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LM5574 Vin Max rating

Ross Parlour
Intellectual 1450 points

Hi Team,

Could you help answer the questions below I have from my customer please?

"My query is regarding the maximum input voltage... The absolute maximum voltage is specified in your datasheet as 76V. The maximum input voltage we can expect to experience is 66V which is easily in range. However here at Thales we have our own derating policy which means our own maximum allowable input voltage is 60.8V so we are in violation of our policy.

I am assuming you have your own safety margins which you abide by when specifying the absolute maximum ratings for device parameters.

Could you provide details of these safety margins?

Could you also inform me of what voltage the device has been tested up to and still worked?

Could you also specify what it is about the device which fails. Is it a complete electrical breakdown or is it thermal related? 

Is the damage instantaneous at power up or will it fail after exposure for a duration?"

Many thanks in advance for your support on this.

Best regards,

Ross

  • 0
    TI__Genius 11085 points

    Hello Ross,

    The specified abs max voltage in the datasheet comes from process specification and reliability test. All of the reliability test and production test are proformed at this voltage. Yes there's margin, but operating above abs max voltage is not recommended and will impact the life span of the IC. I'm sure we've tested Vin at higher voltage to 'break the part' on the bench. But bench test is only on a small sample set. The result cannot be applied directly to production. There will be part to part variation on the actural break down voltage. The junction temperature also matters.

    How the device fails when supply voltage is above abs max depends on the amount of over voltage and slew rate, etc. If there's only a relatively small over voltage, you might only see issue over a long peried of time. But if the voltage spike is high with fast slew rate, it could damage the IC instantly. The damage could be the ESD cell of the VIN pin, the power FET got damaged with higher leakage current, or IC fails/cannot work anymore.

    Again, it is not recommended to operate with supply voltage higher than abs max for reliebility concerns.

    -Yang