Rev.7.2
PWM Control & PWM/PFM Control
Step-Down Switching Regulator-Controllers
S-8520/8521 Series
The S-8520/8521 Series consists of CMOS step-down switching regulator-
controllers with PWM-control (S-8520) and PWM/PFM-switched control (S-
8521). These devices contain a reference voltage source, oscillation
circuit, error amplifier, and other components.
The S-8520 Series provides low-ripple power, high-efficiency, and
excellent transient characteristics thanks to a PWM control circuit capable
of varying the duty ratio linearly from 0% up to 100%. The series also
contains an error amplifier circuit as well as a soft-start circuit that prevents
overshoot at startup.
The S-8521 Series works with either PWM control or PFM control, and can
switch from one to the other. It normally operates using PWM control with
a duty ratio of 25% to 100%, but under a light load, it automatically
switches to PFM control with a duty ratio of 25%. This series ensures high
efficiency over a wide range of conditions, from standby mode to operation
of peripheral equipment.
With the addition of an external Pch Power MOS FET or PNP transistor, a coil,
capacitors, and a diode connected externally, these ICs can function as step-down
switching regulators. They serve as ideal power supply units for portable devices
when coupled with the SOT-23-5 minipackage, providing such outstanding
features as low current consumption. Since this series can accommodate an input
voltage of up to 16V, it is also ideal when operating via an AC adapter.
Features:
Applications:
•
On-board power supplies of battery devices for
portable telephones, electronic notebooks, PDAs, and
the like.
Power supplies for audio equipment, including portable
CD players and headphone stereo equipment.
Fixed voltage power supply for cameras, video
equipment and communications equipment.
Power supplies for microcomputers.
•
Low current consumption:
In operation: 60 µA max. (A & B Series)
21 µA max. (C & D Series)
100 µA max. (E & F Series)
When powered off: 0.5 µA max.
Input voltage:
2.5 V to 16 V (B, D, F Series)
2.5 V to 10 V (A, C, E Series)
Output voltage:
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Conversion from four NiH or NiCd cells or two lithium-
ion cells to 3.3 V/3 V.
Conversion of AC adapter input to 5 V/3 V.
Selectable between 1.5 V and
6.0 V in steps of 0.1 V.
Duty ratio:
•
0% to 100% PWM control (S-8520)
25% to 100% PWM/PFM-switched control (S-8521)
The only peripheral components that can be used with this IC are a Pch power MOS FET or PNP
transistor, a coil, a diode, and capacitors (If a PNP transistor is used, a base resistance and a capacitor
will also be required).
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Oscillation frequency: 180 kHz typ. (A & B Series), 60 kHz typ. (C & D Series), or 300 kHz typ. (E, F
Series).
Soft-start function: 8 msec. typ. (A & B Series) 12 msec. typ.(C & D Series), or 4.5 msec. typ. (E, F
Series).
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With a power-off function.
With a built-in overload protection circuit. Overload detection time: 4 msec. typ. (A Series), 14 msec. typ.
(C Series) or 2.6 msec. typ.(E, F Series).
Seiko Instruments Inc.
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