s-8337aaca-t8t1g Seiko Instruments Inc., s-8337aaca-t8t1g Datasheet - Page 17

• Manufacturer Part Number: s-8337aaca-t8t1g
• Description: Step-up, 1.2 Mhz High-frequency, Pwm Control Switching Regulator Controller
• Manufacturer: Seiko Instruments Inc.

Rev.3.1
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
_00
STEP-UP, 1.2 MHz HIGH-FREQUENCY, PWM CONTROL SWITCHING REGULATOR CONTROLLER
The driving capability when the output current is increased by using a bipolar transistor is
determined by h
1 kΩ is recommended for R
bipolar transistor as follows and select an R
A small R
current flows and a voltage drop occurs due to the wiring capacitance. Determine the optimum
value by experiment.
A speed-up capacitor (C
decreases the switching loss and improves the efficiency.
Select C
However, in practice, the optimum C
bipolar transistor employed. Therefore, determine the optimum value of C
I
R
C
b
b
b
=
=
≤
2π • R
V
h
I
PK
FE
IN
b
– 0.7
I
b
b
by observing the following equation.
increases the output current, but the efficiency decreases. Actually, a pulsating
b
• f
1
OSC
–
FE
I
and R
0.4
• 0.7
EXTH
b
b
) connected in parallel with R
of the bipolar transistor. Figure 11 shows a peripheral circuit.
Figure 11 External Transistor Periphery
Seiko Instruments Inc.
b
. Actually, calculate the necessary base current (I
Pch
Nch
V
IN
b
value also varies depending on the characteristics of the
EXT
b
value lower than this.
2200 pF
1 kΩ
C
R
b
b
b
resistance as shown in Figure 11
I
PK
S-8337/8338 Series
b
by experiment.
b
) from h
FE
of the
17