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AS1322

Data Sheet - Deta iled Description

8 Detailed Description

The AS1322/AS1322B can operate from a single-cell input voltage (VIN) below 1V, and feature fixed frequency

(1.2MHz) and current mode PWM control for exceptional line- and load-regulation. With low RDS(ON) and gate charge

internal NMOS and PMOS switches, the devices maintain high-efficiency from light to heavy loads.

Modern portable devices frequently spend extended time in low-power or standby modes, switching to high power-

drain only when certain functions are enabled. The AS1322A and the AS1322B are ideal for portable devices since

they maintain high-power conversion efficiency over a wide output power range, thus increasing battery life in these

types of devices.

In addition to high-efficiency at moderate and heavy loads, the AS1322A includes an automatic powersave mode that

improves efficiency of the power converter at light loads. The powersave mode is initiated if the output load current

falls below a factory programmed threshold (see Figure 3 on page 5).

Note: The AS1322B does not support powersave mode and provides continuous operation at light loads, eliminating

low-frequency VOUT ripple at the expense of light load efficiency.

Figure 15. Block Diagram

Low-Voltage Start-Up

The AS1322 requires VIN of only 0.85V (typ) or higher to start up. The low-voltage start-up circuitry controls the internal

NMOS switch up to a maximum peak inductor current of 850mA (typ), with 1.5ms (approx.) off-time during start-up,

allowing the devices to start up into an output load.

With a VOUT > 2.3V, the start-up circuitry is disabled and normal fixed-frequency PWM operation is initiated. In this

mode, the AS1322 operates independent of VIN, allowing extended operating time as the battery can drop to several

tenths of a volt without affecting output regulation. The limiting factor for the application is the ability of the battery to

supply sufficient energy to the output.

AS1322

–

Start Up

OSC

PWM

Control

A/B

MUX

Slope

Compensator

1.2MHz

Ramp

Generator

–

Powersave

Operation

Control

–

Shutdown

Control

PWM

Comp

–

1.23V

Ref

Sync Drive

Control

VOUT

Good

2.3V

gm Error

Amp

Shutdown

Powersave

0.35

0.45

640k

1.02M

CFF*

COUT

4.7µF

3.3V

Output

CIN

1µF

1.5V

Single

Cell

* Optional

Current

Sense

80k

CP2

2.5pF

150pF

GND

SHDNN

VIN

VOUT

4.7µH

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