FAN3111C Fairchild Semiconductor, FAN3111C Datasheet - Page 14

• Manufacturer Part Number: FAN3111C
• Description: The FAN3111 1A gate driver is designed to drive an N-channel enhancement-mode MOSFET in low-side switching applications
• Manufacturer: Fairchild Semiconductor

© 2008 Fairchild Semiconductor Corporation
FAN3111 • Rev. 1.0.2
Truth Table of Logic Operation
The FAN3111 truth table indicates the operational states
using the dual-input configuration. In a non-inverting
driver configuration, the IN- pin should be a logic low
signal. If the IN- pin is connected to logic high, a disable
function is realized, and the driver output remains low
regardless of the state of the IN+ pin.
Table 1. FAN3111 Truth Table
In the non-inverting driver configuration in Figure 41, the
IN- pin is tied to ground and the input signal (PWM) is
applied to the IN+ pin. The IN- pin can be connected to
logic high to disable the driver and the output remains
low, regardless of the state of the IN+ pin.
In the inverting driver application shown in Figure 42, the
IN+ pin is tied high. Pulling the IN+ pin to GND forces the
output low, regardless of the state of the IN- pin.
Figure 42.
PWM
PWM
Figure 41.
IN+
0
0
1
1
Dual-Input Driver Enabled, Inverting
IN+
IN-
Dual-Input Driver Enabled, Non-
Inverting Configuration
IN+
IN-
Configuration
FAN3111
FAN3111
IN-
0
1
0
1
VDD
VDD
GND
GND
OUT
OUT
OUT
0
0
1
0
14
Thermal Guidelines
Gate drivers used to switch MOSFETs and IGBTs at
high frequencies can dissipate significant amounts of
power. It is important to determine the driver power
dissipation and the resulting junction temperature in the
application to ensure that the part is operating within
acceptable temperature limits.
The total power dissipation in a gate driver is the sum of
three components; P
Gate Driving Loss: The most significant power loss
results from supplying gate current (charge per unit
time) to switch the load MOSFET on and off at the
switching frequency. The power dissipation that results
from driving a MOSFET at a specified gate-source
voltage, V
frequency, f
Dynamic Pre-drive / Shoot-through Current: A power loss
resulting from internal current consumption under
dynamic operating conditions, including pin pull-up / pull-
down resistors, can be obtained using the graphs in
Figure 11 and Figure 12 in Typical Performance
Characteristics to determine the current I
from V
Once the power dissipated in the driver is determined,
the driver junction temperature rise with respect to the
device lead can be evaluated using thermal equation:
where:
T
θ
T
The power dissipated in a gate-drive circuit is
independent of the drive-circuit resistance and is split
proportionately among the resistances present in the
driver, any discrete series resistor present, and the gate
resistance internal to the power switching MOSFET.
Power dissipated in the driver may be estimated using
the following equation:
where:
P
R
I
R
the driver output and the gate of the MOSFET; and
R
and source connections.
P
OUT
P
P
P
T
JL
J
L
PKG
OUT,DRIVER
EXT
GATE,FET
PKG
total
GATE
DYNAMIC
J
= driver junction temperature;
= lead temperature of device in application.
= thermal resistance from junction to lead; and

vs. V
P
= power dissipated in the driver package;
= external series resistance connected between


DD
TOTAL

P
P
gate
TOTAL
Q
under actual operating conditions:
OUT
= resistance internal to the load MOSFET gate
G
GS
SW

= estimated driver impedance derived from


I
waveforms;
, with gate charge, Q

DYNAMIC
, is determined by:
JL
P




V
Dynamic
R
GS

OUT,
T

C
GATE
f
sw
DRIVER

V
, P
DD
R
QUIESCENT
OUT,

R
EXT
Driver
, and P

R
G
GATE,
, at switching
DYNAMIC
DYNAMIC
www.fairchildsemi.com
FET




drawn
:
(1)
(2)
(3)
(4)
(5)