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UCC28910: 30mA to 100mA the output voltage drop from 4.2v to 3v

Joseph zheng
Prodigy 30 points
Part Number: UCC28910

hi

have some question about UCC28910，thanks a lot for helping me.

describe ：

1、 i use UCC28910 input 220v AC， and output is 4.2v， the shcematic as below

2、the load of output is for MCU module，usual the current is 30mA，but when the RF-ZigBee module work， the current up to 100mA

3、when the current 30ma up to 100ma the ouput voltage has a short drop, from 4.2v to 3v. and the test as below, the red is output voltage， the blue is Vs

question:

1、What caused the voltage drop ？

2、I guess that UCC28910 work on DCM （when current is 30ma） ，and normal mode（when 100ma）.

     so how long does DCM change to normal mode ？ what will affect the time ？

     and what is the transfer function model？

 

thanks very much

and best regards

       

  • 0
    TI__Expert 7395 points
    Joseph,
    Thank you for your interest in TI here. I'll have an applications engineer comment in depth to your questions soon. Please excuse any delay as Monday is a holiday for many in the US.

    Ucc28910 is a DCM controller and will run in TM/DCM in all conditions.

    As a general debug reference please see our debug guide for PSR controllers here: www.ti.com/.../slua783.pdf

    If you can, can you include more complete schematic with the transformer connections as well?

    You mention one signal is Vs. please do not probe Vs directly if you are. It's very sensitive to noise and capacitive filtering even from scope probes and will affect the converter performance. It's best to measure the aux winding signal instead for that information. Please do provide that measurement so we can view the switching performance.

    Regards
    John