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AS1323

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 AS1323 is a compact, high-efficiency, step-up DC-DC converter guaranteed to start up with voltages as low as

0.95V, and operate with an input voltage down to 0.75V. Consuming only 1.6µA of quiescent current, the device

includes an integrated synchronous rectifier that eliminates the need for an external diode and improves overall effi-

ciency by minimizing losses (see Synchronous Rectification on page 8). The AS1323 also features an active-low shut-

down circuit that supply current to 0.1µA.

Figure 19. Block Diagram

PFM Control

A forced discontinuous, current-limited, pulse-frequency modulation (PFM) control scheme provides ultra-low quies-

cent current and high efficiency over a wide output current-range. Rather than using an integrated oscillator, the induc-

tor current is limited by the 400mA N-channel current limit or by the 6µs switch maximum on-time. After each device-on

cycle, the inductor current must ramp to zero before another cycle can start. When the error comparator senses that

the output has fallen below the regulation threshold, another cycle can begin.

Synchronous Rectification

The integrated synchronous rectifier eliminates the need for an external Schottky diode, reducing cost and PCB space.

During normal operation, while the inductor discharges, the P-channel MOSFET turns on and shunts the MOSFET

body diode. Consequently the rectifier voltage drop is significantly reduced improving efficiency without the need for

external components.

Low-Voltage Startup Circuit

The AS1323 contains a unique low-voltage startup circuit which ensures start-up even with very high load currents.

startup at input voltages as low as 0.95V.

Shutdown

The AS1323 enter shutdown when the SHDNN pin is driven low. During shutdown, the output is completely discon-

normal operation, connect SHDN to the input.

AS1323

4

VOUT

3

SHDNN

Ref

5

LX

Control

Logic

Startup

System

Timing

2

VSS

Comparator

Voltage

L1

Comparator

Discharge

Comparator

Charge

1

VBATT

0.95 to

1.6V