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DRV8311: AGND vs PGND Confusion

Josh Ackley
Prodigy 10 points
Part Number: DRV8311

Tool/software:

Hello,

I am using a battery powered DRV8311P in a motor control application. In my board layout, I am planning to keep PGND and AGND on different ground planes and then connect them near the battery 0V. The datasheet states: "To reduce noise coupling and EMI interference from large transient currents into small-current signal paths, grounding should be partitioned between PGND and AGND." So I believe this design strategy to be sound, however please advise if I should reconsider.

Now, my real question is in regards to the device thermal pad. Table 6-1 in the datasheet states that the thermal pad must be connected to PGND:

However, section 12.1 Layout Guidelines states: "TI recommends connecting all non-power stage circuitry (including the thermal pad) to AGND to reduce parasitic effects and improve power dissipation from the device."

Adding to the confusion as well is that Figure 12-1 Recommended Layout Example in the datasheet does not show any attempt at separating AGND and PGND.

Please provide clarification. Thank you!

  • +1
    TI__Mastermind 26506 points

    Hi Josh, 

    Thanks for bringing this to our attention and I apologize for the confusion! the thermal pad should be connected to a large copper ground pour to dissipate heat away from the driver, and ideally we recommend connecting to AGND since AGND is generally quieter. If there is not as much AGND copper area then it could be acceptable to connect it to PGND if it has a larger copper area for thermal dissipation, however the tradeoff would be potential noise coupling that would need to be considered. AGND is primarily intended for the quieter CSA signals, while PGND is used for paths such as for the motor current. 

    On the recommended layout example, while we do show an example of a common ground implementation there is a tradeoff with the potential for more noise especially on the CSAs. 

    I hope this helps!

    Regards,

    Anthony Lodi