reset capacitor

[tahirmahmood]

How can we select the reset capacitor and the pull up resistor on the reset pin of the MK10DN128VFM5.If I use 10k and 1n on the reset pin then it does not work with all power supplies.But when I change it to 100n it works.How can we calculate the reset capacitor.

[xiangjun_rong]

Hi, Tahir,

Regarding your question, pls refer to section 5.3.2 General switching specifications in data sheet of MK10DN128VFM5, the minimum width of Reset signal is about 100nS.

For a RC circuit(connect a resistor and capacitor serially, connect the another end of resistor to 3.3V, connect another end of capacitor to GND), let's compute the voltage of capacitor(middle node of resistor and capacitor) which is connected to RESET pin.

The capacitor voltage Vc(t)=3.3V*(1-EXP(-t/RC))   //t is a time variable, R is resistor value, C is capacitor value, Vc(t) is the capacitor voltage vs time.

The maximum  value of Low logic is regarded as 0.5V, t is 100nS, R is 10K. We can figure out:

0.5=3.3*(1-EXP(-100*10**(-9)/[10*10**(3)*C]))

we can figure out that the C=60nF. It is okay for you to set the capacitor greater than 60nF.

Hope it can help you

BR

XiangJun Rong