TPS548B23EVM: Bode plot faliure

Oliver Lin

Part Number: TPS548B23EVM
Other Parts Discussed in Thread: TPS548B23

Tool/software:

Hi team,

My customer is testing our TPS548B23 EVM on bode plot.

We change Lout to 0.82uH and vout setting to 3.3V, frequency change to 600kHz.
At 0% and 50% load, the bode phase margin are under 45 degree. That looks just fail at boundary, I think changing ground and measure again, might see different results. Another thing, if this doesn't work, will you suggest to change any components?

Could please help to check?
Bode test waveform as below for your reference.

Fig1. 0A, Fsw = 600kHz

Fig2. 8A, Fsw = 600kHz

6 months ago

0 Oliver Lin 6 months ago

TI__Expert 4435 points

Hi team,

Some other information from customer,

Since the datasheet specifies that the Bode plot should meet 50°.

BTW, why does this part, which operates in D-CAP mode, require a Bode plot analysis?

0 Tomoya Ide 6 months ago in reply to Oliver Lin

TI__Genius 11146 points

Hi Oliver,

Increasing the inductor from 550nH to 820nH reduces the loop bandwidth, leading to a lower crossover frequency and phase margin. To improve this, we should decrease the output capacitance.

The datasheet recommends checking the phase margin if output capacitance exceeds the maximum limit, as high capacitance can lower the loop crossover frequency and phase margin.

For D-CAP mode, we suggest a target phase margin of 50 degrees to avoid ringing during load changes.

Thank you,
Tomoya

0 Oliver Lin 6 months ago in reply to Tomoya Ide

TI__Expert 4435 points

Hi Tomoya,

We reduced the six 47uF MLCCs to three and added a 220uF POSCAP for testing. The test results are as follows. Is this configuration OK?

Iout:16A,Fsw=600k Hz.

0 Tomoya Ide 6 months ago in reply to Oliver Lin

TI__Genius 11146 points

Hi Oliver,

This configuration looks great!

Thank you,
Tomoya

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TPS548B23EVM: Bode plot faliure