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UCC28700 Output Current

Ye-sheng Kuo
Prodigy 240 points
Other Parts Discussed in Thread: UCC28700

Hi,

  I'm following the PMP8286 (http://www.ti.com/tool/pmp8286) without the secondary USB charging. However, when I try to source 150~200 mA from the output, the voltage start dropping like this.(from 5.2 V to 2.8 V) 

Therefore, the output current cannot sustain at 150~200 mA. If I increase the load above 200 mA, the circuit works just fine. The output holds at 5V. Any idea?

Thanks!

  • 0
    Intellectual 425 points

    Hi;

    UCC28700 can give min 1Watt and max 20Watts.

    I guess the issue is related to this.

    try adding a bleeder resistor to the output

  • 0
    TI__Guru* 86266 points

    That design came from the elab you might want to check with them to see what the minimum load requirement is for their design.  I don't believe the elab engineers support the forum.

    Regards,

     

  • 0 in reply to nemenem
    TI__Guru* 86266 points

    The control IC does not limit the power in this application.  Theoretically you should be able to design for 20W using this control IC.

    Regards,

  • 0 in reply to Mike O'
    Prodigy 240 points

    If you look at PMP8286 or datasheet, the current sense resistor limits the maximum current output. In this application, it should provide 10 W max only. However, in my experiment, I went to 12 W but the output still not cut-off.

    For the low-loading problem, I solved this by increasing the current sense resistor. According to the tools or datasheet provided, the Rcs = 1 ohm if you want to source 2 A maximum. I increased to 1.3 ohm and the low-current voltage drop goes away.