S-8327 Seiko, S-8327 Datasheet - Page 16

• Manufacturer Part Number: S-8327
• Description: (S-8323 / S-8327) SMALL PACKAGE PWM CONTROL STEP-UP SWITCHING REGULATOR
• Manufacturer: Seiko

2. Diode
3. Capacitors (C
4. External transistor (S-8327 Series)
Use an external diode that meets the following requirements:








A capacitor at the input side (C
Select a C
A capacitor at the output side (C
(Electric Series Resistance) and a large capacitance. The capacitor value should be 10 F min. A tantalum electrolytic
capacitor and an organic semiconductor capacitor are especially recommended because of their superior low-temperature
characteristic and leakage current characteristic.
For the S-8327 Series, connecting an external transistor increases the output current. A bipolar (NPN) transistor or an
enhancement (N-channel) MOS FET transistor can be used as external transistor.
4.1. Bipolar (NPN) transistor
Low forward voltage:
High switching speed: (500 ns max.)
Reverse voltage:
Rated current:
A circuit example using a bipolar transistor (NPN), Sanyo 2SD1628G (h
value and the Rb value determine the driving capacity to increase the output current using a bipolar transistor. A
peripheral circuit example of the transistor is shown in Figure 8.
1 k
Cb is caluculated from the following formula:
A small Rb increases output current, however, the efficiency decreases.
The current flows pulsating and there is voltage drop due to wiring resistance in an actual circuit, therefore optimum Rb
value should be determined by experiment.
A speed-up capacitor connected in parallel with Rb resistance as shown in Figure 9 decreases the switching loss and
improves the efficiency.
IN
is recommended for Rb. Rb is caluculated from the following formula:
Rb=
Ib=IPK/h
value according to the impedance of the power supply used. The capacitor value should be around 10 F.
IN
, C
V
OUT
OUT
SMALL PACKAGE PWM CONTROL STEP-UP SWITCHING REGULATOR
Cb
)
FE
Ib
- 0.7
2
V
I
-
PK
(V
OUT
F
or more
IN
<0.3V)
Rb
+V
) improves the efficiency by reducing the power impedance and stabilizing the input current.
OUT
|I
1
EXTH
F
0.4
) is used for smoothing the ripple voltage. Therefore select a capacitor with a small ESR
or more
f
OSC
|
Pch
Nch
Figure 8 External transistor
V
Seiko Instruments Inc.
OUT
0.7
S-8327
EXT
2200pF
Cb
Rb
I
PK
FE
=280 to 560) is shown in Figure 11. The h
S-8323/8327 Series
15
FE