CSD15380F3: N channel vs. P Channel

Sunset

Part Number: CSD15380F3
Other Parts Discussed in Thread: CSD23280F3,

Hello Team,

I'm compering the N and P channel MOS.

On the N channels since they are physically smaller (electron mobility is better than hole mobility) I'm not surprises that Qg and Input capacitance is smaller. Nevertheless if I take the ration between two devices P and N (P: CSD23280F3 and N: CSD15380f3) QgP /QgN = 4.4 while CissP/CissN = 22.3

How can I explain it?

How can you derive the Input capacitance out of Qg, if Qg also include the miller capacitance?

Qg should include also the input capacitance effect, beside the miller one, so I would have expected to have a similar ratio.

Thanks for the clarification.

SunSet

over 5 years ago

0 Chris Bull over 5 years ago

TI__Expert 6815 points

Mauro,

Thanks for posting, great question and in 20years + of dealing with FETs this is the first time I have been asked this.
I spoke with some of our technologists and the explanation they gave me was that this is to do with the test conditions (one has Vgs=4.5V the other Vgs=0V) and the difference in voltage on the gate drives a different behavior between Ciss and Qg.

0 Sunset over 5 years ago in reply to Chris Bull

TI__Genius 13385 points

Hello Chris,

thanks for the info.

This means that Cin is measured with Vgs= 0V so that the gate channel is not made and you really measure Cin only (The MOS is OFF).
For the Qg, you need to open the DS channel and Vgs must be beyond Vth. In this way you can also include the miller capacitance effect between the D and G.
Thus you cannot derive Cin directly from Qg, since it include the Q that goes to the Cdg.

Am I thinking right?

Thanks,

SunSet

0 Chris Bull over 5 years ago in reply to Sunset

TI__Expert 6815 points

Mauro,
Yes it is along those lines.

0 Sunset over 5 years ago in reply to Chris Bull

TI__Genius 13385 points

Thanks for the confirmation.
SunSet

Power management

Power management forum

CSD15380F3: N channel vs. P Channel