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LM3524D: LM3524D : Error Amplifier Validation

Sangeethaa Michael
Prodigy 10 points
Part Number: LM3524D

Tool/software:

Hi,

Facing issue in Validating the Offset Voltage of the Error Amplifier Block of LM3524D PWM. Need support on the Test Conditions and the Test Setup Details required.

We tried with basic Servo loop and observed that the Error Amplifier Output keeps switching while trying to maintain the Common Mode Voltage to measure the Offset through Auxiliary OpAmp.

Because of this not able to measure the exact Offset Voltage of EA

Could you please let know how to validate the parameters of Error Amplifier block.

Thanks

  • 0
    TI__Guru 73555 points

    Hi,

    To validate an amplifier you need to set up a precise input signal to the amplifier and measure its output.

    You can search how to test an amplifier on web to get many returns.

    The datasheet page 8 also provides a test circuit.

  • 0 in reply to Hong Huang
    Prodigy 10 points

    Hi Hong Huang,

    Thank you for the response.

    We have tried the similar Servo Loop Setup as shown below which is used for Testing general OpAmp's Offset Voltage

    As per this concept, the output of the DUT has to settle to the Auxiliary OpAmp's reference Voltage. But in case of Error Amplifier in PWM, when the reference of Auxiliary OpAmp (Non - Inverting Pin) is set to Common Mode Voltage of 2.5V, the Output of the DUT keeps oscillating instead of getting settled to 2.5V.

    Because of this the Offset Voltage Measurement is not stable at the Auxiliary OpAmp's Output as it keeps swinging to Saturation

    Kindly let know your ideas

    Thanks

  • 0 in reply to Sangeethaa Michael
    TI__Guru 73555 points

    Hi,

    In switching mode power supply the amplifier is usually used with its gain quite low from external circuit and not used in open loop.

    When you test open loop amplifier, you need to have very precise input voltage control, as usually the amplifier gain is 60 to 80dB, so 1000 to 10000, even 1 mV can cause 1 to 10V which may show stable issue.

    If you want to test amplifier I suggest you to consult amplifier team as we are not good at testing amplifier itself and we usually use amplifier with closed loop.