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Original question:

UCC25600: UCC25600D Capabilities for Battery Charger Application

UCC25600: PMP11282: Support Required: Support Required – Issue with PMP11282 Rev A Reference Design

Anand Matta
Prodigy 130 points
Part Number: UCC25600
Other Parts Discussed in Thread: PMP11282

Tool/software:

Dear TI Team,

I am working on the reference design PMP11282 Rev A, which is implemented on the PMP11064 Rev B PCB. I am currently facing an issue with the LLC IC UCC25600D, where it is not regulating properly at startup.

For testing, I am applying an input voltage of 80–90 VAC, 50 Hz.
The LLC half-bridge resonant converter is designed for a 24 V regulated output, but I observe that the output initially rises to 32 VDC and then gradually reduces back to 24 VDC. At this stage, only the output capacitors are connected, and no load is applied.

  • Blue signal: Output voltage (~375 VDC)

  • Yellow signal: Output voltage (initially 32 V, gradually reducing to 24 V)

Could you please confirm how much minimum load is required for stable regulation? Also, I would appreciate your guidance on how this issue can be resolved.

Please find the schematic and DSO waveform photo attached for reference.

Best regards,
Anand Matta

400 Watt Half Bridge LLC.pdf

  • 0
    TI__Intellectual 2405 points

    Hi Anand,

    Looks like the feedback is not properly tuned.

    Allow me some time to look into the reference design.

    Meanwhile can you please confirm , are you implementing the same reference design or any modifications done?

    Regards,

    Yamini.

  • 0 in reply to SIRIPURAM YAMINI
    Prodigy 130 points

    Hi Yamini,

    Yes, I am currently using the same reference design.
    During testing, I observed that the LLC regulates at 20.14V up to 3.6 A load. Beyond this point, it stops regulating and the output voltage drops to around 3.5 V.

    Could you please guide me on how to resolve this issue?

    Best regards,
    Anand Matta

  • 0 in reply to Anand Matta
    TI__Intellectual 2405 points

    Hi Anand,

    Sorry for the delay.

    Can you please check whether GD1 and GD2 pulses are coming when the output voltage is dropping.

    Regards,

    Yamini.

  • 0 in reply to SIRIPURAM YAMINI
    Prodigy 130 points

    Dear Ma’am,

    Please find attached the DSO screen captures for the following scenarios:

    1. Output at 20 V with load – Operating frequency observed: 162 kHz
    2. Output at 32 V without load – Operating frequency observed: 344 kHz
    3. Output at 6 V with load – Observed that the low-side MOSFET is not switching

    In each case, I have measured the transformer primary winding current along with the switching waveforms of both the high-side and low-side MOSFETs.

    AC input current: ~0.3 A (measured with clamp meter, before bridge rectifier)

    DC output current: ~1.4 A @ 20 V (measured with clamp meter)

     

    Kindly review the attached results and advise on possible causes or next steps.

    Please find the attached schematic for your review.TI Reference.pdf

    The output feedback loop appears to follow a Type III compensator design; however, I noticed that the 21.5 kΩ resistor in parallel with the 2700 pF capacitor are additional components.

    Could you please share the calculations for the pole and zero frequencies, along with the corresponding feedback component values (R515, C100, C529, C530, R534, R526)?
    Please find the attached screenshot for reference.

    Also, could you clarify the purpose of the current sharing control—is it intended for parallel operation, constant current (CC) mode, or overcurrent shutdown?

    Best Regards,
    Anand Matta

  • 0 in reply to Anand Matta
    TI__Intellectual 2405 points

    Hi Anand,

    May I know your application, if your power level is 400W, I suggest you to look UCC25661x (half bridge LLC controller) parts.

    Please let me know you have any questions on it .

    Regards,

    Yamini.

  • 0 in reply to SIRIPURAM YAMINI
    Prodigy 130 points

    Dear Ma’am,

    I would like to try using this controller for the power supply application in avionics.
    Initially, I plan to complete the prototype for the 400 W version, and later scale it up to 900 W – 1 kW.

    Regards,
    Anand

  • 0 in reply to Anand Matta
    TI__Intellectual 2405 points

    Hi Anand,

    For the mentioned application you can use UCC25661x which will support both 400W and 1kW power levels. Also, it has improved control technique and protection features.

    UCC25661

    ucc25661.pdf

    A new revision for the above datasheet yet to publish on the website, you can use the attached datasheet.

    Regards,

    Yamini.