LM51581-Q1: LM51581-Q1 IQ is too high

It looks like do not input pulse-skipping mode ,I think it should input this mode auto when load is light.

Sch and L wave

Hi Wenhe,

thank you for using the E2E forum.

Can you please mark in the schematic above where you are measuring the current.

What is the scope plot showing above? L wave = Switch node (SW) ?

Note: you still have some current through the Feedback divider and the leakage of the Capacitor.

Depending on that you will see pulse skipping

Best regards,

 Stefan

I measure voltage wave at SW node,not current .Rfb(above 0.5M) and Cout(MLCC) laekage current is very small,below 200uA,

Hi Wenhe,

sorry, do not get this.

You say "but IQ=57mA，something is wrong，IQ should below 1mA" but you measure voltage ?

I guess I have not understood your question.

Best regards,

 Stefan

I measuir voltage means i got the sw node voltage wave 

Hi Wenhe,

So the question is:

why is the current higher the 1mA?

or why do you see switching on the Switch node?

Pulse skipping starts when the output voltage is still to high when the next switching cycle starts.
As long as the output side is consuming energy more then with the minimum duty cycle does deliver on Energy, no pulse skipping is required.
Load on the output is the some of: load, current through Feedback resistor divider, output cap leakage.

Best regards,

 Stefan