#### raman00084

##### Full Member level 6

RISE TIME IS THE FASTEST INCOMING EDGE

To calculate the value of R and C, use the following steps:

Find the fastest edge of the incoming signal – or determine the fastest frequency of the incoming signal and assume an edge speed of 1/100th of the input period (a 1 kHz input frequency has an edge of 10 µs).

Select ‘R’. Usually this can be selected to a common value already in the system, such as 1 kΩ.

Use the equation in Figure 9 to determine the value of ‘C’.

In some cases, the input signal is a very slow moving signal (button press, switch closure, etc.), so the value of ‘C’ can be then changed to match a common value on the board, as long as the order of magnitude is maintained.

As shown in Figure 8, the values for R and C are 1 kΩ and 0.01 µF (assumed a maximum input frequency of 1 kHz). Figure 10 shows how this circuit works with the input switch circuit. Note how the overshoot edges are now gone compared to Figure 7. This is the effect of the capacitor.

KINDLY TEL ME WHAT IS RAISE TIME OF 50 KHZ FREQUENCY AND HOW TO CALCULATE IT

ALSO THE VALUE OF R AND C

THE ARTICLE IS IN THE LINK :http://www.digikey.com/en/articles/techzone/2012/apr/protecting-inputs-in-digital-electronics

REGARDS

KALYAN