AN4150

Synchronous buck converter testing demonstration board

Doc ID 023526 Rev 1

9/20

To overcome these difficulties, in the real board, the Power MOSFET gate current

measurement is made by using a “Rogowski coil” current probe (CWT ultra mini), properly

connected to the Power MOSFET gate pin. The features of this device are interesting,

because it is flexible and open-ended and can be wrapped around a conductor without

disturbing it. Moreover, it is able to respond correctly to fast-changing currents and it is

highly linear even at very high current levels.

In Figure 6, the Rogowski coil probe end placing on a Power MOSFET DPAK gate pin is

shown.

2.1

Power MOSFET selection for comparative tests

The aim of this document is to evaluate and explain the MOSFET technology gate current

relationship; the analysis starts by choosing two different low-side devices, with the same

die size, to be tested on the board:

a)

Device A - “planar” technology

b)

Device B - “trench” technology

Power MOSFET dynamic parameters (intrinsic capacitances and resistances) are reported:

Figure 7 gives the cross sections of the two above mentioned devices.

Figure 6.

AM14943v1

Table 1.

Power MOSFET electrical parameters

Device

(nC)

(nC)

(nC)

Ciss @ 25 V

Crss @ 25 V

Coss @ 25 V

(

Ω)

A

14

6.8

4.7

1850

58

380

1.2

B

20

8.2

7.5

2200

280

400

1.1