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TPS65916: Separated GND

Kirill Kirillov
Intellectual 370 points
Part Number: TPS65916

Hello. There is a question about layout for TPS65916. One of common rules for impuse source layout is to use separated GND polygon for source currents which is connected to main GND in one point. In DS Layout guidelines for TPS65916 exsits sentences "Use a solid ground-plane for the power ground (PGND) " and "Use an independent ground for logic, LDOs, and analog (AGND)".

Question 1: Does first sentence means that input and output capacitors need to be connected to MAIN solid GND without separation on local GND polygon? 

  • 0
    TI__Expert 8730 points
    Hi,

    I have assigned your request to responsible Applications Engineer and we will get back to you as soon as possible.

    Regards,

    Murthy
  • 0
    TI__Genius 10000 points
    Kirill,

    Thanks for reaching out on E2E. The datasheet has a mistake in saying "Use an independent ground for logic, LDOs, and analog (AGND)" and will be corrected in the next revision. The SMPSx and LDOx signals should all use the Thermal Pad (PGND).

    The REFGND is used as a low-noise ground signal for internal reference, where as the Thermal Pad will have some switching noise. We don't recommend connecting them directly together, but rather have some distance between the two. However, you can connect everything to the same ground plane.

    Please let me know if this answers your questions.

    Thanks,
    Nastasha
  • 0 in reply to Nastasha
    Intellectual 370 points

    Thaks for answering, Nastasha. There are additional questions appeared. As i understand all GND pins of (input capacitors (SMPSx_IN) AND output capacitors (SMPSx_SW) AND input capacitors (LDOx_IN) AND output capacitors (LDOx_OUT)) i should connect to separate GND polygons (one for SMPSx AND one for LDOx) under PMIC and connect both in one point (on PGND). Am I right?

    And where it should be better to connect REFGND? Simply on main board GND?

  • 0 in reply to Kirill Kirillov
    TI__Genius 10000 points

    Kirill,

    You don't have to use separate GND polygons, but you can if you want. The most important things are listed below:

    1. You should have a large GND plane (likely a whole layer of the PCB) that all your components use. (You can also connect all your GND polygons to this layer if you have them.)

    2. When connecting the capacitors, the polygons, and the thermal pad to this GND plane, use several vias to reduce the resistance.

    3. Keep your input caps as close as possible to the device.

    These three tips will all reduce the noise on the GND signal. For the REFGND, you can route it to the GND of an LDO cap or the VBG cap, which are all low noise.

    Please let me know if this helps.

    Thanks,

    Nastasha

  • 0 in reply to Nastasha
    Intellectual 370 points

    Ok, I understood. Thanks for answering.