AN8014 Panasonic Semiconductor, AN8014 Datasheet - Page 12

• Manufacturer Part Number: AN8014
• Description: Step-down/ step-up/ or inverting DC-DC converter control IC
• Manufacturer: Panasonic Semiconductor

AN8014S
12
[1] Function descriptions (continued)
9. Bootstrap circuit of output block
Application Notes (continued)
1) N-channel MOSFET (M1) off time: t
a bootstrap circuit is required.
level of the Out pin (pin 13) than V
bootstrap circuit including the external circuit. Figure 8 shows the operating waveform of the bootstrap circuit.
M1 source side waveform
If the n-channel MOSFET is used as a switching device for DC-DC converter control of step down method,
Bootstrap circuit ensures that the gate-source voltage is gate threshold voltage or higher by going up the high
The following describes the operation of the bootstrap circuit.
and the source-side voltage V
pin (pin 15) through the AN8014S's internal diode D1.
While the M1 is turned off, the choke coil is provided with energy from the schottky barrier diode (SBD)
The voltage V
Therefore, the charged voltage of bootstrap capacitor C
Out pin waveform
CB pin waveform
V
V
V
DTC
S
CB
CB
CT
FB
V
V
PWM comparator
F
D1
V
V
V
: Forward voltage of SBD
: Forward voltage of D1
F
CC
S
V
V
CB
0 V
V
CC
CC
D1
on the CB pin (pin 14) is expressed by the following.
V
D1
Turns off
Figure 8. Bootstrap circuit operating waveform
S
M1 Off
Figure 7. Bootstrap circuit of output block
of the M1 is fixed to V
V
V
CC
t
1
V
F
D1
CC
voltage when n-channel MOSFET turns on. Figure 7 shows the output of
15
Q1
Q2
1
D1
14
13
Out
I
CB
I
1
2
M1 On
t
2
F
. The bootstrap capacitor C
B
M1
is expressed by the following.
V
GS
C
B
V
V
S
CB
Turns off
M1 Off
SBD
t
3
Voltage regulators
B
is charged from the V
V
V
V
V
V
V
CBH
CC
CC
OL
OH
F
V
0.7 [V]
DS(ON)
V-Out
[V]
CC