MPC5643L Injection current under non supplied condition

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MPC5643L Injection current under non supplied condition

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rakeshshetty
Contributor II

Dear all,

Currently, in one of our project i am using MPC5643L Leopard Microcontroller. Usually in microcontroller datasheet will specify the value of injection current as 1mA for the supplied condition i.e. VDD=3.0V to 3.6V,considering diode voltage drop of 0.3V. But I have a situation in my application where I am applying signal to the input pin of  the microcontroller before the 3.3V supplied, and the time duration is around 50ms ( Input voltage:12V given to voltage divider 51K and 5.11K. PFA) .

I consider this as non-supplied condition, and injection current limit under this condition is not mentioned in datasheet.

I have the following questions which I need some information's.

a) What value of injection current should be considered under this condition? Is there any timelimit?

b) Injection Current is also specified for overload condition i.e 10mA. Whether this overload condition is applicable for transient signals under supplied condition or non supplied condition?

c) Is there any another design consideration, since applying input signals under non supplied condition will result in increase of supply voltage and unintended operation of the MCU has to be prohibited.

P.S: This Current configuration can not be avoided in our application

Any help is appreciated

regards

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rakeshshetty
Contributor II

Hello Peter,

Thank you for your response.

Yes, I have already gone through this application note. Do you have any additional information related to my question a) and b).

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petervlna
NXP Employee
NXP Employee

Hello,

When the power supplies are off, injection current may cause the power supply to rise above 0 volts. In this case, it is
important to ensure that the voltage is not too large and that the MCU is kept in reset when the voltage is lower than the
minimum operating voltage of the device.

For more details refer to:

http://cache.nxp.com/assets/documents/data/en/application-notes/AN4731.pdf?fsrch=1&sr=1&pageNum=1 

Peter