UC3825: The phase of output A & B

Chun Hung Chen

Intellectual 590 points

Part Number: UC3825
Other Parts Discussed in Thread: UC3823

Hi TI team

I'd like to know output A & B of UC3825.

Are they reverse each other, or phase difference angle??

Thanks

over 4 years ago

0 Colin Gillmor over 4 years ago

TI__Mastermind 25570 points

Hello Chen

The two outputs are the same but there is a 180 degree phase shift between them. The design example on P8 of the data sheet shows the controller being used to control a push-pull power stage.

Regards

Colin

0 Chun Hung Chen over 4 years ago in reply to Colin Gillmor

Intellectual 590 points

Hi Colin

Thank you for your answer.

The duty cycle of each output is 49% (< 50%).

I don't know could this IC work on CCM.

Andy

0 Chun Hung Chen over 4 years ago in reply to Chun Hung Chen

Intellectual 590 points

Hi Colin

I'd like to know how much the exactly maximum it could be.

Could I use output A & B to drive the same one Mosfet to achieve 99% duty?

Thanks

0 Peter Meaney over 4 years ago in reply to Chun Hung Chen

TI__Mastermind 31580 points

Hi Chung,

If you combine the A&B gates there will be some deadtime between the gate drive pulses even at maximum duty cycle. A finite amount of time is required to reset the timing ramp internally and this results in a maximum duty cycle of less that 50% or 100% in practice.

Regards

Peter

0 richard payne over 4 years ago in reply to Peter Meaney

Genius 4640 points

Note that 50% duty cycle applied to each channel A or B. Not both A and B.

I used UC3825 for push-pull where duty cycle actually goes to 95% depending on slope compensation adjustment. Datasheet may need to clarify this meaning.

I have not used UC3823 (which quoted100%) so I cannot comment.

0 Chun Hung Chen over 4 years ago in reply to richard payne

Intellectual 590 points

Thank you.

0 Chun Hung Chen over 4 years ago in reply to richard payne

Intellectual 590 points

回复彼得·梅尼

Hi Peter

I used UC3825 for push-pull where duty cycle actually goes to 95%.

Does it mean the duty of A & B is 95%/2?

Thanks

0 Chun Hung Chen over 4 years ago in reply to richard payne

Intellectual 590 points

Hi Peter

goes to 95%

How many of the switching frequency is it?

Thanks

0 richard payne over 4 years ago in reply to Chun Hung Chen

Genius 4640 points

Yes that correct.

0 Chun Hung Chen over 4 years ago in reply to richard payne

Intellectual 590 points

Hi Payne

Yes, that correct.

Reply to the duty of A & B is 95%/2?

When duty goes to 95%.

How many of the switching frequency is it?

Thanks

0 Peter Meaney over 4 years ago in reply to Chun Hung Chen

TI__Mastermind 31580 points

Hi Chung,

Page 6 of the datasheet shows the deadtime and how the deadtime varies with the value for the Ct, timing capacitor. The deadtime is the time take to discharge the timing capacitor at the oscillator period. The deadtime reduces the maximum duty cycle available.

The A and B outputs operate at 50% duty cycle in theory, this will be reduced by the deadtime which depends on the Ct value. What value of Ct and Rt do you expect to use?

Regards

Peter

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UC3825: The phase of output A & B