LM3478: Startup problems

Shuji Ishiwata

Part Number: LM3478

Hi All,

I have a question about the LM3478.
My customer is designing a circuit that can step-up and step-down. The customer has designed the following circuit based on a simulation circuit on webench.

This circuit may not work correctly. It will not work if the load current is changed.
VIN=6V
VOUT=24V

It also does not work correctly when it is operated under the following conditions.
VIN=38V
VOUT=24V

What are the possible causes?
In the webench simulation, VIN=6-38V / VOUT=24V / IOUT=0.1A.

Best Regards,
Ishiwata

over 1 year ago

0 Brigitte over 1 year ago

TI__Guru 58225 points

Hello Ishiwata,

Why has VIN such a specific shape? It seems that during startup with higher load, VIN does not reach the final value, so is it possible that there is a current limit on the source?

Best regards,
Brigitte

0 Shuji Ishiwata over 1 year ago in reply to Brigitte

Genius 5905 points

Hello Brigitte,

Thanks for your reply, I appreciate it.

The input is doing current limiting.
The customer says that if the limiting current is not done, the source current will continue to flow.
We have not yet confirmed its maximum value.

Best Regards,
Ishiwata

0 Shuji Ishiwata over 1 year ago in reply to Shuji Ishiwata

Genius 5905 points

Hello Brigitte,

Are there any details that you can ask your clients to verify?
We look forward to your support.

Best regards,
Brigitte

+1 Haroon Wardak over 1 year ago in reply to Shuji Ishiwata

TI__Genius 10375 points

Hi Shuji,

Thank you for your reply, if the source is limiting the current and that limitation is hindering the start-up for the device. The device needs certain power from the source and if the source limits that power the device will not be able to start-up properly.

Hope this resolves your questions.

BR,

Haroon

0 Shuji Ishiwata over 1 year ago in reply to Haroon Wardak

Genius 5905 points

Hi Haroon ,

Thank you for your reply.
Increased the current limit of the power supply input to the LM3478. As a result, it worked fine.
I found that the cause was the current limit of the stable power supply.
Thank you for your support.

Best Regards,
Ishiwata

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LM3478: Startup problems