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UCC25600: PMP8920REVA_02: Reference Design with problem

Part Number: UCC25600
Other Parts Discussed in Thread: PMP8920, , UCC24610

I adapted my PSU from the PMP8920 project ( My project uses 220VAC @ 60Hz at the input and needs 12V @ 10A (120W) at the output. I'm using the (UCC25600 + UCC24610) equal to the reference design mentioned.

However, when I have low output power (between 0.4A to 2.5A), the UCC25600's "GD1 and GD2" pins and the UCC24610's "GATE" pin become unstable.

The source does not drop, but the output ripple is high. Before 0.4A and after 2.5A the source works perfectly.

What could be happening? Problem with UCC25600 or UCC24610 circuits?

Thank you guys!

  • Hi Hernani,

    Thank you for your interest in UCC25600. What is the switching frequency at the edge of the instability region at 0.3A and 2.6A load? Could you share some waveforms of the gate drive instability? How much ripple do you see at the output when the gate drive is unstable? It sounds like the device might be in burst mode. You could try limiting the switching frequency to less than 350kHz which would disable this mode.

    Best Regards,
    Ben Lough
  • Hi Hernani
    I'd suggest that you disable the SR driver and use diode rectification. This will let you see if the problem is due to the SR controller being unable to detect when to turn the SRs on and off correctly at low currents.
    What is the instability at GD1 adn GD2. Do they operate at a relatively fixed frequency and 50% duty cycle or is the duty cycle reduced ? Also, does the frequency reach the 350kHz limit at which the controller stops the outputs. This behaviour is under the control of the FB pin so look at the levels there.
    Finally, the SR controller in particular will be very sensitive to PCB layout - it has to detect very low voltages across the SR drain/source and it won't be able to do this if the layout parasitics are introducing noise.

    Anyhow - first disable the SR drivers and see what happens.

  • Hi, Benjamin.

    Waveforms are attached.

    I used infinite persistence to the measurements.

    Apparently, the frequency remains around 100 kHz, but there is a duty cycle change in both circuits.

    Best Regards,


  • I wonder if this also happens in the PMP8920REVA design?