Principle of RC reset circuit and calculation of Reset time

Principle of RC reset circuit and calculation of Reset time

The low-level effective reset circuit is as follows:

 

This reset circuit is designed for low-level effective reset, where the diode is capable of quickly releasing the voltage at both ends of the capacitor when the power is down to prepare for the next power-on reset.

Assume that the initial voltage at both ends of the capacitor is U0 (usually set to 0 V), and the voltage at both ends of the capacitor is ut. 3.3v voltage is set to VCC.

The relationship between current I and voltage at both ends of the capacitor: I = C * DUT/dt

We can get: I * dt = C * du t

Points on both sides can be obtained: I * t = random (0-1) C * DUT; that is, I * t = C * UT? C * U0 (U0 = 0 V ),

The formula for VCC = Ur + Ut is as follows: VCC = R1 * (C * ut/t) + Ut

Assuming that the reset is completed when the capacitor is charged to 0.9 * VCC, t = 9 * RC can be obtained, and T is the reset time required.

Generally, the reset time of the chip is given. In R and C, you can determine a value and then find another value.

 
 
 

 

Let's take a look at the calculation process of the reset time of the RC Circuit when a high-level effective reset is performed: The corresponding schematic diagram is as follows:

 

 

Assume that the initial voltage at both ends of the capacitor is U0 (usually set to 0 V), and the voltage at both ends of the capacitor is ut.

The charging current of the capacitor is:

Similarly, the current value of the resistance passing through T is I = C1 * the voltage at both ends of the VCC/T resistance can be determined: UR = R1 * (C1 * ut/T)

So again: VCC = Ur + uc1

 

 

The capacitor is charged as ut at t time. If ur ≥0.9vcc and the high-level reset is effective, ut = 0.1vcc can exist,

Therefore, it can be: 0.9vcc = R1 * (C1*0.1 * VCC/T), so we can get: t = (1/9) * R1 * C1.

T is the required reset time. The resistance and capacitance in the schematic diagram determine a value and you can find another value.

Principle of RC reset circuit and calculation of Reset time