Hi !

I had contributed a discussion already.

(ADuM3223/4223)To calculate the power consumtion.

And I have onequestion again.

At the data sheet P17 , it is caｌculate the R_DSON_P and R_DSON_N.

Why is it calculating both?

I think in the device , it won't happen P-MOS=>ON and N-MOS=>ON,

so, I think that the calculation of either is enough.

I would really appreciate if you don't mind to teach me about this.

Best regards

Kawa.

Hello Kawa,

The reason both Rdson_N and Rdson_P are used is because there are two times power is dissipated in the charging and discharging of a capacitor, which is on way of modelling a device gate.

The energy stored in a capacitor is: 1/2 * C * V^2 where C is the equivalent gate capacitance, and V is the voltage of the capacitor. We can also use Q=CV to get 1/2 * Q * V, where Q is the gate charge. The counter intuitive thing is that to charge a capacitor, we must also dissipate that much energy. Also, to discharge that capacitor, we must once again see the power dissipation, so the total power in the system consists of both a charging and a discharging in each cycle.

For the charging path, the gate driver PMOS device is on, so we must look at the ratio of the internal Rdson_P compared to the charging path external series resistance. For the discharging, the ratio between the Rdson_N and the discharging external series resistance is used.

RSchnell