LM3481-FLYBACKEVM: SW node jitter when working on DCM with no-load

Jack CCY

Intellectual 1695 points

Part Number: LM3481-FLYBACKEVM
Other Parts Discussed in Thread: LM3481

Hi sir,

I tested LM3481 FLYBACK EVM recently and found that when there is no load, the Vds(SW) node voltage will shake.

I added some load like 0.2mA. there will be no jitter.

I wonder why this happened?

Thank you

over 8 years ago

0 Youhao Xi over 8 years ago

TI__Guru* 78430 points

All peak current mode controlled circuit is vulnerable to jitter at no loads: the current signal is barely above the ground floor. You can consider to increase the current sense resistor to improve the noise immunity.

0 Jack CCY over 8 years ago in reply to Youhao Xi

TI__Intellectual 1695 points

Thank you. But why the peak current control is vulnerable to jitter at no loads? Would you please explain it with detail?
Thank you so much

0 Youhao Xi over 8 years ago in reply to Jack CCY

TI__Guru* 78430 points

In peak current mode control, the duty cycle is obtained by comparing the peak current and error voltage. At light load, the peak current becomes very small and ground noises can easily affect the PWM comparator performance.

0 Jack CCY over 8 years ago in reply to Youhao Xi

TI__Intellectual 1695 points

OK. Thank you so much.

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LM3481-FLYBACKEVM: SW node jitter when working on DCM with no-load