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UCC28950: UCC28950

A.S.Bhushan
Expert 1060 points
Part Number: UCC28950

We designed DC_DC converter using UCC28950. 

Vin:200-240VDC,                         Vout: 22 to 26VDC, 17A output. Working fine.

 But, At Vin 200VDC and at Vout 26VDC, when output no load it gives 26VDC. fine

but, the moment when i put 2A load, output voltage drops to 23.5V and output slowly increases to 26V after 3 minutes.

I adjust error amplifier / compensation circuit , but no use.

Here i am using transformer turn ratio 7 and inductance of primary was 1.6mH, Output capacitance: 4500uH and input capacitance 1400uH

and output inductor value is 15uH.

Here i am attaching schematics also. Please suggest us to solve this problem.SCHEMATIC _ 02.CONTROLLER.pdfSCHEMATIC _ 01.POWER STAGE.pdf also

  • 0
    TI__Mastermind 25570 points

    Hello A.S.

    I would expect that the converter would operate correctly in this condition so what you are seeing is definitely strange.

    A few things you should check

    Check VREF remains at 5V -

    Check that the CS signal at the CS pin of the IC is 'clean' - I'd suggest  you use a 'tip and barrel' measurement technique for this

    Your CS filter Capacitor should be at the CS pin with a low impedance connection to the GND and the filter resistor should be close to the CS pin too.

    /cfs-file/__key/communityserver-discussions-components-files/196/Tip-and-Barrel.pptx

    Can you send me a plot showing how Vout recovers - 500ms per division for example

    Can you send me a plot of the OUTA, OUTD and SYNC signals - one at 500ms/div, another at 20us/div and another at some intermediate rate so that I can see if the system is running in burst mode.

    It would also help if you can send me your Gerber files - I'm at colingillmor@ti.com  

    It's always possible that there is some interference getting onto the EA- or COMP lines.

    Regards

    Colin

  • 0 in reply to Colin Gillmor
    Expert 1060 points

    Hi Mr. Colin,

    Thanks for your information. The problem has been solved.

    What ever you suggested regarding CS signal, we rerouted the layout.

    Now problem solved. Thank you so much