s-8333aaca-t8t1g Seiko Instruments Inc., s-8333aaca-t8t1g Datasheet - Page 15

• Manufacturer Part Number: s-8333aaca-t8t1g
• Description: Step-up, For Lcd Bias Supply, 1-channel, Pwm Control Switching Regulator Controller
• Manufacturer: Seiko Instruments Inc.

Rev.2.3
STEP-UP, FOR LCD BIAS SUPPLY, 1-CHANNEL, PWM CONTROL SWITCHING REGULATOR CONTROLLER
4. External transistor
A bipolar (NPN) or enhancement (N-channel) MOS FET transistor can be used as the external capacitor.
4. 1 Bipolar (NPN) type
4. 2 Enhancement MOS FET type
_00
The driving capability when the output current is increased by using a bipolar transistor is determined by h
and R
1 k Ω is recommended for R
transistor as follows and select an R
A small R
a voltage drop occurs due to the wiring capacitance. Determine the optimum value by experiment.
A speed-up capacitor (C
switching loss and improves the efficiency.
Select C
However, in practice, the optimum C
transistor employed. Therefore, determine the optimum value of C
Use an Nch power MOS FET. For high efficiency, using a MOS FET with a low ON resistance (R
small input capacitance (C
trade-off relationship. The ON resistance is efficient in a range in which the output current is relatively great
during low-frequency switching, and the input capacitance is efficient in a range in which the output current
is middling during high-frequency switching.
capacitance are optimal depending on the usage conditions.
The input voltage (V
withstanding voltage that is equal to the maximum usage value of the input voltage or higher and a drain
withstanding voltage that is equal to the amount of the output voltage (V
higher.
If a MOS FET with a threshold that is near the UVLO detection voltage is used, a large current may flow,
stopping the output voltage from rising and possibly generating heat in the worst case. Select a MOS FET
with a threshold that is sufficiently lower than the UVLO detection voltage value.
I
R
C
b
b
=
b
=
≤
h
I
V
PK
FE
2
b
IN
of the bipolar transistor. Figure 11 shows a peripheral circuit.
π
− 0.7
b
I
R
b
b
by observing the following equation.
increases the output current, but the efficiency decreases. Actually, a pulsating current flows and
b
1
f
OSC
−
0
I
0.4
EXTH
7 .
IN
) is supplied for the gate voltage of the MOS FET, so select a MOS FET with a gate
b
) connected in parallel with R
ISS
b
. Actually, calculate the necessary base current (I
) is ideal, however, ON resistance and input capacitance generally share a
Figure 11 External Transistor Periphery
Pch
Nch
Seiko Instruments Inc.
b
b
value lower than this.
value also varies depending on the characteristics of the bipolar
V
IN
EXT
Select a MOS FET whose ON resistance and input
2200 pF
b
1 kΩ
C
R
resistance as shown in Figure 11 decreases the
b
b
b
by experiment.
I
PK
OUT
) and diode voltage (V
b
) from h
S-8333 Series
FE
of the bipolar
ON
) and
D
) or
15
FE