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UCC21520: Reason for UCC21520A Device failure showing Impedance between INB and GND,VCCI and GND as 52 ohms

selvam perumal
Intellectual 515 points
Part Number: UCC21520

Hi,

I am using UCC21520A as half bridge gate driver IC with 15V Vcc supply.VDDA supply =6.5V(Bootstrap supply  regulated by LDO TPS7a1601).

Device gets failed twice.Both the time,The impedance between INB and GND,VCCI and GND shows 52 ohms.

What can be the reason for the device failure.I ave attached the schematics for your reference.

With regards,

P.Selvam.

Driver section.pdf

  • 0
    TI__Guru**** 189399 points
    Hi,

    Sorry you are having difficulties with our device. I looked at your schematic , and I didn't see any decoupling on VCCx to VSSx. This is discussed in the d/s in section 10 Power Supply Recommendations. This could likely explain the failures that you are seeing.
  • 0
    TI__Mastermind 28960 points

    Hello Selvam,

    Typically a reduction in impedance between INB/GND or VCCI/GND indicates that an overvoltage transient condition has caused damage to the primary side supply. This could happen in several ways:

    • The 15V supply sees a transient >20V, the absolute maximum of the VCCI pin
    • The inputs see a transient due to line inductance or other layout-related parasitics which damages the ESD cells
    • The driving input supply voltage increases beyond the VCCI input supply voltage, causing high current damage to the ESD structure on the input/supply pins (I have seen this happen frequently during bench testing when supply pins are clamped to 0V but driving input sources are still enabled)

    To correct for these issues, I have the following recommendations:

    • Ensure that the 15V supply is well regulated and free of transients beyond the absolute maximum ratings
    • Add a series resistor before C24 to limit the total short circuit current drawn by this pin and to filter any remaining transients (ICCI should be <5mA, so this resistor can be tens or even hundreds of ohms without affecting VCCI operation; however, be careful to ensure that INA and INB voltage does not exceed VCCI beyond absolute maximum ratings)
    • Ensure that INA and INB driving signals are reduced to 0V before removing the VCCI supply
    • Ensure that INA and INB signals are clean and free of excessive ringing, including both overshoot and undershoot. The datasheet application section for UCC21520A suggests the use of small value filter capacitors to help filter transients and damp excessive ringing, with a filter corner frequency set approximately one order of magnitude beyond the highest application frequency required.

    Regards,