AN8014 Panasonic Semiconductor, AN8014 Datasheet - Page 13

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

Voltage regulators
[1] Function descriptions (continued)
[2] Bootstrap circuit usage notes
9. Bootstrap circuit of output block (continued)
1. Operating voltage range for step-down circuit
2. Value setting of bootstrap capacitor
3. CB pin connection for step-up circuit
Application Notes (continued)
2) N-channel MOSFET (M1) turn-on time: t
3) N-channel MOSFET (M1) turn-off time: t
voltage will be approximately twice as high as V
on. The allowable voltage applied to the CB pin is 35 V. Therefore the operating supply voltage must be within a
range between 3.6 V and 17 V.
of the n-channel MOSFET when the n-channel MOSFET is turned on. At that time bootstrap capacitor is dis-
charged by n-channel MOSFET gate-drive-current. If the capacitance of the bootstrap capacitor is too low, an
increase in switching loss will result, which will reduce the efficiency.
channel MOSFET. Refer to the following.
the n-channel MOSFET is grounded. Therefore, short-circuit the CB pin (pin 14) and the V
Out pin voltage V
on. Then the M1 source-side voltage rises up to the voltage expressed by the following.
voltage rises according to the M1 source-side voltage due to capacitor coupling. V
following formula.
coupling. Then the M1 will be in the state described in the above 1).
Just like what described previously, if a step-down circuit is in DC-DC converter control, the CB pin (pin 14)
V
V
The bootstrap capacitor raises the CB pin voltage to V
Therefore, the capacitance must be large enough in comparison with the gate input capacitance of the n-
Determine the best value by testing on the printed circuit board for mounting.
If a step-up circuit is in DC-DC converter control, no bootstrap circuit is required because the source side of
Thus, the operating supply voltage range in the step-up circuit method is between 3.6 V and 34 V.
CB
CC
When the PWM comparator output is inverted, the Out pin (pin 13) output changes into a high level. The
Then the voltage between the gate and source of the M1 is obtained from the following.
When the Out pin voltage V
The bootstrap capacitor C
The Out pin voltage turns off after rising to the saturation voltage of the AN8014S's internal transistor Q1.
The M1 source-side voltage drops to V
V
V
V
V
C
2
B
O
GS
S
CB
35 V
V
V
C
V
V
V
2 V
CC
iss
CC
CB
O
S
D1
V
V
V
V
CC
O
V
F
D1
CC
DS(ON)
V
CE
2
rises toward the CB pin voltage.
DS (ON)
(sat)
V
V
V
D1
DS (ON)
D1
V
B
V
V
DS(ON)
is connected to the source side and CB pin of the M1. Therefore, the CB pin
O
F
F
is the same as or higher than the gate threshold voltage V
V
[V]
F
V
35 [V]
17 [V]
F
2
3
F
CC
. The CB pin voltage drops to V
when the n-channel MOSFET as a switching element is turned
CC
or higher due to capacitor coupling to the source side
CC
V
D1
or below due to capacitive
CB
CC
is expressed by the
pin (pin15).
TH
AN8014S
, the M1 turns
13