LM3492: LM3492/-Q1 in discontinuous mode

Artiom Orlov

Part Number: LM3492

Hi there,

We had some ICs (LM3492/-Q1) failures on a customer's site. Just wondering how well this IC can handle discontinues mode if used with light loads?

Thanks

over 3 years ago

0 Irwin Nederbragt over 3 years ago

TI__Mastermind 28655 points

Hello,

It is not recommended to run in discontinuous mode, see page 21, 9.2.2.2. It should not damage the LM3492 but it will not be optimal operation.

Best Regards,

0 Artiom Orlov over 3 years ago in reply to Irwin Nederbragt

Prodigy 40 points

Hi Irwin,

Thanks for your reply. That info in 9.2.2.2 only states how to calculate the inductor in CCM. That's clear for me. The only question, is there any possibility to damage ICs in that mode? and why do you think this won't be optimal operation?

Cheers

0 Irwin Nederbragt over 3 years ago in reply to Artiom Orlov

TI__Mastermind 28655 points

Hello,

It should not damage the IC running in discontinuous mode. The internal compensation is set for continuous conduction mode. How are the ICs failing, any particular operation mode?

Best Regards,

0 Artiom Orlov over 3 years ago in reply to Irwin Nederbragt

Prodigy 40 points

Three PCBs were connected in parallel (one IC per one PCB), running at 24-27V input. Output 35V, in sort of beacon mode (2 strings are flashing). It's not yet confirmed what actual LOAD (flash pattern) the customer was using while it failed. I just wanted to make sure that DCM could/could not cause that issue.

These three ICs failed at the same time, although they are on separate PCBs and only sharing input power. TVS diodes were still functioning.
Can't think anything else why it should fail.
I would appreciate any guidance.

Thanks

0 Irwin Nederbragt over 3 years ago in reply to Artiom Orlov

TI__Mastermind 28655 points

Hello Artiom,

Have they been testing these boards for a while? It seems strange that they all failed at the same time. Can you check to see if the peak current sense is below the inductor saturation current?

Best Regards,

0 Artiom Orlov over 3 years ago in reply to Irwin Nederbragt

Prodigy 40 points

Irwin,

Yes, it was odd for me as well. The customer said they have been running the boards for a while. The Ilim resistor is 13K , but inductor's saturation current is 3.5A. So I_lim is way lower.

0 Irwin Nederbragt over 3 years ago in reply to Artiom Orlov

TI__Mastermind 28655 points

Hello Artiom,

It seems something must have happened for them to fail at the same time such as the power source did something. Is this the only time they failed (the three boards)?

Best Regards,

+1 Artiom Orlov over 3 years ago in reply to Irwin Nederbragt

Prodigy 40 points

Hi Irwin,

As far as I am aware of, only these 3 failed amongst >1000 units. This is very rare or only occasion when all 3 PCBs failing at the same time.
My guess is as yours - it should something happened on power source side.

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LM3492: LM3492/-Q1 in discontinuous mode