S-8331 Seiko Instruments USA, S-8331 Datasheet - Page 21

• Manufacturer Part Number: S-8331
• Description: Step-Up Switching Regulator (DC/DC Converter ICs)
• Manufacturer: Seiko Instruments USA

Rev.5.1
3. Diode
4. Capacitor (C
5. Externally-attached transistors (S-8331 Series)
5.1 Bipolar NPN type
Attaching a speed-up capacitor Cb to the resistor Rb reduces switching loss and increases the
efficiency.
Always use a diode which meets the following conditions.
Capacitor (C
stabilizing the input current. Select avalue (C
used.
The standard capacitance is approximately 10 μF. Select a capacitor (C
small ESR (Equivalent Series Resistance) and large capacitance to stabilize the ripple voltage. The
standard capacitance is approximately 10 μF.
electrolytic capacitor with excellent low temperature and leakage current characteristics.
The output current can be increased by externally attaching a transistor to the S-8331 Series. A bipolar
(NPN) type or an enhancement (Nch) MOS FET type of transistor can be used as an external transistor.
Figure 16 shows a circuit example using the 2SD1624 manufactured by Sanyo Electric Co., Ltd. as a
bipolar transistor (NPN). The drive ability to increase output current is determined by values h
of the bipolar transistor. A peripheral circuit example of the transistor is shown in Figure 13.
It is recommended to select value Rb of approximately 1 kΩ. Find necessary base current I
bipolar transistor h
and select small value Rb. Small value Rb can increase the output current, but may worsen the
efficiency. Also current may flow on the pulse or the voltage may drop due to wiring resistor. So, find
the optimum value with experiments.
Value Cb:
Rb
_00
Low forward voltage: V
Low switching speed: 500 ns max.
Reverse direction voltage: V
Rating current: I
=
V
IN
Ib
−
Cb
0
7 .
IN
≤
−
) at the input side improves the efficiency by reducing the power impedance and
IN
2
I
STEP-UP, FOR LCD BIAS SUPPLY, 1-CHANNEL SWITCHING REGULATOR
, C
0
π
EXTH
4 .
FE
×
OUT
Rb
PK
using I
or more.
)
×
Figure 13 External Transistor Peripheral Circuit
1
f
OSC
F
b
<0.3 V
=I
×
Pch
0
PK
Nch
7 .
OUT
/h
FE
+V
V
,
IN
S-8331
Seiko Instruments Inc.
F
or more
EXT
IN
) depending upon the impedance of the power supply
2200pF
It is particularly recommended to use a tantalum
Rb
1K
I
PK
OUT
S-8330/8331 Series
) at the output side with
www.DataSheet4U.com
b
FE
from the
and Rb
21