1.5A Low Dropout Positive Adjustable or Fixed-Mode Regulator

AP1086

Anachip Corp.

www.anachip.com.tw

Rev.1.3 Jun. 8, 2005

4/9

Functional Description

Introduction

The AP1086 adjustable or fixed-mode Low Dropout

(LDO) regulator is a 3 terminal device which can

easily be programmed by internal mask change to

any voltages within the range of 1.25V to Vin-1.4V.

The AP1086 only needs 1.4V differential between

Vin and Vout to 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 AP1086 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 AP1086 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 AP1086 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 AP1086 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

the Vout terminal of the device as possible. It is

recommended to use a section of a layer of the PC

board as a plane to connect the Vout pin to the

output capacitors to prevent any high frequency

oscillation that may result due to excessive trace

inductance.