AS1329B datasheet(7/17 Pages) AMSCO

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AS1329

Data Sheet - Deta iled Description

8 Detailed Description

The AS1329 can operate from a single-cell input voltage (VIN) below 1V, and features 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 device maintains 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 AS1329A, AS1329B and AS1329C 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 AS1329A as well as the AS1329B includes an auto-

matic 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 AS1329C does not support powersave mode and provides continuous operation at all loads, eliminating

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

Figure 15. Block Diagram

Low-Voltage Start-Up

The AS1329 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 AS1329 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.

AS1329

–

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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