LM5166: Power supply light load noise

Jojo Wang

Part Number: LM5166

Hi,

I have a BUCK design working in a light-loaded burst mode operation with audible noise.Some FAEs recommend the following circuits to reduce noise.

I don't understand why this works. Looking forward to your answer.

Jojo

over 4 years ago

0 Andy Chen over 4 years ago

TI__Mastermind 27045 points

Hi Jojo,

a RT resistor connected between RT pin and GND enables COT mode operation, PFM mode is disabled by this way which may cause audible noise because of burst mode switching.

0 Jojo Wang over 4 years ago in reply to Andy Chen

Prodigy 150 points

Hi Andy,

What functions do these components (Ca, Cb, and Ra) play in the circuit?

0 Andy Chen over 4 years ago in reply to Jojo Wang

TI__Mastermind 27045 points

Hi Jojo,

Pls refer to LM5166 data sheet Table2 on page 19, COT control mode require adequate ripple information injected on FB pin, Ca/Cb and Ra is Type 3 ripple injection circuit for lower output ripple.

0 Jojo Wang over 4 years ago in reply to Andy Chen

Prodigy 150 points

Hi Andy,

Thank you for your comments. Due to your patient guidance, I gradually understand the circuit principle. Its work at light loads does reduce the output voltage ripple. But I still have some confusion about this circuit working under heavy load.After all, its FB pin introduces the SW voltage signal. What is the performance of the circuit under heavy load conditions?

0 Andy Chen over 4 years ago in reply to Jojo Wang

TI__Mastermind 27045 points

Hi Jojo,

Pls send me email at andy.chen@ti.com, I will send you some document for your better understanding the principle.

I will close this thread.

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LM5166: Power supply light load noise