ADHV4702-1 Frequently Asked Questions

FormerMember
FormerMember
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  • Hi, I am using ADHV 4702 evaluation board. but the output is too low when frequency going up to 70KHz. below is the list of the output and frequency measurements. the gain network is 40V/V. input is Vpp=4V. I am using the onboard +110/-110 power supply.

    10KHz Vpp=150V
    50KHz 110V
    60KHz 100V
    100KHz 74V
    150KHz 54V
    200KHz 42V
    250KHz 32V

     My design goal is 250KHz, output Vpp=100V. Currently, only work below 60KHz, can  output 100V be reached.

  • Hi Zenlu,

    Thank you for considering the ADHV4702 on your design. 
    Based on your results, I think the amplifier is being limited by the Slew Rate. 
    If you're using the Evaluation board in its default configuration (Aside from the gain network that you changed to 40V/V), the input clamping diodes installed using SBAV199LT1G limits the slew boosting circuit feature of the ADHV4702 as indicated on the User Guide's input clamping section:


    Then looking at the datasheet spec for Slew Rate:

    The external input clamping diodes limits the slew rate to 24V/us, given by the formula:
    Slew Rate = Vo x 2πf; where Vo is the voltage peak, and f is the full power bandwidth;

    With your Vo = 50Vpk and Slew Rate = 24V/us;
    The part can only take an input of around 76kHz. thus going above 70kHz will introduce some attenuation on the output.

    You can try to remove the input clamping diode but I'm afraid this can only accommodate to around 235kHz at your specified Vpeak of 50V or Vpp of 100V.

    I hope this helps Zenlu.
    Let me know if this clears up your concern.

    Best Regards,
    Dann

Comment
  • Hi Zenlu,

    Thank you for considering the ADHV4702 on your design. 
    Based on your results, I think the amplifier is being limited by the Slew Rate. 
    If you're using the Evaluation board in its default configuration (Aside from the gain network that you changed to 40V/V), the input clamping diodes installed using SBAV199LT1G limits the slew boosting circuit feature of the ADHV4702 as indicated on the User Guide's input clamping section:


    Then looking at the datasheet spec for Slew Rate:

    The external input clamping diodes limits the slew rate to 24V/us, given by the formula:
    Slew Rate = Vo x 2πf; where Vo is the voltage peak, and f is the full power bandwidth;

    With your Vo = 50Vpk and Slew Rate = 24V/us;
    The part can only take an input of around 76kHz. thus going above 70kHz will introduce some attenuation on the output.

    You can try to remove the input clamping diode but I'm afraid this can only accommodate to around 235kHz at your specified Vpeak of 50V or Vpp of 100V.

    I hope this helps Zenlu.
    Let me know if this clears up your concern.

    Best Regards,
    Dann

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