LM5032 (Duty cycle max)

Diane ASSOUMOU

Other Parts Discussed in Thread: LM5032, LM5119, LM5117, LM5023

Hi,

I would like to use the LM5032 for Buck converter because it's perfect to my apllication, the only problem is the duty cycle max 80%.

I need to know how can i do to use it with a duty cycle > 80 %.

is it possible to use the SYNC fonction to avoid this problem ?

Thanks

over 12 years ago

0 Terry Allinder over 12 years ago

TI__Expert 3545 points

Diane,

The LM5023 has an internal ramp that set the maximum duty cycle to 80%. It was design so that the maximum duty cycle could be lowered, but not increased. You may want to look at the LM5117 which has a much higher maximum duty cycle. Or if your looking for a controller that can be interleaved take a look at the LM5119.

Terry

0 Diane ASSOUMOU over 12 years ago in reply to Terry Allinder

Prodigy 50 points

Dear Terry,

We already started the layout with the LM5032 and just noticed this max duty cycle issue lately... So it would be much more convenient if we can accomodate it !

We are synchronising the LM5032 with a Piccolo DSP, by sending a clock signal to the RT/SYNC pin.

So, if we set a natural frequency with RT resistor at 125kHz for example (8µs period), the max duty will be 6.4µs (80% of 8µs). Then if we send a sync pulse after 5µs, we should get a frequency of 200kHz with no duty cycle limitation. Are we right ?

0 Diane ASSOUMOU over 12 years ago in reply to Diane ASSOUMOU

Prodigy 50 points

Dear Terry,

Alternatively, do you have a detailed block diagram of the "oscillator and ramp generator" block ?

I think it would help to understand the limits, and if it behaves as we understand.

Best regards,

Diane

0 Terry Allinder over 12 years ago in reply to Diane ASSOUMOU

TI__Expert 3545 points

Diane,

What is your company email address, I would prefer not to post it to an open forum.

Terry

0 Diane ASSOUMOU over 12 years ago in reply to Terry Allinder

Prodigy 50 points

diane.assoumou@brightloop.fr

or / and

rachid.souahlia@brightloop.fr

0 Diane ASSOUMOU over 12 years ago in reply to Diane ASSOUMOU

Prodigy 50 points

Dear Terry,

Thank you for the document that you sent me, I think is possible to do it.

I have an another question about the SYNC frequency :
For 200 kHz out frequency , Do I have to generate a SYNC frequency at 200 kHz or 400 kHz?

Diane

0 Bob Bell over 12 years ago in reply to Diane ASSOUMOU

TI__Prodigy 220 points

You would need to generate a 400KHz SYNC frequency, if you desire each of the two channels to modulate at 200Khz.

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LM5032 (Duty cycle max)