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UCC21520: UCC21520 Break

Alex Chen9
Expert 1075 points
Part Number: UCC21520
Other Parts Discussed in Thread: UCC2895, , UCC3895

hi Sir

I Desgin a DC source about 1.2kw, which DCDC is ucc2895 for full bridge, the G-driver is ADI-ADUM4223, The system is stable

but, when i change the g-driver to the UCC21520, the system unstable,

about the detail describe,please refer to the attach of files

please advise it,thanks

ucc21520.docx

  • 0
    TI__Mastermind 28960 points

    Hello Alex,

    I am an applications engineer supporting UCC21520. There are several differences when comparing UCC21520 to ADUM4223:

    • Peak current for ADUM4223 at 15V supply voltage (5.5A source, 7A sink, refer to figure 18 in ADUM4223 datasheet) will be higher than UCC21520 at 15V (4A source, 6A sink) because UCC21520 provides the same peak current regardless of supply voltage. The gate resistors may need to be decreased for UCC21520 to compensate for this difference.
    • Propagation delay for ADUM4223 is typically 40ns, whereas propagation delay for UCC21520 is typically 20ns. There may be delays in the PWM control loop which must be adjusted to account for this difference.
    • UCC21520 has an integrated dead time feature which on your attached schematic is programmed to a constant minimum of 200ns. Is this similar to the dead time behavior programmed by the UCC2895 ADS/DELAB/DELCD pins for ADUM4223? Normally ADUM4223 has no dead time feature.

    Can you help me to understand what you mean by "unstable?" For example, is the transient response poor? Is the output oscillating?

    What is the switching frequency?

    What are the resistor values on the ADS/DELAB/DELCD pins?

    Regards,

  • 0 in reply to Derek Payne
    TI__Guru**** 189399 points
    Hi Alex,

    It's been a while since we've heard from you, so we must assume you've resolved your issue.

    If possible, please post how it was resolved for others to learn from.

    If not, let us know, and we will work with you to resolve it.
  • 0 in reply to Don Dapkus
    Expert 1075 points
    The issue still exist. Customer already change to use ADI/ADUM4223
  • 0 in reply to Don Dapkus
    Expert 1075 points
    can you share the gate resistors between the UCC2895 with UCC21520?
  • 0 in reply to Alex Chen9
    TI__Mastermind 28960 points
    Hi Alex,

    I am not sure I understand when you say "share the gate resistors." The output of UCC2895 should be used to drive the input of UCC21520, and the outputs of UCC21520 connect to the full-bridge through their own separate gate resistors. The outputs of UCC2895 should not need gate resistors since they are not driving the input gate of the MOSFETs.

    Since the issue still exists, we would like to help solve it. Do you have answers for any of the questions I asked before?

    Regards,
  • 0 in reply to Derek Payne
    Expert 1075 points
    In other word,how the filter between the UCC2895 & UCC21520,
    use TI solution, The G-driver(UCC21520)already break(high side short),after change the ADI solution, everything is ok
  • 0 in reply to Alex Chen9
    Expert 1075 points
    Do you have the UCC21520 with UCC2895 reference design or other UCC series?
  • 0 in reply to Alex Chen9
    TI__Mastermind 28960 points

    Hi Alex,

    TI does not have any reference designs with UCC2895. The UCC3895 has a reference design, but it uses gate drive transformers.

    UCC21520 has many reference designs using TMS320F-series microcontrollers, but I think this is not what you are looking for.

    Can you provide a schematic showing the UCC2895 with related passive components?

    Regards,

  • 0 in reply to Alex Chen9
    TI__Mastermind 28960 points
    Hi Alex,

    Thanks for providing the controller schematic. It looks like their dead time is programmed to more than 500ns, so the UCC21520 DT programming is not responsible for the problems they encountered.

    We can recommend that they change their gate resistors and see if the high side shorts go away. If they still want to try UCC21520, they should try decreasing the turn-off resistors to 5.1 ohms or 3.3 ohms, and increasing their turn-on gate resistor to 10 ohms, to better match the output current of UCC21520 to ADUM4223. If this doesn't work, the last test is to increase both gate resistors to a very large value such as 15 or 20 ohms, to rule out switch node dv/dt beyond the CMTI ratings of UCC21520.

    Regards,