LM3404: Fsw decreases significantly

Liu Yang

Part Number: LM3404

Hi team,

When the PCB with LM3404MR/NOPB is not installed and it is operated by a DC power supply and a function generator, it operates as designed, but when the board is installed in the product, Fsw decreases significantly.
In this case, which pin should I focus on and improve?

The attached is wave form

SW output voltage.pptx

Beat Regards,
Tom Liu

over 3 years ago

0 Irwin Nederbragt over 3 years ago

TI__Mastermind 28655 points

Hello Tom,

If it has the same input voltage, the same LED load and the same PWM signal it should operate the same.

What is the power source 'in the product'?

What is Vin in the product, Vled the inductor value you are using and Ron (both cases).

Best Regards,

0 Taku Kato over 3 years ago in reply to Irwin Nederbragt

Prodigy 90 points

Hi Irwin,

thank you for helping me.

Vin is 12V.

The power source in the product is the AC/DC unit parchaced from a dedicated manufacture.

It guarantees to provide 12V constantly. And I have already checked voltage at Ron, it was 12V.

Ron is 910 k orm.

Inductor is 33 uH.

BR,

Taku Kato

0 Irwin Nederbragt over 3 years ago in reply to Taku Kato

TI__Mastermind 28655 points

Hello,

Have you looked at the output voltage and current?

If Vin is the same, Vout is the same and the PWM signal is the same it should operate the same. Are you doing anything different between outside of the product and inside the product?

Best Regards,

Power management

Power management forum

LM3404: Fsw decreases significantly