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OPA2836: OPA2386 PCB Layout

Jack Li-SH
Expert 3975 points
Part Number: OPA2836
Other Parts Discussed in Thread: OPA855

Dear sir,

would you please explain why we need remove all  Ground and Power planes under IC,  on page 43 of OPA2836, as following,

Usually most high speed amplifier just need remove the Ground and Power  plane under Vin- pin and resistor . as following,

Thanks to your support!

Regards,

Jack

  • 0
    Guru 140200 points

    Hi Jack,

    maybe the layout was adapted from a similar layout which had removed the solid ground completely under the chip in order to prevent a short circuit to a thermal pad?

    Unfortunately, the recommended layout of OPA855 you have shown is no good example how the ground plane should be removed. You may want to read this thread:

    https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1089964/opa855-q1-output-layout-instruction

    Kai

  • 0
    TI__Mastermind 20206 points

    Hello Jack,

    Kai's linked discussion is worth a read; I can consult with my team members on our recommendations and explanations for the differences and best practice for high speed PCB layout.  Please allow me a bit of time to have that discussion; my goal is to make both a recommendation for the OPA2836 and also a general recommendation for your future designs.  

    Kai,

    Thank you for recollecting the thread with your documented PCB recommendations.

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    TI__Mastermind 20206 points

    Hello Jack,

    The reasoning for the OPA2836 PCB layout shown in the datasheet is simple: ease of design.  The OPA2836 does not have a thermal pad; it was likely easier for the designer to remove an entire square under the OPA2836 than for the recommended design approach of cutting out the planes under input traces and feedback paths. 

    As Kai's post and other documentation shows, there is usually a minimum amount of cutout required to satisfy high-speed parts, with some room for simplicity or margin in using larger/simpler cutouts on parts without thermal pads (or similar).  

    Best,

    Alec