AAT3236 Ver la hoja de datos (PDF) - Analog Technology Inc

Número de pieza

componentes Descripción

Lista de partido

AAT3236

300mA CMOS High Performance LDO

Analog Technology Inc 

AAT3236

300mA CMOS High Performance LDO

Applications Information

Input Capacitor

Typically a 1µF or larger capacitor is recommend-

ed for CIN in most applications. A CIN capacitor is

not required for basic LDO regulator operation.

However, if the AAT3236 is physically located more

than 6 centimeters from an input power source, a

CIN capacitor will be needed for stable operation.

CIN should be located as close to the device VIN pin

as practically possible. CIN values greater than

1µF will offer superior input line transient response

and will assist in maximizing the highest possible

power supply ripple rejection.

Ceramic, tantalum or aluminum electrolytic capaci-

tors may be selected for CIN. There is no specific

capacitor ESR requirement for CIN. However, for

300mA LDO regulator output operation, ceramic

capacitors are recommended for CIN due to their

inherent capability over tantalum capacitors to with-

stand input current surges from low impedance

sources such as batteries in portable devices.

Output Capacitor

For proper load voltage regulation and operational

stability, a capacitor is required between pins VOUT

and GND. The COUT capacitor connection to

the LDO regulator ground pin should be made as

direct as practically possible for maximum device

performance.

The AAT3236 has been specifically designed to

function with very low ESR ceramic capacitors.

Although the device is intended to operate with

these low ESR capacitors, it is stable over a very

wide range of capacitor ESR, thus it will also work

with higher ESR tantalum or aluminum electrolytic

capacitors. However, for best performance,

ceramic capacitors are recommended.

Typical output capacitor values for maximum out-

put current conditions range from 1µF to 10µF.

Applications utilizing the exceptionally low output

noise and optimum power supply ripple rejection

characteristics of the AAT3236 should use 2.2µF or

greater for COUT. If desired, COUT may be

increased without limit.

In low output current applications where output

load is less then 10mA, the minimum value for

COUT can be as low as 0.47µF.

8

Bypass Capacitor and Low Noise

Applications

A bypass capacitor pin is provided to enhance the

very low noise characteristics of the AAT3236 LDO

regulator. The bypass capacitor is not necessary for

operation of the AAT3236. However, for best device

performance, a small ceramic capacitor should be

placed between the Bypass pin (BYP) and the device

ground pin (GND). The value of CBYP may range

from 470pF to 10nF. For lowest noise and best pos-

sible power supply ripple rejection performance a

10nF capacitor should be used. To practically realize

the highest power supply ripple rejection and lowest

output noise performance, it is critical that the capac-

itor connection between the BYP pin and GND pin be

direct and PCB traces should be as short as possi-

ble. Refer to the PCB Layout Recommendations

section of this document for examples.

There is a relationship between the bypass capac-

itor value and the LDO regulator turn on time. In

applications where fast device turn on time is

desired, the value of CBYP should be reduced.

In applications where low noise performance

and/or ripple rejection are less of a concern, the

bypass capacitor may be omitted. The fastest

device turn on time will be realized when no bypass

capacitor is used.

DC leakage on this pin can affect the LDO regula-

tor output noise and voltage regulation perform-

ance. For this reason, the use of a low leakage,

high quality ceramic (NPO or COG type) or film

capacitor is highly recommended.

Capacitor Characteristics

Ceramic composition capacitors are highly recom-

mended over all other types of capacitors for use

with the AAT3236. Ceramic capacitors offer many

advantages over their tantalum and aluminum elec-

trolytic counterparts. A ceramic capacitor typically

has very low ESR, is lower cost, has a smaller PCB

footprint and is non-polarized. Line and load tran-

sient response of the LDO regulator is improved by

using low ESR ceramic capacitors. Since ceramic

capacitors are non-polarized, they are not prone to

incorrect connection damage.

Equivalent Series Resistance (ESR): ESR is a very

important characteristic to consider when selecting a

capacitor. ESR is the internal series resistance asso-

3236.2001.11.0.9

Share Link: