Queries about AD8099

Dear Supporter,

I have a query about AD8099. I use AD8099 in my product. The package is SOIC-8.

The power supply is +/-5V. The gain is set as -10.

Input signal is square wave with the frequency of 2MHz.

After increasing the input amplitude, the output gets its full range.

The output has over-shoot. My schematic and testing results are attached for your reference.

I tested with signal generator and oscilloscope, which means the output doesn’t have capacitive load. We used AD817 and AD847 before, AD817 and AD847 worked well.

I have two queries here.

1, why is there over-shoot here? How can I eliminate it?

2, I read the description of Pin Cc in the datasheet. It is used as compensation for the gain range of –1, +2 to +10. Is it worked for the gain of -10? Is it the over-shoot caused by the poor compensation work design?

Could you please help give some comments on the issues?

Thanks in advance for your help and support!

Br,

Wayne

attachments.zip
  • Wayne,

      -- A scope probe or the input of a scope still has a few pF or more of capacitance.

    --  If the AD817 and AD847 worked, why would you use a part that is 10x faster,

      10x the supply current and much harder to work with?

    --  Over shoot indicates low phase margin.

    --  Are you using a pc board w/ at least four layers?

    --  Do you have two bypass caps on each supply VERY close to the package?

    --  Did you cut away all traces on all layers below the inverting input?

           If you have 1 pF of C on that node, your noise gain will increase with increasing frequency,

      leading to instability.

    --  Did you try making C15 1.1-4.7 pF??

    Harry


  • hello, Harry

    I think I've got your points here and will try with your suggestion. Any update or result will keep you informed.

    Thanks!

    Br,

    Wayne

  • 0
    •  Analog Employees 
    on Aug 2, 2018 2:48 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

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    EZ Admin