LM3429-Q1: Gate rise a pulse

Kami Huang60

Part Number: LM3429-Q1
Other Parts Discussed in Thread: LM3429

Dear Sir/Ms.

My client reported that their switching frequency would under certain circumstances change from 400Khz to half of 200Khz. I directly ask the customer to measure the inductor current and Vgs, and I see that Vgs has this kind of waveform when something goes wrong.
Have you ever encountered this problem? In which direction can I suggest customers to start looking for?

Normal

Ch1 Vgs, Ch 4 IL

Not Normal

Best Regards,

Kami Huang

over 3 years ago

0 Tuan Tran74 over 3 years ago

TI__Genius 17690 points

Hi Kami,

I did not get any scope capture or schematic attachment from you or operating condition.

Thanks Tuan

0 user6377930 over 3 years ago in reply to Tuan Tran74

Prodigy 30 points

Hi Tuan,

Please see the picture below

Normal

Ch1 Vgs, Ch 4 IL

Not Normal

Ch1 Vgs, Ch 4 IL

0 Tuan Tran74 over 3 years ago in reply to user6377930

TI__Genius 17690 points

Kami,

I did not get the schematic. From the scope capture it can be instability or something else in layout.

Thanks Tuan

0 Kami Huang60 over 3 years ago in reply to Tuan Tran74

Genius 3830 points

Hello Tuan,

I also think this is a phenomenon caused by Layout, Could you please help me check at the schematic, is it possible to adjust the value of the parts to improve this phenomenon?. Attached file is customer's LM3429 schematic. Please give us some advice.

Best Regards,

Kami Huang8267.Schematic Prints.pdf

0 Tuan Tran74 over 3 years ago in reply to Kami Huang60

TI__Genius 17690 points

Hi Kami,

Please short out R13 to zero Ohm to see if it improves the gate drive capability.

Thanks Tuan

0 user6377930 over 3 years ago in reply to Tuan Tran74

Prodigy 30 points

hi Tuan

I am a KAMI customer

We have received your suggestion, and its condition has not improved after testing

I don’t know if you have any other suggestions that can assist us and improve its efficiency

Thanks

0 Tuan Tran74 over 3 years ago in reply to user6377930

TI__Genius 17690 points

Hello,

It looks like the gate drive slew rate is quite slow and that's why I recommend shorting out the 15 Ohm gate resistor. You will need to find a FET that is of lower gate charge so it can switch faster or lower the switching frequency.

Thanks Tuan

0 user6377930 over 3 years ago in reply to Tuan Tran74

Prodigy 30 points

Hi Tuan

As shown in the attached picture, the result of following your instructions looks very bad

Ch1 Vgs，Ch 4 IL

Do you have a recommended model for replacing MOS?

Thanks

0 Tuan Tran74 over 3 years ago in reply to user6377930

TI__Genius 17690 points

Hello,

We do not recommend a FET replacements for your particular design. We recommend that you look at our evaluation board for both design and layout consideration. We would also recommend that you get an eval board if you have issue.

www.ti.com/.../LM3429BKBSTEVAL

Thanks Tuan

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LM3429-Q1: Gate rise a pulse