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AS1323

Datasheet - Detailed Descr i pti on

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 efficiency by minimizing losses (see Synchronous Rectification on page 8). The AS1323 also

features an active-low shutdown circuit that supply current to 0.1µA.

Figure 20. Block Diagram

8.1 PFM Control

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

efficiency over a wide output current-range. Rather than using an integrated oscillator, the inductor 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.

8.2 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.

8.3 Low-Voltage Startup Circuit

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

8.4 Shutdown

The AS1323 enter shutdown when the SHDNN pin is driven low. During shutdown, the output is completely disconnected from the battery.

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