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UCC28063: To interpret the UCC28063 VCC/GDA&B max current rating

Eric Lai
Expert 4940 points
Part Number: UCC28063

Hi Expert,

The customer's quality team is followed the datasheet's absolute maximum current ratings to judge the UCC28063 design. 

Questions:

1) The DS is defined the ±25mA for Continuous gate current.But they can get the 50mA ~ 60mA RMS from the UCC28063 GDA&B pin directly.

2)The DS is defined the 20mA for Continuous input current of VCC pin.But they can see the VCC pin RMS current over the 20mA. 

And the customer mentioned they can be measured from their legacy UCC28063 designs.

Pls advice us how to interpret the max current rating of UCC28063 VCC/GDA&B. 

Best regards,

Eric Lai

  

Field Application Engineer

Texas Instruments Taiwan Limited

O: +886-2-2175-2582

M: +886-909-262-582

E-Mail:Eric.Lai@ti.com     

  • 0
    TI__Mastermind 26840 points

    Hello Eric,

    Thank you for your interest in the UCC28063 Interleaving-TM PFC controller.

    These continuous maximum ratings are Average current, not RMS.  I can understand why there may be confusion. 
    The typical gate drive current is not continuous at all, but a series of tall narrow peaks, as seen in Figures 13 and 14 of the datasheet.   Using a rough triangular approximation of the waveshape and 100kHz (10us) repetition rate, I calculate that the rising gate drive RMS current = ~58mArms and the falling current = ~89mArms, however, their average currents are only 5mA and 6mA respectively.  The high peak to pulse-width aspect ratio makes the rms value much higher than the average. 

    Since the rising gate charge necessarily comes from the VCC rail, Ivcc will also have such high but narrow peak current content.  The absolute maximum ratings are based on continuous dc average current, not on the rms values of these peak currents. 

    I hope this addresses your customer's concerns satisfactorily.

    Regards,
    Ulrich