LM3478: About inrush current of LM3478.

watanabe

Part Number: LM3478
Other Parts Discussed in Thread: PMP15044, PMP

Hi,

My customer has a question.

When starting up with the following circuit,
Inrush current flows greatly,
While repeating shutdown and restart by overcurrent limitation,
The output starts up.

Is there a problem with this usage?

If there is a problem,
Is there a way to reduce inrush current?
(Capacitance of the output capacitor can not be changed.)

Best Regards,

watanabe

over 7 years ago

0 Helen chen over 7 years ago

TI__Mastermind 40080 points

The expert for this part is on a business trip and will reply you when he comes back.

The Cout=0.235F is really big, LM3478 can only limit the peak switch current at Vo>Vin condition. At startup when Vin<Vo, the inrush current is uncontrollable and will rise to a very high value. What is the maximum inrush current in your application or what is your maximum Iin? And what is your maximum Vo, Io in this application?

0 watanabe over 7 years ago in reply to Helen chen

Expert 1740 points

I understand about business trip.

Thank you for explaining the overcurrent limit.

In the WEBENCH Start up simulation,
The maximum input current is 23A.

This application has Vo of 10.5 V and Io of 0.5 A.

Regards,

0 Helen chen over 7 years ago in reply to watanabe

TI__Mastermind 40080 points

Thanks for the patience. TI design PMP15044 may also could meet you requirement, you can found it in the TI website.

0 watanabe over 7 years ago in reply to Helen chen

Expert 1740 points

Thank you for reply.

Is there a formula to calculate the constant of PMP 15044?

Regards,

0 Helen chen over 7 years ago in reply to watanabe

TI__Mastermind 40080 points

Do you mean the constant input current?

0 watanabe over 7 years ago in reply to Helen chen

Expert 1740 points

When applying PMP 15044 to LM 3478,
Are there any selection formulas for transformers?

0 Helen chen over 7 years ago in reply to watanabe

TI__Mastermind 40080 points

The calculation is similar. Let's talk offline. I'll send a private message to you!

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LM3478: About inrush current of LM3478.