TPS54824: Phase margin and Gain margin measurement

Chun-Ching Huang

Prodigy 10 points

Part Number: TPS54824

Dear Team,

Wish you have a good day!!

Let me know what the Start frequency/Stop frequency of the bode plot measure setting?

On my side, I usually set the Start frequency to 1KHz and the Stop frequency to 1Mhz.

Could the frequency span for the horizontal axis be set to 10Hz for the Start frequency and the Stop frequency to 1MHz?

The below measure waveform is setting a frequency span between 10Hz to 1MHz, just want to know if the phase waveform oscillation before 100Hz is normal?

Thank you.

10 months ago

+1 Tahar Allag 10 months ago

TI__Mastermind 29550 points

Hello Chun,

The Bode plot looks good, it has good phase and gain margin are good. 100Hz start is fine. The only concern i have the loop bandwidth. Please use equation to design COUT for the better bandwidth. you can also use webench to help you design the right compensation.

Once the BW is improved . please run transient to make sure the systems is stable.

Thanks

Tahar

0 Chun-Ching Huang 10 months ago in reply to Tahar Allag

Prodigy 10 points

Hi Tahar,

Could you let me know what the cause affects the phase waveform oscillation before the 100Hz? Do I have to fix it?

If yes, can you provide the solution for me?

Many thanks.

+1 Amod Vaze 10 months ago in reply to Chun-Ching Huang

TI__Mastermind 23140 points

Hi Chun,

See section 4.2 of this app note: https://www.omicron-lab.com/fileadmin/assets/Bode_100/ApplicationNotes/DC_DC_Stability/App_Note_DC_DC_Stability_V3_3.pdf The injection signal amplitude needs to be increased at lower frequencies since the DC gain of the converter is high. This keeps the SNR ratio good enough to have a clean measurement. This is not necessary in order to ascertain stability since as the gain reduces, the measurement gets cleaner like in your case. The design looks stable to me. But as Tahar mentioned, you can optimize the compensation to increase the bandwidth possibly depending on what switching frequency you are running the design at.

Thanks,
Amod

0 Chun-Ching Huang 10 months ago in reply to Amod Vaze

Prodigy 10 points

Hi Amod,

Understood, thank you for your reply.

Thanks.

Chun.

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TPS54824: Phase margin and Gain margin measurement