me in providing the information about worst case output impedance closed loop can I get from LM6172(maximum output impedance) or how can I calculate it.

Thanks

  • 0
    TI__Genius 15975 points

    Hello Karan,

    The closed loop output impedance for LM6172 is close to 0.01ohms. It is usually given by the expression Zout = Ro/(1+(Aol*B)) where Ro is the open loop impedance, Aol is the open loop gain and B is the beta factor.

    As you can see from the LM6172, the open loop gain in the frequency range of 10kHz is very high, which makes the closed loop output impedance close to 0ohms as the open loop gain is in the denominator of the expression for Zout.

    Best Regards,

    Rohit

  • 0 in reply to Rohit Bhat
    Prodigy 20 points

    Hello Rohit,

    Thanks for replying but my question was what can be the worst output impedance that we can expect in audio range because all these are typical values(those provided in datasheet) which can vary from amplifier IC to amplifier IC, so what can be the worst case scenario. 

    Regards,

    Karan

  • 0 in reply to KARAN GANDHI
    TI__Genius 15975 points
    Hello Karan,

    The worst case scenario would be a shift in closed loop output impedance by 10% across process and temperature, which puts the worst closed loop output impedance close to 0.009 to 0.011 ohms.

    Best Regards,
    Rohit