UCC2897A: UCC2897A Duty issue

Part Number: UCC2897A

Tool/software:

Hello, I have two questions to ask:

1.The attached figure shows measured waveforms under different load conditions. It appears that during the medium-load condition, the output duty cycle seems limited and unstable. This issue does not occur under light-load or heavy-load conditions. It doesn’t look like it's caused by CS pin or VDD protection. Do you have any other suggestions for inspection points?

2.Currently, under medium-load/heavy-load conditions, the output voltage drops and doesn’t recover to the set voltage. Could this be due to insufficient DC gain in the loop compensation?

thanks,
JJ

7 months ago

0 Hong Huang 7 months ago

TI__Guru 74115 points

Hi,

It looks at medium load the pulse widths are changing - which is likely due to the loop stability not enough phase margin. You need to tune up the phase margin based on the measurement of the bode plots.

0 JJ 7 months ago in reply to Hong Huang

Prodigy 50 points

Hi Hong,

Thank you for your response. Currently, the ACF(forward) input voltage range is quite wide, from 25V to 120V, with the duty cycle range from 70% to 10%. I tried using the steps in SLUA535 to adjust the compensation network, but I still couldn’t achieve the appropriate phase margin (PM) and gain margin (GM). Do you have any recommended steps for tuning in such a wide input voltage range?