LM25145: FET operation problem

Minsu Park

Prodigy 60 points

Part Number: LM25145

Tool/software:

Hi Sir,

High-side FET and low-side FET behavior is strange.

Low side FET gate wave

High side FET gate wave

Circuit diagram

Could you please check the problem and tell me how to fix it?

6 months ago

0 Dino Maslic 6 months ago

TI__Expert 5190 points

Hi Minsu,

Can you please fill out the quick start calculator found on the website for this product? This way we can have all the information we need regarding your application.

Thanks,

Dino Maslic

0 Minsu Park 6 months ago in reply to Dino Maslic

Prodigy 60 points

Hi,

I've attached the file you requested.

6864.LM25145_quickstart_calculator_A5.xlsm

Regards,

Minsu

0 Dino Maslic 5 months ago in reply to Minsu Park

TI__Expert 5190 points

HI Minsu,

Schematic looks fine to me, could you send your all layers of your PCB's layout so I can take a look at it?

Thanks,

Dino Maslic

0 Minsu Park 5 months ago in reply to Dino Maslic

Prodigy 60 points

Hi,

Capture and upload the PCB layout.

Layer1

Layer2

Layer3

Layer4

Please review.

Regards,

Minsu

0 Dino Maslic 5 months ago in reply to Minsu Park

TI__Expert 5190 points

Hi Minsu,

Thanks for sending the layout over, I will discuss this with my team and get back to you as soon as I can.

Thanks,

Dino Maslic

0 Minsu Park 5 months ago in reply to Dino Maslic

Prodigy 60 points

Hi,

When can I get an answer?

Thanks,

Minsu Park

0 Dino Maslic 5 months ago in reply to Minsu Park

TI__Expert 5190 points

Hi Minsu,

Thank you for your patience.

Looking through the layout I found some critical errors with the routing of gate drive signals. You should not have the HO/LO signals on the same board layer as SW as it can cause problems with the operation of the device. We recommend putting SW on a separate layer from HO/LO separated by a ground plane. Please review Section 11 of the datasheet which highlights layout practices that should be followed.

Thanks,

Dino Maslic

0 Minsu Park 5 months ago in reply to Dino Maslic

Prodigy 60 points

Hi,

I worked as shown in the photo below, referring to the answer, but there was no improvement.

I would like to request further review.

Thanks,

0 Dino Maslic 5 months ago in reply to Minsu Park

TI__Expert 5190 points

Hi Minsu,

Both of the gate drive signals should not be on the same layer as SW, looking at the picture above, LO and SW are on the same layer. Please ensure they are not on the same layer.

Thanks,

Dino Maslic

0 Minsu Park 5 months ago in reply to Dino Maslic

Prodigy 60 points

Hi,

I will explain the review process.

1. Cut the LO pin wiring on the PCB

2. Connected LM25145RGYR pin 13 (LO) and Low side FET Gate pin with a separate wire.

3. I connected it avoiding the SW wiring.

4. There is no improvement in operation.

I would like to request further review.

Thanks,

0 Dino Maslic 5 months ago in reply to Minsu Park

TI__Expert 5190 points

Hi Minsu,

Just to confirm what you are saying, are you using an external wire to connect to the FET or a trace on the PCB?

Please confirm.

Thanks,

Dino Maslic

0 Minsu Park 5 months ago in reply to Dino Maslic

Prodigy 60 points

Hi,

I have attached a captured photo.

I would like to request further review.

Thanks,

0 Dino Maslic 5 months ago in reply to Minsu Park

TI__Expert 5190 points

Hi Minsu,

Using an external wire to power the gate drive will provide much worse performance. In order to properly change the routing of the gate drive signals, there would need to be a revision in your board's layout. Please do so following above recommendations and recommendations in the datasheet.

Thanks,

Dino Maslic

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LM25145: FET operation problem