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STM32F103 NRST PIN CAPACITOR VALUE?

cbyun.1
Associate

There was a phenomenon that booting was not possible during the low temperature test.

The NRST external switch is equipped with a 100pF capacitor.

The datasheet recommends installing 100nF.

However, I don't think it will be a problem because the MIN value is more than 300ns.

If you install 100nF, it will boot normally.

Why can't I mount 100pF?

RC= 8K (40K (internal pull-up resistor) // 10K (external pull-up resistor)) * 100pF

Over 300ns.

2 REPLIES 2
Uwe Bonnes
Principal III

100 pF will release NRST very fast, Probably some internal "TEMPORIZATION" timing is not meet.

ONadr.1
Senior III

The capacitor should also block superimposed interference and prevent unwanted resets. That's why there is a recommended capacitance of 100nF.