TPS54528 increase output volateg in load regulation

KIYOSHI NARISAWA1

Expert 1510 points

Other Parts Discussed in Thread: TPS54528

Dear TI

Customer has a question about load regulation.

Output valtage of TPS54528 is inceased at translatoin from DCM to CCM and it's depends on sample.

One is 30mV and the other is 6mV between 1mA and peak.

Customer would like to know the reason why is different between sample and sampleand what is the root cause?

On time is different and therefore ripple is also is diffrent, but I don't know why it effect peak voltage in load regulation.

Could you please that mechanism?

Please take a look an attaching file.

Best Regards

K.Narisawa

TPS54528_Load regulation.pdf

over 10 years ago

0 JohnTucker over 10 years ago

TI__Guru**** 191445 points

During DCM, the TPS54528 is operating in eco-mode. In eco-mode operation , the ripple is increased above the comparator threshold. so the average output voltage should increase as the output current decreases as shown in the datasheet load regulation curves of figure 4. I am not sure why yours would decrease below the threshold. I have never seen that type of regulation curve before with any of these or other closely related devices. Is it possible the voltage is not measured correctly?

As far as the offset difference, it is only 0.3%. I think that is reasonable part to part variation.

0 KIYOSHI NARISAWA1 over 10 years ago in reply to JohnTucker

Expert 1510 points

Hi John-san,

Thank you for your reply.

Yes, as you mention, when output voltage is 1.05V, it's same as figure 4. But in case of 5V, it's different.

An attaching file is same sample.

This phenomenon is not issue in customer side in this time, but she want to know the root cause what is effect for increase value between sample and sample

from 100mA to 300mA output current.

Thank you for your help.

Best regards

K.Narisawa

TPS54528_Load_Regulatoin Comparison.pdf

0 JohnTucker over 10 years ago in reply to KIYOSHI NARISAWA1

TI__Guru**** 191445 points

I'll see if I can correlate that. it will most likely be next week before i can find an answer.

0 JohnTucker over 10 years ago in reply to JohnTucker

TI__Guru**** 191445 points

I verified that the output voltage does start to rise then fall back as the load is decreased. I am not sure why, but it probably has to do with the adaptive on time controller. I will consult with an IC designer next week.

0 KIYOSHI NARISAWA1 over 10 years ago in reply to JohnTucker

Expert 1510 points

Hi John-san Is there any update after consulting with designer?
If you have, please let me know.My mail address is narisawa-k@clv.macnica.co.jp
K.Narisawa

0 JohnTucker over 10 years ago in reply to KIYOSHI NARISAWA1

TI__Guru**** 191445 points

We do not fully understand the difference. It is just the way it works. Do you have a compelling need to know?

0 KIYOSHI NARISAWA1 over 10 years ago in reply to JohnTucker

Expert 1510 points

Hi John-san,

I'm sorry to late my response.

After investigating output voltage increasing,it was caused by 22pF of cff.

Customer added 22pF of cff with 22uF x 2pcs Cout. And she wants to know a reason why incease output voltage between 100mA to 300mA only.

She will add more capacitor on Cout due for phase margin, therefore added 22pFof cff.

Could you show me that mechanism?

narisawa-k@clv.macnica.co.jp

Thank you for your cooperation

K.Narisawa

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TPS54528 increase output volateg in load regulation