UCC38083: OCP for UCC38083 with slope compensation

Billy Huang7

Part Number: UCC38083

I am interesting to use a PWM IC, UCC38083, and employ it to implement a DC/DC full bridge converter.

Unfortunately, the pulse current of MOSFET is very large as the output short- circuit test,

because I must choose a smaller current sense resistor value and R_{_I}set value to implement enough slope compensation (The maximum duty cycle is upon 40~43%) for a stable operation.

But it causes the peak current protection insufficient. I do trade-off very hard between a stable steady-state operation and a safe transient-state operation, but I can't do well.

May I ask some suggestion for satisfing both, or use a smart method to do a insufficient and fast peak current protection with enough slope compensation.

Thanks for your patient reply.

Sincerely,

Billy

over 7 years ago

0 Peter Meaney over 7 years ago

TI__Mastermind 31580 points

Hi Billy,

Have you used the application note to calculate the current sense resistor value?

www.ti.com/.../slua584a.pdf

Regards

Peter

0 Billy Huang7 over 7 years ago in reply to Peter Meaney

Prodigy 60 points

Dear Peter

Yes, I have used the application note to calculate the current sense resistor value, but the PWM is not stable enough.

Even, I must make the compensating slope is near to 100% of the output inductor current down slope as it appears at he current sense input, when the duty cycle is near to 40~43%.

However, the sufficient slope compensation causes the maximum peak current of MOSFET is high when the transient state.

Sincerely,

Billy

0 Peter Meaney over 7 years ago in reply to Billy Huang7

TI__Mastermind 31580 points

Hi Billy,

You should not need 100% slope compensation, I would have thought once you are above 50% or the down slope you should be ok.

Can you send me on the calculations including the output L vale, Vout, etc?

What happens if you run the controller open loop and hold the CTRL pin at a DC voltage at 40% to 43% duty cycle, does the design still oscillate?

Regards

Peter

0 Peter Meaney over 7 years ago in reply to Peter Meaney

TI__Mastermind 31580 points

Hi Billy,

Since there has been no activity on this post for two weeks I am closing the post.

Please open a new post if you have more questions.

Regards

Peter

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UCC38083: OCP for UCC38083 with slope compensation