TPS54227: TPS54227 - about inductance(L)

I don't normally support TPS54227 any longer. I can make some comments. First off, you need to be careful about minimum off time.

For min off time = 310 nsec, the minimum Vin for 3.3 V output = 4.12 V

The inductor value is chosen to keep the LC resonant frequency close to the internal ripple injection zero frequency. Increasing Lout lowers the resonant frequency and may cause the phase margin to be lower.

Transient response will mostly be affected by the fact that duty cycle is near the maximum. to respond quickly, the duty cycle needs to increase. if it is near or at the maximum, it cannot increase further.

You probably cannot maintain regulation at 4 V input. The regulation will be degraded slightly until Vin is about 5 V.

let me know if you have further questions.

Hi Hirotaka Matsumoto-san,

Agree with John's advice.

1, input voltage better no smaller than 4.5V as datasheet showed.

2, if L value too large, LC dobouble pole will goes to lower frequency, this maybe cause lower phase margin. then cause the converter not stable, such as transiet fail.., you'd better follow the recommendation table value in datahsheet, include L, Cout and even Cff value.

BR,

Yuchang