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UCC28180: 1750W Output Voltage Not Stable

Nishanth M
Intellectual 295 points
Part Number: UCC28180
Other Parts Discussed in Thread: UCC27524

Hello Team,

We have designed the 1600W PFC design using the UCC28180. We are using the same chip for the different designs like 450W, 600W & 900W works well. But in the higher power 1750W, we are facing the output voltage regulation issues. The problem starts once we load the PFC more than >600W at input of 230VAC, the output voltage will be fluctuating from 390V to 420V, and PF is coming down to <0.70. Please help me out of this problem...

Updated Values:

1. ICOMP: 1500pF

2. FREQ: 17.4K 120KHz

3. ISENSE: R 220E & C 1nF & Diode  BAS21

4. VSENSE: Top R 996K & Botto R 13K & C 1nF

5. VCOMP: Series R 16K & Series C 10uF & Parallel C 0.47uF

6. Gate Driver : UCC27524DGN & Dual Mosfets: TK110N65Z,S1F

7. Diode: C3D16065A

8. Series Diode: 1N5408

7. Output VBUS Cap: 470uF x 3

8. Input Cap: 680nF

9. Inductance: 264uH PQ5050

Kind Regards,

Nishanth M

  • 0
    TI__Mastermind 31110 points

    Hello Nishanth, 

    I will need some time to analyze your schematic diagram and circuit values to see if i can determine how the symptoms you describe can happen. 
    Please allow me a day or too to work through this. 

    Regards,
    Ulrich 

  • 0 in reply to Ulrich Goerke
    TI__Mastermind 31110 points

    Hello Nishanth, 

    I am a little confused by your initial statement of having designed a 1600W PFC and then testing it at 1750W, but that does not really affect the main issue. 

    I did not see any significant problems in your schematic diagram, even accounting for the list of value changes (above). 
    However, I do see that C109 = 220pF on the input of U14 (UCC27524 gate driver) will have an R-C time constant with R153 = 1kR of ~220ns.
    Since the low-going threshold is 1V and the signal has to come down from 12V, this RC adds about 1us delay to turning off the MOSFETs. 

    At 230Vac input, the delayed turn-off allows higher peak current in the inductor.  Please check to see if your inductor current shows signs of saturation.

    ==>  In any case, please remove C109 completely.  There should be no turn-off delay, so that the PWM can keep adequate control over the inductor current. 

    One other concern I have is that the current sense resistance = 0.02R/3 = 0.006667R.  This value is too low for 1750W. 
    I recommend to remove ONE of R162, R158, and R168 so that effective Rs = 0.010R.  
    Be sure to re-evaluate the maximum power dissipation in the remaining two resistors (or use 0.03R/3).  

    Regards,

    Ulrich

  • 0 in reply to Ulrich Goerke
    Intellectual 295 points

    Hello Ulrich,

    Thanks for the support.

    1600W is the MAX load at PSFB side but we designed the PFC for 1750W. Apologies for the confusions...

    We will check it and feedback you after removing C109 and making Current sense as a 0.01R asap. 

    As you said the current sense should be 0.01R but ICOMP is >5.7V saturation mode. Our Nominal Working voltage is 230VAC 50Hz. If we go above the 1500W, the ICOM is going to saturation mode, so how to avoid the ICOMP saturation mode? 

    Please help out of this problem and give us the solution...

    Kind Regards,

    Nishanth M

  • 0 in reply to Ulrich Goerke
    Intellectual 295 points

    Hello Ulrich,

    We tried removing the C109 & making Current Sense to 0.01R. The problem remains same above >300W. We tried the method as you said in other thread that adding resistor across the ICOMP capacitor. We added from 47K & 100K but the PF is going down from 0.92 to 0.68 and voltage is not constant. Currently we mounted only one Mosfet. So please check and help me out of this issues....

    Gate Waveform at Mosfet:

    ICOMP Pin at without Load at 390V:

    ICOMP Pin at Load of 300W at 390V:

    VSENSE PIN:

    Kind Regards,

    Nishanth M 

  • 0 in reply to Nishanth M
    TI__Mastermind 31110 points

    Hello Nishanth, 

    When showing waveforms please always include the full test conditions for each waveform. 

    In your first screenshot, the duty cycle variation looks mostly okay except the long dead time (when Vgs = 0V) indicates that input voltage does not reach 0V.
    I assume that this is 230Vac input and no-load output condition.  With no-load, Cin would hold a charge and duty cycle would not reach near 98%.
    Higher loads should increase the max D to close to 98%.

    Your second screenshot of ICOMP is okay, but does not convey much information. 

    Your fourth screenshot of VSENSE shows 5.286V which is about 5.7% high with respect to the 5.0V internal reference.  Was this captured just after a load-drop to 0W when the output had an overshoot?  

    Your third screenshot of ICOMP with 300W load uses 200ms/div sweep.  This means there are 10 line cycles per division and the information is all crowded together.  In addition, the sample rate (5kS/s = 0.2ms/sample) is so low that aliasing may be distorting the signal.    

    I suggest to view ICOMP at 5ms/div sweep and a much higher sample rate.  
    Also, can you capture the actual input current waveform when the problems occur (and list the specific test conditions)?

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    Intellectual 295 points

    Hello Ulrich,

    Thanks for the Great support.

    We finally solved the problem at last week. We reduced the GND track length of the VCOMP Cap Ground and IC GND. Changed the VSENSE Cap to 100pF from the 1nF Now the output voltage is constant and PFC also comes to 0.999 and very stable operation. Check out the below current waveforms at the input AC side.

    Test Condition:

    AC input Voltage: 230V 

    AC input Frequency: 51Hz

    AC input Current: 6.315A

    Output VBUS Load Type: Resistive

    Output VBUS Voltage: 385V

    Kind Regards,

    Nishanth M