S-8521A25MC-AXK-T2 Seiko Instruments, S-8521A25MC-AXK-T2 Datasheet - Page 20

• Manufacturer Part Number: S-8521A25MC-AXK-T2
• Description: DC/DC Switching Regulators 2.5V 60uA Step-Down
• Manufacturer: Seiko Instruments

Specifications of S-8521A25MC-AXK-T2

• Output Voltage: 2.5 V
• Output Current: 120 mA
• Input Voltage: 2.5 V to 10 V
• Duty Cycle (max): 100 %
• Switching Frequency: 180 KHz
• Mounting Style: SMD/SMT
• Package / Case: SOT-23-5
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

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STEP-DOWN, PWM CONTROL or PWM / PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8520/8521 Series
5. 2 Bipolar PNP type
Figure 11 shows the sample of circuit diagram using Toshiba Corporation 2SA1213 as the bipolar transistor
(PNP). The h
increasing the output current.
The R
Calculate the necessary base current (I
and select a smaller R
A small R
through experiment, since the base current may flow on the pulse, or voltage may drop due to wiring resistance.
In addition, if speed-up capacitor C
switching will be reduced, leading to higher efficiency.
Determine the C
C
Select the C
characteristics of the bipolar transistor.
b
R
≤
b
=
2 × π × R
b
value is given by the following equation:
V
IN
b
value increases the output current, but it also decreases efficiency. Determine the optimum value
− 0.7
I
b
b
FE
value after performing sufficient evaluation since the optimum C
b
1
value and the R
× f
b
value using the following equation:
osc
−
× 0.7
b
I
0.4
EXTL
value.
Toshiba Corporation
b
R
V
value of that bipolar transistor determine the driving capacity, which is used for
b
IN
2SA1213
b
is connected in parallel with resistor R
Seiko Instruments Inc.
b
) using the (h
C
Figure 11
EXT
b
VIN
FE
) value of bipolar transistor by the equation, I
b
, as shown in Figure 11, the loss in
b
value differs depending upon the
Rev.9.0
b
=
h
I
_00
PK
FE
,