What is the maximum allowed voltage on a I/O-pin operating in wired-or (open drain) mode on the MC9S12XEP100?

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What is the maximum allowed voltage on a I/O-pin operating in wired-or (open drain) mode on the MC9S12XEP100?

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utwig
Contributor III

Hi,

I would like to control a +12 V line with a P-type MOSFET using the MC9S12XEP100 MCU. I wonder how high voltages it is possible to have on pins configured to operate in wired-or (open drain) mode? My idea is to have the MOSFET gate pulled to +12 V with a pull-up resistor while the wired-or pin is floating and pulled down to GND when I want to turn on the MOSFET. The +12 V line is further regulated down to a very smooth +5 V voltage after the MOSFET, so I have to use a high side switch to avoid voltage losses on this +5 V regulated bus.

 

I failed to find this information in the MC9S12XEP100 data sheet.

 

Cheers,

Timo

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RadekS
NXP Employee
NXP Employee

Hi Timo,

You are right, this idea unfortunately do not work. Wired-or output at MCU is not real open collector solution. We use standard GPIO output driver and just higher transistor is not driven.

Every GPIO pin is protected by ESD diodes to power supply rail. So, voltage at pin will be VDDX+VDESD ( typically 5V+0.7V). Maximum allowed voltage on pin is not affected by wire-or mode and it is specified as VDD35 + 0.3V.

When attached voltage is higher, injection current will flow through internal ESD diode to power supply rail. Maximum allowed injection current is 2.5mA.

More details about GPIO pins could be found in our application note AN2434 Input-Output Pin Drivers on HCS12 Family MCUs

http://www.nxp.com/files/microcontrollers/doc/app_note/AN2434.pdf

Note: this application note was created for older S12 MCU families (built on 250nm technology), therefore some details do not fit to S12XE. However most of information are still valid.


I hope it helps you.

Have a great day,
RadekS

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RadekS
NXP Employee
NXP Employee

Hi Timo,

You are right, this idea unfortunately do not work. Wired-or output at MCU is not real open collector solution. We use standard GPIO output driver and just higher transistor is not driven.

Every GPIO pin is protected by ESD diodes to power supply rail. So, voltage at pin will be VDDX+VDESD ( typically 5V+0.7V). Maximum allowed voltage on pin is not affected by wire-or mode and it is specified as VDD35 + 0.3V.

When attached voltage is higher, injection current will flow through internal ESD diode to power supply rail. Maximum allowed injection current is 2.5mA.

More details about GPIO pins could be found in our application note AN2434 Input-Output Pin Drivers on HCS12 Family MCUs

http://www.nxp.com/files/microcontrollers/doc/app_note/AN2434.pdf

Note: this application note was created for older S12 MCU families (built on 250nm technology), therefore some details do not fit to S12XE. However most of information are still valid.


I hope it helps you.

Have a great day,
RadekS

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

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