MMDF5N02Z

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5

Figure 8. Gate−To−Source and Drain−To−Source

Voltage versus Total Charge

Figure 9. Resistive Switching Time

Variation versus Gate Resistance

02

4

1

6

4

1

0

6

5

6

5

3

2

0

Q1

Q2

Q3

810

1

100

10

100

10

3

2

4

12

14

1000

QT

DRAIN−TO−SOURCE DIODE CHARACTERISTICS

The switching characteristics of a MOSFET body diode

are very important in systems using it as a freewheeling or

commutating diode. Of particular interest are the reverse re-

covery characteristics which play a major role in determin-

ing switching losses, radiated noise, EMI and RFI.

System switching losses are largely due to the nature of

the body diode itself. The body diode is a minority carrier de-

the typical reverse recovery wave form of Figure 11. It is this

stored charge that, when cleared from the diode, passes

through a potential and defines an energy loss. Obviously,

repeatedly forcing the diode through reverse recovery fur-

ther increases switching losses. Therefore, one would like a

these losses.

The abruptness of diode reverse recovery effects the

amount of radiated noise, voltage spikes, and current ring-

ing. The mechanisms at work are finite irremovable circuit

parasitic inductances and capacitances acted upon by high

trolled by the device clearing the stored charge. However,

teristic and is usually the culprit that induces current ringing.

as a good indicator of recovery abruptness and thus gives a

comparative estimate of probable noise generated. A ratio of

1 is considered ideal and values less than 0.5 are considered

snappy.

Compared to ON Semiconductor standard cell density

low voltage MOSFETs, high cell density MOSFET diodes

verse recovery characteristic. The softness advantage of the

high cell density diode means they can be forced through re-

verse recovery at a higher di/dt than a standard cell MOS-

FET diode without increasing the current ringing or the

noise generated. In addition, power dissipation incurred

from switching the diode will be less due to the shorter re-

covery time and lower switching losses.

0

0.2

0.4

0

1

2

3

Figure 10. Diode Forward Voltage versus Current

0.6

0.8

4

5

0.5

1.5

2.5

3.5

4.5

0.1

0.3

0.5

0.7