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LMZ31710: the possible risk if AGND and PGND are not separated

Noriyuki Takahashi
Genius 10980 points
Part Number: LMZ31710

Hi team,

I understand the device recommend that  AGND and PGND need to be separated in order to protect AGND from noisy PGND. 

But I am still not sure what can happen if AGND and PGND are not separated. Could you tell any possible risks?

Regards,

Noriyuki Takahashi

  • 0
    TI__Mastermind 35165 points

    Hi Noriyuki-san,

    In general noise on AGND can affect the internal analog control circuits that use external components with AGND as their reference. Based on my experience with this family of devices, the primary noise sensitive pins would be the VADJ, ISHARE and RT/CLK. Noise on VADJ pin could cause jitter or affect load regulation. ISHARE is connected to the output of the error amplifier so noise on the ISHARE pin could cause jitter. Noise on RT/CLK could cause switching period jitter. With very bad layout with a lot of noise on AGND it could result in very erratic switching.

    Anthony

  • 0 in reply to Anthony F
    TI__Genius 10980 points

    Anthony,

    Could you tell more the details of the meaning of the erratic switching?

    I can't understand the state of the erratic switching.

    Regards,

    Noriyuki Takahashi

  • 0 in reply to Noriyuki Takahashi
    TI__Mastermind 35165 points

    By erratic switching I mean an extreme amount of jitter in the SW node pulse-width and on-time.