S-8520/8521 Series

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STEP-DOWN, PWM CONTROL or PWM / PFM SWITCHABLE

SWITCHING REGULATOR CONTROLLER

© SII Semiconductor Corporation, 1997-2010

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The S-8520/8521 Series is a CMOS step-down switching regulator-controller with PWM control (S-8520 Series) and PWM

/ PFM switching control (S-8521 Series). The S-8520/8521 Series has a reference voltage source, an oscillation circuit, an

error amplifier, and other components.

The S-8520 Series provides low-ripple power, high efficiency, and excellent transient characteristics due to a PWM control

circuit capable of varying the duty ratio linearly from 0% up to 100%. The S-8520/8521 Series also has a soft-start circuit

that prevents overshoot at startup.

The S-8521 Series works with either PWM control or PFM control. 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%. The S-8520/8521

Series ensures high efficiency over a wide range of conditions for devices, from the standby mode to the operation.

By adding external Pch power MOS FET or PNP transistor, coil, capacitor, and externally connected diode, the

S-8520/8521 Series can function as a step-down switching regulator, and is ideal for power supply units of portable

devices due to small SOT-23-5 and the feature of low current consumption. It is also ideal for AC adapters due to the input

voltage up to 16 V.

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Features

• Low current consumption During operation: 60 μA max. (A, B types)

21

μA max. (C, D types)

100

μA max. (E, F types)

During shutdown: 0.5

μA max.

• Input voltage:

2.5 V to 16 V (B, D, F types)

2.5 V to 10 V (A, C, E types)

• Output voltage:

Selectable between 1.5 V and 6.0 V in 0.1 V step

• Duty ratio:

0% to 100% PWM control (S-8520 Series)

25% to100% PWM / PFM switching control (S-8521 Series)

• External parts are Pch power MOS FET or PNP transistor, coil, diode, and capacitor only

(When using PNP transistor, add base resistor and capacitor).

• Oscillation frequency:

180 kHz typ. (A, B types)

60 kHz typ.

(C, D types)

300 kHz typ. (E, F types)

• Soft-start function:

8 ms. typ.

(A, B types)

12 ms. typ.

(C, D types)

4.5 ms. typ. (E, F types)

• With a shutdown function

• With a built-in overload protection circuit Overload detection time:

4 ms. typ.

(A type)

14 ms. typ.

(C type)

2.6 ms. typ. (E type)

*1. Refer to “ Product Name Structure” for details.