TPS61252: Can the CFF in a typical application be changed from 100pF to 1nF?

Gust Zhang

Expert 5791 points

Part Number: TPS61252
Other Parts Discussed in Thread: TPS61253A

Can the CFF in a typical application be changed from 100pF to 1nF? If can, please give an explanation.

over 3 years ago

0 Zack Liu over 3 years ago

TI__Mastermind 34201 points

Hi Gust,

It depends on the upper feedback resistance. Datasheet shows a typical value 768k for Rupper and 100pF for Cff. The feedforward zero frequency is set at Zcff=1/(2*PI*Rupper*Cff). If you change the Cff to 1nF, the Rupper is better to be 76.8kohm.

0 Gust Zhang over 3 years ago in reply to Zack Liu

TI__Expert 5791 points

Hi Zack,

If I do not change the value of the upper feedback resistor, but only change the value of the feedforward capacitor, is it feasible in the application?

0 Zack Liu over 3 years ago in reply to Gust Zhang

TI__Mastermind 34201 points

Hi Gust,

Setting the feedforward capacitor too big will cause the Cff zero is reduced to a much lower value. The cross over frequency would be increase to a higher value and phase margin may be not enough. You can try it on EVM.

0 Gust Zhang over 3 years ago in reply to Zack Liu

TI__Expert 5791 points

Hi Zack,

Can the PWM mode be maintained at all times, and do not enter the PFM mode even at light loads？ If can, how to set up?

0 Zack Liu over 3 years ago in reply to Gust Zhang

TI__Mastermind 34201 points

Hi Gust,

The device will automatically enter into PFM mode at light load.

If you hope the boost converter maintain in PWM mode at full load range, another boost converter like TPS61253A could be selected.

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TPS61252: Can the CFF in a typical application be changed from 100pF to 1nF?