MMDF7N02Z datasheet(6/12 Pages) ONSEMI

6 / 12 page

MMDF7N02Z

http://onsemi.com

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

Voltage versus Total Charge

RG, GATE RESISTANCE (OHMS)

1.0

100

VDD = 25 V

ID = 1.0 A

TJ = 25_C

td(off)

td(on)

Figure 9. Resistive Switching Time

Variation versus Gate Resistance

6.0

3.0

2.0

1.0

QG, TOTAL GATE CHARGE (nC)

5.0

3.0

5.0

TJ = 25_C

VDS

VGS

1000

9.0

4.0

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

device, therefore it has a finite reverse recovery time, trr, due

to the storage of minority carrier charge, QRR, as shown in

the typical reverse recovery wave form of Figure 15. 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

like a diode with short trr and low QRR specifications to

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

high di/dts. The diode’s negative di/dt during ta is directly

controlled by the device clearing the stored charge.

However, the positive di/dt during tb is an uncontrollable

diode characteristic and is usually the culprit that induces

current ringing. Therefore, when comparing diodes, the

ratio of tb/ta serves 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

are faster (shorter trr), have less stored charge and a softer

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.

0.4

2.0

1.0

5.0

3.0

0.5

0.6

0.7

0.8

4.0

VSD, SOURCE−TO−DRAIN VOLTAGE (VOLTS)

Figure 10. Diode Forward Voltage versus Current

TJ = 25_C

6.0

7.0

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