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Pulling up a GPIO to 9v

0donrobison
Associate
Posted on April 01, 2017 at 04:33

I have the STM32F4 discovery board.  I want to use the GPIO to drive the gate of a power MOSFET up to 9V.  Everything works well with push/pull output, then I configured the pin for open drain output, and add the resistors and 9V supply.  I pulled the pin up to 9volts with 10kohm and down to ground with 1Mohm.  The output looks fine when it's low, but when I try to toggle it high it just goes up like 0.1v but is still low.

I was looking at the output more, and I noticed there are protection diodes on the I/O pins.  I think this might be my problem.  Is it even possible to pull up the output pin above 3v when configured open drain?  What is the max limit? 

2 REPLIES 2
S.Ma
Principal
Posted on April 01, 2017 at 07:53

Some pins are 5V tolerant (usually pins without analog function in it), which for example can implement a 5V I2C bus with open drain pull ups. Exposing a pin beyond its guaranteed limit voids normal operation. There is an absolute maximum rating table in datasheet of any IC part which tells that in those conditions, parts may survive up to 1000 hours....

Protection diods on GPIOs are not supposed to be used beyond absorbing ESD shocks. Overall a transistor uses a gate oxide which thickness yields a breakdown voltage. As process makes smaller transistors, gate thickness shrinks vertically too, or they take more real estate on the chip area.... so in short: If you'd like to control a high voltage stage, put between a discrete transistor.

David Littell
Senior III
Posted on April 01, 2017 at 15:06

I think you probably need a bipolar in front of the power MOSFET.