• State
  • +1 person also asked this people also asked this
  • Locked Locked
  • Replies 5 replies
  • Subscribers 66 subscribers
  • Views 228 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UCC25660: UCC25660 Feedback Circuit and Protection Mechanism

noah LIN
Prodigy 51 points
Part Number: UCC25660
Other Parts Discussed in Thread: UCC28180, UCC24624

Tool/software:

HI ALL

We are currently designing a 1000W AC/DC system using a PFC UCC28180 + LLC UCC256604 without HV startup + SR UCC24624 configuration.

The design specification for Vout is 40V/25A.

Due to an initial issue with load extraction, we adjusted RISNS from 205 ohms to 68 ohms, which allowed us to successfully add a load of approximately 40V/1.5A (60W). However, when I attempted to increase the load to

2.5A (100W), the protection mode was triggered.

What aspects can be checked? The VFB voltage is approximately 3V under no-load conditions.

Reducing the resistance will lower the slope of VFB vs. Pin, is this approach correct?What slope (ratio) is correct?

sch_adp1000a_e20_20241109.pdf6153.UCC25660x_CALC_1.0_Noah.xlsx

How can I ensure that the VFB setting is correct and that it does not enter OCP, OLP, or burst mode?

Thanks f

Regards

  • 0
    TI__Intellectual 1730 points

    Hi Lin,

    Your query is under review.

    I will get back to you in a day.

    Regards
    Hemanth

  • 0 in reply to Hemanth Sreeperumbudur
    Prodigy 51 points

    Hi Hemanth

    To clarify a few points:

    1.There is a strange phenomenon: when I hook the oscilloscope probe onto pin 1 of the VO618A, the load capacity can increase to 160W. (Only the probe needs to be connected; the oscilloscope itself is not required.)

    2.When I measure the 390V output voltage point of the PFC, I observe that under load conditions, whether it starts up successfully or fails to start, the 390V instantly drops to around 360V–370V. Is this normal? How can this be improved?

    3.So I attempted to adjust and lower the BLK voltage, bringing VBLKStart down slightly to around 350V. However, the load startup became very unstable—sometimes it outputs continuously, while other times it outputs briefly before going into protection mode. Could you suggest what I should check?

    4.Finally, I'm quite curious about one thing: as the load varies from 0 to 1000W, what exactly changes in VFB? And how is the protection point set?

    Thanks

    Regards

    Noah

  • 0 in reply to noah LIN
    TI__Genius 13845 points

    Hi Noah,

    Here are few suggestions:

    1. Could you debug LLC only by Directly supplying DC input at the LLC input. Apply 15V at the VCC pin of the IC. That way its easier to identify the issue.

    2. Could you figure out which fault is being triggered: OPP, OCP, OVP, UVP? Capture, ISNS,HS,Vout, Iopto (voltage across 10k resistance that's connected in series with transistor of the opto as shown below.)

    3. As you increase the power output, the FBReplica should increase. You can measure FBReplica as shown below.

    At lowest input voltage and at the maximum output power, The FBReplica should be below OPP threshold (4.75V).

    Please use the updated calculator which is in TI.com where TSET resistor values were updated.

    Regards

    Manikanta P

  • 0 in reply to Manikanta Pallantla
    Prodigy 51 points

    Hi Hemanth

    According to your suggestion, I have readjusted option #7 in TSET with an appropriate resistance value and have also modified the RISNS resistance value to 160K

    However, when drawing a 260W load, instability occurs at 390V, as shown in the attached image.

    Could this be more likely due to a triggered protection mechanism, or is it an issue with the PFC output?

    Thanks

    Regards

    Noah

  • 0 in reply to noah LIN
    TI__Genius 13845 points

    Hi Noah,

    As I mentioned before, you need to debug only LLC. Please share the waveforms of each signal that I asked before.

    Regards

    Manikanta P