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AS1333

Data Sheet - D e t a i l e d D e s c r i p t i o n

8 Detailed Description

The AS1333 is a simple, step-down DC-DC converter optimized for powering portable applications that require low

dropout voltages such as mobile phones, portable communicators, and similar battery powered RFIC devices. Besides

being packed with numerous features like current overload protection, thermal overload shutdown and soft start,

AS1333 displays the following characteristics:

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Its operation is based on current-mode buck architecture with synchronous rectification for high efficiency.

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Allows the application to operate at maximum efficiency over a wide range of power levels from a single Li-Ion bat-

tery cell.

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Provides for a maximum load capability of 650mA in PWM mode, wherein the maximum load range may vary

depending on input voltage, output voltage and the selected inductor.

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Is ranked at an efficiency of around 96% for a 400mA load with a 3.6V input and a fixed output voltage of 3.09V.

Figure 22. Functional Block Diagram

AS1333 is fabricated using a chip-scale 8-pin WL-CSP package, which requires special design considerations for

implementation. Its fine bumppitch requires careful board design and precision assembly equipment. This package

offers the smallest possible size, for space-critical applications such as cell phones, where board area is an important

design consideration. The size of the external components is reduced by using a high switching frequency (2MHz).

Figure 1 on page 1 demonstrates that only three external power components are required for implementation. The WL-

CSP package is appropriate for opaque case applications, where its edges are not subject to highintensity ambient red

or infrared light. Also, the system controller should set EN low during power-up and other low supply voltage

conditions. See Shutdown Mode on page 11.

Mosfet

Control

Logic

Shutdown

Control

Main Control

Soft Start

Oscillator

Current

Sense

VDD

FB

NC

EN

SW

AGND

PGND

AS1333