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NPOR in STM32F098

Question asked by Lukasz Przenioslo on Feb 19, 2017
Latest reply on Feb 19, 2017 by Clive One

Hello there,

I am working with STM32F098 mcu, it has NPOR pin. Reading the documentation I understood that I have to externally pull this pin low until a stable VCC will be present. When it is present, I have to leave it high impedance as it has internal pull-up.

For this I use TPS3825:

The TPS3825 helds the #RST line low when #MR is low or until VCC reaches more than 3V. My problem is that in my circuit the NPOR pin acts like an output pulling the #RST line low. After I cut off the NPOR line from the #RST net the mcu started to work. When measuring voltage on NPOR pin then it is 0V.

How does this NPOR pin work really? Did I understand something wrong? I would appreciate all help.