1.5A Low Dropout Positive Fixed-Mode Regulator

AP033

Anachip Corp.

www.anachip.com.tw

Rev.1.0 Aug.27, 2004

3/5

Typical Application

5V to 3.3V Fixed Mode Regulator

5V

3.3V/

1.5A

Tab is GND

GND

C2

100uF

C1

100uF

Function Description

Introduction

The AP033 fixed-mode Low Dropout (LDO)

regulator is a 3 terminal device. The AP033 only

maintain output regulation. In addition, the output

voltage tolerances are also extremely tight and they

include the transient response as part of the

specification. For example, Intel VRE specification

calls for a total of +/- 100mV including initial

tolerance, load regulation and 0 to 1.5A load step.

The AP033 is specifically designed to meet the fast

current transient needs as well as providing an

accurate initial voltage, reducing the overall system

cost with the need for fewer output capacitors.

Load Regulation

Since the AP033 is only a 3 terminal device, it is not

possible to provide true remote sensing of the

output voltage at the load. But it can supply good

load regulation by internal feedback bypass the

external loss such as adjustable mode.

Stability

The AP033 requires the use of an output capacitor

as part of the frequency compensation in order to

make the regulator stable. For most applications a

minimum of 10uF aluminum electrolytic capacitor

insures both stability and good transient response.

Thermal Design

The AP033 incorporates an internal thermal

shutdown that protects the device when the junction

temperature exceeds the maximum allowable

junction temperature. Although this device can

operate with junction temperatures in the range of

150

sink be chosen such that during maximum

continuous load operation the junction temperature

is kept below the temperature.

Layout Consideration

The output capacitors must be located as close to

recommended to use a section of a layer of the PC

output capacitors to prevent any high frequency

oscillation that may result due to excessive trace

inductance.