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OPA818: PCB design question with OPA818 (cutout plane under V- and Vout)

Simon Francois
Prodigy 70 points
Part Number: OPA818

Tool/software:

Hello TI teams and forum users. 

Firstly hope all is doing well. 

We are finishing our PCB board using multiple OPA818. First as TIA and others as classic opamp. 

We amplify SiPM photodiode which consist of current pulse of 500ns. 

On PCB layout the datasheet recommend to don't have any plane under V- and Vout of all amplifier. 

Do you confirm we have to remove all plane under ? Also the outter one on the oposite side ? And not on the feedback pin ?

On 1 opamp we have a relative long track at the output (16mm) before the next first resistor (the 50 ohm of the next amplifier which contribute to the gain). 

For this should we remove the plane under all the track or for exemple put a 0ohm resistor ? 

Thanks you for your help, 

Have a nice day, 

Simon 

  • 0
    TI__Mastermind 26455 points

    Hello Simon,

      It is recommended to remove the plane right underneath the input and output pins of the amplifier. I can share some resources with you before tomorrow on examples of a TIA layout. For the long track at the output, it would be better to put a 0 ohm resistor near the output pin of the first amplifier, and during testing this might be useful if you need isolation due to parasitics of a long track.

      Are you making sure the tracks are impedance matched at 50 ohms as well? And is your PD close to the input pin of the first amplifier? 

      Would it be possible to share an image of your PCB?

    Thank you,

    Sima

  • 0 in reply to Sima Jalaleddine
    Prodigy 70 points

    Hello Sima,

    firstly thanks you for your reply.

    Of course I can share the board design. It is on Altium, can I zip the project and send it to you ? Would it be possible by mail ? 

    thanks you for your help, 

    Simon