# Turn on and turn off timing in Mosfet

#### Kusagi

Joined Jul 9, 2021
3
How CGSO and CGDO affect to turn on and turn off timing in Mosfet?
and how can i get CGSO and CGDO value from datasheet?

#### LowQCab

Joined Nov 6, 2012
3,454
They need to be "Modeled" in a Computer Program to display their interactions.
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#### Ian0

Joined Aug 7, 2020
8,406
Cgso has to be charged by the gate driver.
Cgdo suffers from the Miller effect, so appears as though it is larger than it is by a factor equal to the voltage gain of the stage.
As the voltage gain of a power MOSFET stage is not so easy to quantify, it is often easier to think in terms of gate Charge instead of gate Capacitance. Switching times are approximately equal to gate charge divided by gate current.
But, as @LowQCab says, let SPICE do the work!

#### Kusagi

Joined Jul 9, 2021
3
They need to be "Modeled" in a Computer Program to display their interactions.
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View attachment 243012
That means we can't calculate CGDO and CGSO parameters.
But I see in the picture which you attached above have equation:
Ciss = CGS + CGD
Coss = CDS + CGD
So could I calculate CGS0= Ciss-Crss , and CGDO = Crss ?

#### LowQCab

Joined Nov 6, 2012
3,454
I have never seen the terms CGD and CGS with an "O" added to the end,
What does the "O" represent ?

"" So could I calculate CGS0= Ciss-Crss...... ""
CGS, CDG, and CDS are Specific-Measurements.
Ciss, Crss, and Coss, are "Derived-Values".
Study the picture provided, most of the important formulas are there.
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#### Kusagi

Joined Jul 9, 2021
3
Cgso has to be charged by the gate driver.
Cgdo suffers from the Miller effect, so appears as though it is larger than it is by a factor equal to the voltage gain of the stage.
As the voltage gain of a power MOSFET stage is not so easy to quantify, it is often easier to think in terms of gate Charge instead of gate Capacitance. Switching times are approximately equal to gate charge divided by gate current.
But, as @LowQCab says, let SPICE do the work!
I have never seen the terms CGD and CGS with an "O" added to the end,
What does the "O" represent ?

"" So could I calculate CGS0= Ciss-Crss...... ""
CGS, CDG, and CDS are Specific-Measurements.
Ciss, Crss, and Coss, are "Derived-Values".
Study the picture provided, most of the important formulas are there.
.
.
.
I found that paramete in PSPICE MODEL

#### Attachments

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#### LowQCab

Joined Nov 6, 2012
3,454
The Program is asking for You to look at the Data-Sheet for
the CGS, CDG, and CDS values,
for the particular MOSFET that You would like to use as a Model in your new Circuit.
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