MMDF2C02E Motorola, MMDF2C02E Datasheet - Page 6

• Manufacturer Part Number: MMDF2C02E
• Description: COMPLEMENTARY DUAL TMOS POWER FET 2.5 AMPERES 25 VOLTS
• Manufacturer: Motorola

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 determining
switching losses, radiated noise, EMI and RFI.
the body diode itself. The body diode is a minority carrier de-
vice, therefore it has a finite reverse recovery time, t rr , due to
the storage of minority carrier charge, Q RR , as shown in 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 further
increases switching losses. Therefore, one would like a
diode with short t rr and low Q RR specifications to minimize
these losses.
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
MMDF2C02E
6
The switching characteristics of a MOSFET body diode
System switching losses are largely due to the nature of
The abruptness of diode reverse recovery effects the
DRAIN–TO–SOURCE DIODE CHARACTERISTICS
di/dt = 300 A/ s
Figure 7. Reverse Recovery Time (t rr )
t, TIME
di/dts. The diode’s negative di/dt during t a is directly con-
trolled by the device clearing the stored charge. However,
the positive di/dt during t b is an uncontrollable diode charac-
teristic and is usually the culprit that induces current ringing.
Therefore, when comparing diodes, the ratio of t b /t a 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.
MOSFETs, high cell density MOSFET diodes are faster
(shorter t rr ), have less stored charge and a softer reverse re-
covery 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 gen-
erated. In addition, power dissipation incurred from switching
the diode will be less due to the shorter recovery time and
lower switching losses.
Standard Cell Density
High Cell Density
Compared to Motorola standard cell density low voltage
Motorola TMOS Power MOSFET Transistor Device Data
t a
t rr
t rr
t b