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UCC28722: UCC28722

Rishabh Rishabh
Prodigy 90 points
Part Number: UCC28722
Other Parts Discussed in Thread: PMP10344

Hi there,

I am using UCC28722 for energy meter application with three phase input by using guidelines of SLAU721A.

The components values as per SLAU721A are all same with difference that input instead of single phase its 3 phase bridge rectifier

My issue is that Ic's are getting damaged at normal power Up, I have checked the resistances at various PINs then it shows base drive pin ie PIN 3 of UCC28722 is shorted to ground or

sometimes VDD.

  • 0
    TI__Expert 8210 points
    Rishabh

    Are you referring to this app note www.ti.com/.../slua721a.pdf ?

    It sounds like there is some kind of condition that occurs during your startup that is damaging UCC28722. We recommend that you replace the failed components and attempt to start up your design with a lower input voltage. Carefully measure the voltage on the VDD and input to make sure none of the voltage ratings of the components are exceeded.

    If you are unable to get the design to startup without failing we recommend that you use our PSpice model www.ti.com/.../slum466 to simulate the design to verify that there is no excessive voltage or surge that is causing the failure.

    We also recommend that you verify that the 3 phase rectifier you designed is correct, please use PMP10344 as an example of how to configure a 3 phase bridge rectifier.

    Best Regards,
    Eric
  • 0
    Prodigy 90 points
    Thanks Mr Eric, for reply.

    You are correct I am referring to SLAU721A by Ti for UCC22728.

    Secondly I have verified my 3 phase input that is as per PM10344 the only deviation referred to PM10344 design is that I am not using GND inductor ( L4 ) in -ve of bridge rectifier ie PGND

    also ,C3,R2,R12 not used,

    Is L4 , C3 ( 0.01mfd / 1000 V ) is necessary. also role of resistor across inductor not understood , please elaborate.
    Can I connect any zener at VDD PIN of 30 V to prevent power up damage if yes then plz suggest connection since in SLAU721A pin no. 5 ie GND is not connected to circuit ground.

    I also checked resistances of failed IC that showing short between Base drive ( PIN 3 of UCC22728 ) BJT with VDD or GND or with sometime with PIN no 1.

    and if its power on voltage issue then why BJT drive ( PIN 3 ) should get affected.

    Thanks.
  • 0 in reply to Rishabh Rishabh
    TI__Expert 8210 points
    Rishabh

    L4 and C3 in PMP10344 are part of the input EMI filter.

    I recommend to confirm if the BJT FET is also failed. What could be occurring is that the BJT is failing, which causes a voltage over stress to be applied to UCC28722. If this is the case I recommend that you increase the voltage rating of the BJT or increase the snubber to reduce the voltage overshoot. There could be a voltage spike during startup that is causing a failure.

    Best Regards,
    Eric
  • 0 in reply to Eric Faraci
    Prodigy 90 points

    Thanks Mr. Eric

    The BJT is not failing only UCC28722 is damaging and as Inductor is part of EMI filter I don't think it will help out for input surge if any.

    Secondly I am asking for Zener at VDD to prevent overshoot will it support and connection of PIN5 ie GND to flyback inductor as per SLAU721A is correct?

  • 0 in reply to Rishabh Rishabh
    TI__Expert 8210 points
    Rishabh

    If I understand correctly, you are observing failures with UCC28722 that measure a short from DRV to VDD or DRV to GND when you startup your design and the power BJT does not fail.

    Before applying fixes we recommend to take further measurements to identify what is causing the failure. Based on the failure you described a voltage on one of the UCC28722 pins may be exceeding the abs max or abs min. We recommend you measure the voltage during startup. If any exceeds adding a clamp is a good idea.

    Eric
  • 0 in reply to Eric Faraci
    Prodigy 90 points

    Thanks Mr Eric,

    Failing condition of IC is not always else I would have done it earlier.

    Its happening in 1 attempt out of 200 attempts or sometime not at all in any 1 sample out of 5.

    Its random nature. so I request you to help me out to explore the clamping for sensitive pins u think.

    or some snubber adjustments as you said.

  • 0 in reply to Rishabh Rishabh
    TI__Expert 8210 points

    Rishabh

    If you exceed the abs max rating of UCC28722 the device may not immediately fail.  What abs max means is that once it is exceeded, TI no longer guarantees that the device will operate as specified in the datasheet.  What could happen is that the device could either operate as expected, change operation to a condition that is not desired, or catastrophically fail and not operate anymore.  TI does not specify any operation once the abs max is exceeded.

    You need to measure the voltages that are applied to UCC28722 during startup and operation to see if any abs max limit is exceeded.  If you find them to be exceeded you need to modify your design to prevent this.

    Best Regards,

    Eric