NTD3055-094T4 ONSEMI [ON Semiconductor], NTD3055-094T4 Datasheet - Page 4

• Manufacturer Part Number: NTD3055-094T4
• Description: Power MOSFET 12 A, 60 V
• Manufacturer: ONSEMI [ON Semiconductor]

by recognizing that the power MOSFET is charge
controlled. The lengths of various switching intervals (Dt)
are determined by how fast the FET input capacitance can
be charged by current from the generator.
The published capacitance data is difficult to use for
calculating 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
rudimentary analysis of the drive circuit so that
t = Q/I
During the rise and fall time interval when switching a
resistive load, V
known as the plateau voltage, V
times may be approximated by the following:
t
t
where
V
R
and Q
During the turn−on and turn−off delay times, gate current is
not constant. The simplest calculation uses appropriate
values from the capacitance curves in a standard equation for
voltage change in an RC network. The equations are:
t
t
r
f
d(on)
d(off)
G
GG
= Q
= Q
Switching behavior is most easily modeled and predicted
= the gate drive resistance
= the gate drive voltage, which varies from zero to V
= R
2
2
2
= R
G(AV)
x R
x R
and V
G
G
G
G
C
C
/(V
/V
iss
iss
GSP
GSP
GG
In [V
In (V
GS
are read from the gate charge curve.
− V
remains virtually constant at a level
GG
GG
GSP
/(V
/V
)
G(AV)
GSP
GG
)
− V
GATE−TO−SOURCE OR DRAIN−TO−SOURCE VOLTAGE (VOLTS)
SGP
800
600
400
200
) can be made from a
0
GSP
. Therefore, rise and fall
10
C
C
)]
iss
rss
V
DS
5
POWER MOSFET SWITCHING
V
= 0 V
Figure 7. Capacitance Variation
GS
0
V
http://onsemi.com
NTD3055−094
GS
V
DS
GG
= 0 V
5
C
rss
4
10
The capacitance (C
a voltage corresponding to the off−state condition when
calculating t
on−state when calculating t
complicate 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 function of drain current, the mathematical solution is
complex.
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 measure and, consequently, is not specified.
resistance (Figure 9) shows how typical switching
performance is affected by the parasitic circuit elements. If
the parasitics were not present, the slope of the curves would
maintain a value of unity regardless of the switching speed.
The circuit used to obtain the data is constructed to minimize
common inductance in the drain and gate circuit loops and
is believed readily achievable with board mounted
components. Most power electronic loads are inductive; the
data in the figure is taken with a resistive load, which
approximates an optimally snubbed inductive load. Power
MOSFETs may be safely operated into an inductive load;
however, snubbing reduces switching losses.
At high switching speeds, parasitic circuit elements
The resistive switching time variation versus gate
15
T
d(on)
The
J
= 25 C
20
and is read at a voltage corresponding to the
C
C
iss
oss
MOSFET
iss
) is read from the capacitance curve at
25
d(off)
output
.
capacitance
also