PMP41009: UCC28740-Q1

Hi Shilin, 

What's the output voltage and output current for your design? What's the output current and voltage for the waveform?

Hi Linda,

CH1 is the output1(about 15V\0.3A)，CH2 is the output 2(about 12V\0.125A)

Could you share the schematic? Did you power up it with no load? what's the input voltage? what are the waveforms for the there channels?

Hi Linda

I connected an LDO after the 12V output(CH2), and CH3 is the output of LDO.

yes I power up it with no load.

The switching frequency is stable when unloaded.

The schematic is showen below.(The actual resistance and capacitance values on the board may differ slightly from the schematic)

The output capacitance is too small, it may cause the control loop unstable, please test the bode plot.

Hi Linda

Thanks for the reply. And another question:How should i test the bode plot? Are there any user manual or other things to refer?

Thank you again

Do you have Bode 100, AP300 or other network analyzer? If haven't, you can't test the bode plot. But we also can test the load transient, the following image for your reference.  Another way is to add more output capacitor and check the SW waveform.

I might be able to borrow bode 100, but can not sure.

I'll try to increase the output capacitance. Do you have an estimate value of the capacitors to add?

Thank you Linda

You can try 300uF