TPS40200: Switching frequency variation?

Julio Apps

Part Number: TPS40200

Team,

We are using the TPS40200DRBT in a current design (36V to 12V buck converter application), and I have a question about switching frequency variability.

I have R_rc set as 60.4k and C_rc set as 330pF. The output is stable at 12V, but the switching frequency is ~ 406kHz (I was expecting a switching frequency closer to 477kHz). How much variability can I expect when setting the switching frequency with this part

over 5 years ago

0 Frank De Stasi over 5 years ago

TI__Guru 73575 points

Hello

Based on the data sheet it looks like the tolerance could be as high as +/- 15%.

However, I would double check your RC components values and tolerance.

And also be sure that switching is stable and the device is not in a protection mode

such as current limit.

Thanks

0 Julio Apps over 5 years ago in reply to Frank De Stasi

TI__Expert 3665 points

HI Frank,

I asked the engineer to join the conversation as well but per the datasheet snippet below, it looks like the oscillator frequency can vary by about +/- 15% (I am measuring about 15% low). Can you clarify the “Frequency line regulation” specification below?

0 Frank De Stasi over 5 years ago in reply to Julio Apps

TI__Guru 73575 points

Hello

Yes; that would be another source of variation.

As the input voltage is changed the frequency will also change.

Thanks

0 Julio Apps over 5 years ago in reply to Frank De Stasi

TI__Expert 3665 points

Hi Frank,

To make sure i understood correctly. There is a +/-15% variance in switching frequency just due to oscillator and than the additive variance due to VDD voltage. So the set frequency can vary up to 35% of the set value?

0 Frank De Stasi over 5 years ago in reply to Julio Apps

TI__Guru 73575 points

Hello

I think the way to read it would be that there is a -20% variation when going from 4.5V to 12V that would add to the osc

variation. And a -9% when going from 12V to 52V.

Thanks

0 Frank De Stasi over 5 years ago in reply to Frank De Stasi

TI__Guru 73575 points

Hello

I hope your question has been answered.

I will close this post due to inactivity.

Thanks

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TPS40200: Switching frequency variation?