NTMD2C02R2

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7

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

recovery characteristics which play a major role in

determining 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

the typical reverse recovery wave form of Figure 24. 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

further increases switching losses. Therefore, one would

minimize these losses.

The abruptness of diode reverse recovery effects the

amount of radiated noise, voltage spikes, and current

ringing. The mechanisms at work are finite irremovable

circuit parasitic inductances and capacitances acted upon by

controlled by the device clearing the stored charge.

diode characteristic and is usually the culprit that induces

current ringing. Therefore, when comparing diodes, the

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

reverse recovery characteristic. The softness advantage of

the high cell density diode means they can be forced through

reverse recovery at a higher di/dt than a standard cell

MOSFET 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

recovery time and lower switching losses.

N−Channel

P−Channel

Figure 19. Diode Forward Voltage versus Current

Figure 20. Diode Forward Voltage versus Current

1

0

0.9

0.8

0.7

0.6

0.5

0.4

0.4

0.8

1.2

1.6

2

0

0.2

0.4

0.6

0

1

2

5

3

1.2

4

0.8

1.0