UCC28070A: CSS value

Koji Ikeda

Part Number: UCC28070A
Other Parts Discussed in Thread: UCC28070

Hello Support team,

My customer inquires UCC28070 Css value, could you support? Datasheet page 24 note shows "For soft start to be effective and avoid overshoot on VOUT, the SS ramp must be slower
than the voltage-loop control response. Choose CSS ≥ CVZ to ensure this.". Is the risk only for VOUT overshoot? If Css < Cvz, is there any issue except overshoot? They would like to set faster startup, by accepting small overshoot.

Thanks,

Koji Ikeda

over 3 years ago

0 Harish Ramakrishnan5 over 3 years ago

TI__Mastermind 24375 points

Hi Ikeda-San,

Yes, Cvz can be higher than Css to achieve a faster startup. Even the UCC28070 EVM is set up in this way. The purpose of choosing Css > Cvz is to purposely slow the bandwidth of the voltage loop so that it does not see any overshoot.

Thank you

Regards,

Harish

0 Koji Ikeda over 3 years ago in reply to Harish Ramakrishnan5

TI__Expert 6295 points

Harish-san,

Thank you for your support. They would like to confirm if there are any other risk except overshoot, is the overshoot rsk when Css<Cvz?

Thanks,

Koji Ikeda

0 Harish Ramakrishnan5 over 3 years ago in reply to Koji Ikeda

TI__Mastermind 24375 points

Hi Ikeda-San,

Thank you for the reply. There could be overshoot events during AC line dropout for a few cycles which has to be verified as well and it has to be within the allowable system specifications which can otherwise damage components, other than that I do not see risks.

Regards,

Harish

0 Koji Ikeda over 3 years ago in reply to Harish Ramakrishnan5

TI__Expert 6295 points

Harish-san,

Thank you for your support. I'm not sure why Css < Cvz, cause overshoot during AC line drop, do you mean restart event from brown out?

Thanks,

Koji Ikeda

+1 Harish Ramakrishnan5 over 3 years ago in reply to Koji Ikeda

TI__Mastermind 24375 points

Hi Ikeda-San,

Yes restart from brownout that's what I meant.

Thank you

Regards,

Harish

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UCC28070A: CSS value