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Original question:

LMH6720: LMH6720

LMH6720: LMH6720 oscillation

DRUILHE yvan
Intellectual 640 points

Part Number: LMH6720
Other Parts Discussed in Thread: OPA691

Hello

An LMH6720 operational amplifier has taken the place of a CLC410 on an existing board. Ground planes located beneath the operational amplifier on the board are undoubtedly producing parasitic capacitive coupling, which could feed an undesired signal back to the non-inverting input and result in oscillations at 35 MHz. Do you believe that an operational amplifier of the OPA691 type, which has a lesser bandwidth of 280 MHz, would perform better in these circumstances?

We would rather not reroute the board.

Thank you for your help.

  • 0
    TI__Prodigy 520 points

    Hi Yvan,

    The OPA691's lower bandwidth should help mitigate some of the parasitic effects, but only to an extent. With all of our high speed parts, including the OPA691 and LMH6720, we recommend cutting out the ground planes below the chips to eliminate the parasitic capacitances. I would recommend trying the board out with the OPA691 and checking for any oscillations. If there are oscillations, we could try and tune the feedback resistances to combat this. However, the recommended approach would be the cut out the ground planes as mentioned before. 

    Best,

    Lukas