AS1329 datasheet(8/20 Pages) AMSCO

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AS1329

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

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 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 6 on page 5).

Note:

The AS1329C does not support powersave mode and provides continuous operation at all loads, eliminating low-frequency VOUT rip-

ple at the expense of light load efficiency.

Figure 19. AS1329 - Block Diagram

8.1 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

Ω

0.45

Ω

640k

Ω 1%

1.02M

Ω

CFF*

COUT

4.7µF

3.3V

Output

CIN

1µF

1.5V

Single Cell

* Optional

Current

Sense

80k

Ω

CP2

2.5pF

150pF

GND

SHDNN

VIN

VOUT

4.7µH

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