s-8521b51mc-aukt2g Seiko Instruments Inc., s-8521b51mc-aukt2g Datasheet - Page 20

• Manufacturer Part Number: s-8521b51mc-aukt2g
• Description: Step-down, Pwm Control Or Pwm / Pfm Switchable Switching Regulator Controller
• Manufacturer: Seiko Instruments Inc.

20
STEP-DOWN, PWM CONTROL or PWM / PFM SWITCHABLE SWITCHING REGULATOR CONTROLLOR
S-8520 / 8521 Series
5. 2 Bipolar PNP type
Figure 11 shows a sample circuit diagram using Toshiba Corporation 2SA1213-Y for the bipolar
transistor (PNP).
transistor is determined by the h
The R
Find the necessary base current (I
A small R
affect the efficiency. Moreover, in practice, a current may flow as the pulses or a voltage drop may
take place due to the wiring resistance or some other reason. Determine an optimum value through
experimentation.
In addition, if speed-up capacitor (C
the switching loss will be reduced, leading to a higher efficiency.
Select a C
Select a C
upon the characteristics of the bipolar transistor.
R
I =
C
b
b
b
=
≤
h
I
PK
2
V
FE
b
π
-value is given by the following equation:
IN
, and select a smaller R
×
I
−
b
R
b
b
0
b
b
value by using the following equation as a guide:
7 .
value will certainly contribute to increasing the output current, but it will also adversely
value after performing sufficient evaluation since the optimum C
×
1
f
−
osc
I
EXTL
0
×
4 .
0
The driving capacity for increasing the output current by means of a bipolar
7 .
b
FE
value.
value and the R
Toshiba Corporation
b
) is inserted in parallel with resistance R
b
R
V
) using the (h
IN
b
2SA1213-Y
Seiko Instruments Inc.
Figure 11
C
EXT
VIN
b
b
value of that bipolar transistor.
FE
) value of bipolar transistor by the equation,
b
b
, as shown in Figure 11 ,
value differs depending
Rev.8.3
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