UCC28C59: Clarification about control loop behavior

Benjamin KOSICKI

Prodigy 30 points

Part Number: UCC28C59
Other Parts Discussed in Thread: UCC2897A

Tool/software:

Hi,

We are using UCC28C59 for a 60W Forward Converter on Simetrix.

Some questions or clarifications about this reference:

- Based on datasheet table 7.1, to obtain 100kHz switching frequency, we need to set Rt = 3.05kR and Ct = 2.2nF. Right ?

- We meet some trouble on output pin, control loop is updated one time on two (see attached screeshoot), first pulse is at his maximal value and the second to the minimal value.

We suspected it may occur due to wrong pole and zero placement. Do you have some application note to set compensator value (we based our compensator value on slva662).

BR,

over 1 year ago

0 Hong Huang over 1 year ago

TI__Guru 73265 points

Hi,

1. Yes, UCC28C59 fsw = fosc /2, to get fsw = 100kHz, fosc needs to be = 200kHz, so Rt = 3.05k-ohm, and Ct = 2.2nF are correct to get this.

2. The CS waveform shows CCM operation, you need add the current slope compensation and tune up to resolve the wider-narrower-wider pulse pattern which is called subharmonic unstable particularly due to the CCM operation without the proper slope compensation.

0 Benjamin KOSICKI over 1 year ago in reply to Hong Huang

Prodigy 30 points

Hi,

Thank you for your reply.

I didn't implement slope compensation due to the sentence "With current mode control, slope compensation is required to stabilize the overall loop with duty cycles exceeding 50%" on datasheet. For me, i won't concerning due to 47% limitation of UCC28C59 version and I was skip the rest of this paragraph.

0 Hong Huang over 1 year ago in reply to Benjamin KOSICKI

TI__Guru 73265 points

Hi,

Your waveform shows CCM operation and shows wide and narrow pulses which usually need to have the slope compensation to resolve.

0 Benjamin KOSICKI over 1 year ago in reply to Hong Huang

Prodigy 30 points

Hi,

Thank you, we solve the problem and we didn't have the problem yet.

Slope-compensation may have a strong impact on current measure, use for Mosfet current protection. Do you have some tips to tune these component (like describe on UCC2897A but for UCC28C59) ?

We found sluaal3 application note, however maybe it exist others documents.

BR,

+1 Hong Huang over 1 year ago in reply to Benjamin KOSICKI

TI__Guru 73265 points

Hi,

You can look at this application note which has a section on slope compensation. It is for UCC28C4x which is pin-to-pin and function to function same as UCC28C5x.

Automotive 40-V to 1-kV Input Flyback Reference Design (Rev. B)

0 Benjamin KOSICKI over 1 year ago in reply to Hong Huang

Prodigy 30 points

Hi,

Thank you for your support.

Have a good day.

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UCC28C59: Clarification about control loop behavior