an8041s Panasonic Corporation of North America, an8041s Datasheet - Page 13

• Manufacturer Part Number: an8041s
• Description: Liquid Crystal Backlight Control Ic
• Manufacturer: Panasonic Corporation of North America

Voltage Regulators
[3] Function descriptions (continued)
8. Output block, bootstrap circuit
Application Notes (continued)
M1 source-side waveform
1) N-channel MOSFET (M1) off time: t
MOSFET is used as the switching device.
threshold voltage of n-channel MOSFET by increasing the high-level of the Out terminal (pin 13) to a level higher
than V
circuit are shown in figure 6, and the operation waveform in figure 7.
Out terminal waveform
CB terminal waveform
CT
DTC
FB1
FB2
In the case of the step-down type DC-DC converter control, the bootstrap circuit is required if n-channel
The bootstrap circuit is used for keeping the voltage between the gate and the source higher than the gate
The bootstrap circuit operation is described below.
the M1 source side voltage V
(pin 15) through the diode inside the IC (D1). The CB terminal voltage (pin 14) V
equation:
CC
While the M1 is off, energy is being supplied from the schottky barrier diode (SBD) to the choke coil, and
Therefore, the charged voltage of boost C
PWM comparator
when turning on the n-channel MOSFET. The output block including the external circuit and the bootstrap
V
V
V
S
CB
CB
V
V
V
F
D1
V
V
S
: forward voltage of SBD
: forward voltage of D1
F
CC
V
0 V
V
CC
V
CC
D1
V
V
D1
D1
Q1
Q2
V
M1 Off
Turn-on
Figure 7. Bootstrap circuit operation waveform
S
F
is fixed to V
t
1
Figure 6. Output block and bootstrap circuit
D1
1
14
13
F
B
I
I
CB
Out
. The capacitor for boost C
1
2
is given by the following equation:
M1 On
t
2
M1
V
CB
GS
V
V
CB
S
SBD
Turn-off
M1 Off
B
is charged from the V
t
3
CB
is given by the following
V
V
V
V
V
V
CBH
OH
CC
CC
OL
F
AN8041S
V
V
0.7 [V]
OUT
CC
DS(ON)
terminal
[V]
13