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# UCC2813-1: About Vcc of Absolute Maximum Ratings

Part Number: UCC2813-1

Hello,

Regarding to Absolute Maximum Ratings on UCC2813-1, my customer is asking some question.

They are understanding that even if Vcc exceeds 12V(Absolute Maximum Ratings), it is no problem when Icc does not exceed 10mA.

Because this device has internal ZD(13.5V).

(They understand that internal ZD current is 10mA.)

So they will use upto 16V as Vcc.

Their schematics(around Vcc) is following.

(Question)

(1) Their understanding is correct?

According to the note (3) in Absolute Maximum Ratings section, I believe that it should keep ratings(12V) any case.

(2) Does UCC2813-1 have internal ZD(13.5V).?

If so, what purpose is internal ZD used for?

Regards,

Tao2199

• Hello Tao,

Your customer cannot apply 16V to VCC

Note 3 in the data sheet explains that :

"In normal operation VCC is powered through a current limiting resistor. The resistor must be sized so that the VCC voltage under

operating conditions is below 12 V but above the turnoff threshold. Absolute maximum of 12 V applies when VCC is driven from a low

impedance source such that ICC does not exceed 30 mA"

VCC can be connected to a voltage greater than 12V through a resistor but the resistor should have a voltage drop such that the voltage at the VCC pin is never greater than 12V. So in your schematic R66 to R71 limit the high voltage DC and VCC is less than 12V during startup. But during normal operation VCC comes from somewhere not shown in the schematic and this voltage is required to be less than 12V

The 13.5V zener shown in the block schematic is for transient type protection and cannot be used to limit the value of VCC

Regards

John