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UC3525A: Uc3525 output waveform exception.

yue shang
Prodigy 180 points
Part Number: UC3525A

Please see the above  diagram & UC3525 oupput A output B waveform, The waveform is abnormal.couldn't find the cause, Can help to analyze the reason? 

Add main board schematic diagram.

  • 0
    TI__Mastermind 26745 points
    Hi Yue,

    Thanks for your interest in UC3525A. Are you able to share the power stage schematic as well? Are you running open loop?

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    TI__Mastermind 25570 points
    Hi Yue

    Can you check the OSC output to verify that the oscillator is running normally?
    I would also check the PID OUT signal and the output of amplifier
    Are you trying to use the on-board error amplifier as a unity gain buffer and have the control input come from the external error amplifier U6B ? If so then pin 1 and pin 9 of the UC3525 should be connected as you have shown but the control input from U6B should go to pin 2 of the amplifier. The connection from Vref to pin 2 is not needed.

    I would try to run the system open loop - as Ben suggested.

    Regards
    Colin
  • 0 in reply to Benjamin Lough
    Prodigy 180 points
    Dear Ben; Have Add main board schematic diagram. Please See Above. And also tested KA325. It just happens occasionally when using KA3525. So suspect it was caused by external disturbances.
  • 0 in reply to yue shang
    TI__Mastermind 26745 points
    Hi Yue,

    Thanks for the additional information. Were you able to test the circuit in open loop? Do you see abnormal behavior at the oscillator output? Do you see any noise on the IN- pin?

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 180 points

    I hvae test the circuit in open loop, The result is the same.Pls see below.

     The blue waveform is the waveform on the oscillator,It looks like there's interference on it. Can you help to check the PCB?

    ,

  • 0 in reply to yue shang
    TI__Mastermind 31580 points
    Hi Yue Shang

    Please confirm that the device is the UC3525 and not the On Semi KA3525 shown in the schematic? TI can only provide support for TI part numbers.

    Please check for noise on the SS pin and the Vcc pin. I suggest placing a 10uF, 25V ceramic on top of the part between Vcc and ground pins.

    Figure 14 shows an example layout in the datasheet, please compare this with your layout.

    Regards

    Peter