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TPS62097: Datasheet layout example

K. Sasaki14
Guru 10200 points
Part Number: TPS62097

There is a TPS62097 layout example on the datasheet Fig 32.

In this Figure, AGND pin is connected to input capacitor. 

I think that input capacitor GND has large noise and it is not optimal for AGND connection point. So I think it is better that AGND pin is connected to MODE resistor, SS capacitor, FB resistor and PGND pin under the device without connection to input capacitor.

What do you think about my idea?

Best Regards,
Kohei Sasaki

  • 0
    TI__Expert 8420 points
    Hi Sasaki-san,

    we recommend NOT to connect AGND and PGND under the device for this IC. This would add noise into the AGND pin which is sensitive
    Please follow the layout

    Thanks
    Sabrina
  • 0 in reply to Sabrina
    Guru 10200 points

    Sabrina-san,

    Thank you for your answer.
    I would like to know the reason why AGND pin noise increases by connecting AGND and PGND under the device for this device. Are there any special factor?
    Is it noise level larger than input capacitor GND?

    I think other almost device AGND pin is connected to PGND and thermal PAD under the device.

    Best Regards,
    Kohei Sasaki

  • 0 in reply to K. Sasaki14
    TI__Expert 8420 points
    Sasaki-san,

    This device has been designed this way. PGND pin is pretty noisy, it could affects the AGND pin when connected right under the device. So we recommend to connect them further away at the input cap.

    Thanks
    Sabrina
  • 0 in reply to Sabrina
    Guru 10200 points

    Sabrina-san,

    Thank you for your answer.
    I understood TPS62097 PGND pin is pretty noisy. 
    However I think input capacitor GND noise is larger than output capacitor GND. So generally, I think output capacitor GND is better position to connect AGND than input capacitor GND.

    But do you recommend input capacitor point because output capacitor GND is near the PGND pin, right?

    Best Regards,
    Kohei Sasaki

  • 0 in reply to K. Sasaki14
    TI__Expert 8420 points
    Sasaki- san,

    Yes you are right

    Best regards
    Sabrina