S-8520 Seiko Instruments, S-8520 Datasheet - Page 14

• Manufacturer Part Number: S-8520
• Description: (S-8520 / S-8521) PWM Control and PFM Control Step DOwn Switching Regulator Controllers
• Manufacturer: Seiko Instruments

PWM Control & PWM/PFM Control Step-Down Switching Regulator-Controllers
S-8520/8521 Series
14
Standard Circuits:
(1) Using a bipolar transistor:
(2) Using a Pch MOS-FET transistor
Precautions:
Install the external capacitors, diode, coil, and other peripheral components as close to the IC as possible,
and secure grounding at a single location.
Any switching regulator intrinsically produces a ripple voltage and spike noise, which are largely dictated by
the coil and capacitors in use. When designing a circuit, first test them on actual equipment.
The overload protection circuit of this IC performs the protective function by detecting the maximum duty
time (100 %). In choosing the components, make sure that overcurrents generated by short-circuits in the
load, etc., will not surpass the allowable dissipation of the switching transistor and inductor.
Make sure that dissipation of the switching transistor will not surpass the allowable dissipation of the
package. (especially at the time of high temperature)
V
IN
V
IN
Figure 10 Power dissipation of an SOT-23-5 Package (Free-Air)
C
IN
C
IN
R
SD
Tr
b
ON / OFF
Seiko Instruments Inc.
Tr
ON / OFF
SD
(mW)
C
P
b
EXT
VIN
D
VIN
EXT
200
100
0
0
Figure 9
Temperature Ta (
Figure 8
50
Oscillation
Circuit
Oscillation
Circuit
PWM or
PWM/PFM-
Switched Control
Circuit
PWM or
PWM/PFM-
Switched Control
Circuit
VSS
100
VSS
0
Reference Voltage
Source with Soft-Start
C)
L
V
Reference Voltage
Source with Soft-Start
ON / OFF
L
V
ON / OFF
150
−
+
+
−
VOUT
VOUT
C
OUT
C
OUT
Rev.7.4
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