LMR33630: PGND, AGND split Question.

Seokmin Hong

Part Number: LMR33630

Hello, If I use more than one DCDC Converters and MCUs, then which is right way to split ground?

For example, I am going to use three LMR33630, and each LMR33630 gives power to each MCU.

LMR33630 or any other dcdc converters also have PGND and AGND each.

If I use One DCDC and One MCU, then I will connect DCDC's AGND with MCU's AGND and then connect whole PGND and AGND with 0Ohm.

But If I use more then one, and if each devices's are too far from each other then how to split agnd?

Split each agnd and connect each 0Ohm to pgnd plane?

or connect agnds all together with narrow lines and use only 0 ohm to pgnd plane?

Which is better? Or is this wrong?

Thanks.

over 4 years ago

0 Marshall_Beck over 4 years ago

TI__Mastermind 30660 points

Splitting power planes is not a practice I recommend.

My suggestions is for a 4-layer PCB design, as continuous as possible ground plane in the layer directly underneath the component layer on which the power converter IC is mounted, is recommended, as per the D/S layout considerations section.

0 Seokmin Hong over 4 years ago in reply to Marshall_Beck

Intellectual 485 points

Dear Marshall.

Do you mean then do not split ground?

But there are MCU's that are weak at noise. Can MCU share GND plane with DCDC?

0 Marshall_Beck over 4 years ago in reply to Seokmin Hong

TI__Mastermind 30660 points

Hello Seokmin,

Do you mean then do not split ground? Yes

Continuous ground is paramount for low noise with DCDC. You will often see that recommended in layout guidelines found it datasheet. Please reference layout guidlines in LMR33630 (Section 11.1).

Considering MCU operate above 1.8VDC typically, SNR should be not as much concern in comparison to high performance analog signal chain.

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LMR33630: PGND, AGND split Question.