MMDF2N02E Motorola, MMDF2N02E Datasheet - Page 4

• Manufacturer Part Number: MMDF2N02E
• Description: DUAL TMOS MOSFET 3.6 AMPERES 25 VOLTS
• Manufacturer: Motorola

by recognizing that the power MOSFET is charge controlled.
The lengths of various switching intervals ( t) are deter-
mined by how fast the FET input capacitance can be charged
by current from the generator.
The published capacitance data is difficult to use for calculat-
ing rise and fall because drain–gate capacitance varies
greatly with applied voltage. Accordingly, gate charge data is
used. In most cases, a satisfactory estimate of average input
current (I G(AV) ) can be made from a rudimentary analysis of
the drive circuit so that
t = Q/I G(AV)
During the rise and fall time interval when switching a resis-
tive load, V GS remains virtually constant at a level known as
the plateau voltage, V SGP . Therefore, rise and fall times may
be approximated by the following:
t r = Q 2 x R G /(V GG – V GSP )
t f = Q 2 x R G /V GSP
where
V GG = the gate drive voltage, which varies from zero to V GG
R G = the gate drive resistance
and Q 2 and V GSP are read from the gate charge curve.
MMDF2N02E
4
Switching behavior is most easily modeled and predicted
1200
1000
100
800
600
400
200
10
1
0
10
1
GATE–TO–SOURCE OR DRAIN–TO–SOURCE VOLTAGE (VOLTS)
C iss
Figure 9. Resistive Switching Time Variation
V DD = 10 V
I D = 2 A
V GS = 10 V
T J = 25 C
C rss
V DS = 0 V
5
V GS
Figure 7. Capacitance Variation
versus Gate Resistance
R G , GATE RESISTANCE (OHMS)
0
V GS = 0 V
V DS
5
10
10
t d(off)
t f
t r
t d(on)
15
POWER MOSFET SWITCHING
T J = 25 C
20
C oss
C rss
C iss
100
25
During the turn–on and turn–off delay times, gate current is
not constant. The simplest calculation uses appropriate val-
ues from the capacitance curves in a standard equation for
voltage change in an RC network. The equations are:
t d(on) = R G C iss In [V GG /(V GG – V GSP )]
t d(off) = R G C iss In (V GG /V GSP )
The capacitance (C iss ) is read from the capacitance curve at
a voltage corresponding to the off–state condition when cal-
culating t d(on) and is read at a voltage corresponding to the
on–state when calculating t d(off) .
plicate the analysis. The inductance of the MOSFET source
lead, inside the package and in the circuit wiring which is
common to both the drain and gate current paths, produces a
voltage at the source which reduces the gate drive current.
The voltage is determined by Ldi/dt, but since di/dt is a func-
tion of drain current, the mathematical solution is complex.
The MOSFET output capacitance also complicates the
mathematics. And finally, MOSFETs have finite internal gate
resistance which effectively adds to the resistance of the
driving source, but the internal resistance is difficult to mea-
sure and, consequently, is not specified.
12
9
6
3
0
At high switching speeds, parasitic circuit elements com-
7
6
5
4
3
2
1
0
0.5
Motorola TMOS Power MOSFET Transistor Device Data
0
Q1
Drain–to–Source Voltage versus Total Charge
T J = 25 C
VGS = 0 V
Q3
V DS
0.6
2
V SD , SOURCE–TO–DRAIN VOLTAGE (VOLTS)
Figure 10. Diode Forward Voltage
Figure 8. Gate–to–Source and
Q2
Q g , TOTAL GATE CHARGE (nC)
0.7
4
versus Current
QT
0.8
6
0.9
8
V GS
I D = 2.3 A
T J = 25 C
10
1
12
1.1
16
12
4
8
0