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ISO6763: Unknown Failure Caused Internal Short Between Ground and VCC Pins

coco walsh
Prodigy 40 points
Part Number: ISO6763

My team included this digital isolator in a recent design and experienced a surprising failure mode. We noticed that an mcu communicating through the digital isolator began to smoke and ultimately was destroyed. We detected that a short existed between VCC and ground on the mcu side of the digital isolator which most likely is what fried the mcu. We removed the digital isolator from the pcb and there was no longer a short on the pcb. However, when probing the VCC2 (pin 16) and GND2 (pin 9) pins on the disconnected isolator, we discovered that there was continuity between them.

This suggested to us that the chip failed in a way which caused a short circuit between power and ground. We are unsure of why the chip failed, but the implications of this type of failure seems severe. Is this a common failure mode for this part?

  • 0
    TI__Mastermind 29595 points

    Hello Coco,

    Thanks for reaching out and sorry to hear about your issue. I am very surprised that this caused the MCU to melt and not the isolator itself. 

    A VCC to GND short can happen if damage to one of the VCC pin occurs. This can happen if the VCCx Absolute Maximum conditions are violated. If the power rail in your application is expecting variance or high voltage transients, then design considerations need to be made to prevent 6.1 Absolute Maximum Ratings values from being exceeded. Please take a look at (+) ISO1042: Vcc1 Damage short to ground - Isolation forum - Isolation - TI E2E support forums which recommends some solutions. 

    If exceeding the voltage limit is truly a risk in your application, then please see 6.8 Safety Limiting Values. Following these current recommendations will prevent further damage to the device by limiting excessive current draw from a VCCx to GNDx short should a side of the isolator fail from over voltage.

    Understanding failure modes in isolators (Rev. A) (ti.com) may be a helpful document to look at as well for more information. 

    Best,
    Andrew