APL1117AUE-TRG データシートの表示（PDF） - Anpec Electronics

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APL1117AUE-TRG

1A Low Dropout Linear Regulator

Anpec Electronics 

APL1117A

Application Information

Output Voltage

The output voltage of the APL1117A-ADJ can be adjusted

with a resistive divider from output voltage to ADJ pin to

ground (see Figure1), and the internal reference voltage

is 1.25V. The following equation can be used to calculate

the output voltage:

VOUT = 1.25V × (1+ R2 ) + IADJ × R2

R1

Where the IADJ is a constant current flows through R2 and

represents a small error. Because the IADJ is very small, it

can usually be ignored. Note that the APL1117A-ADJ needs

a minimum load current of 10mA to present the output

voltage. For fixed voltage devices, the R1 and R2 are in-

cluded in the device.

APL1117A

VIN

VIN VOUT

VOUT

ADJ

VREF

R1

IADJ

60µA

R2

Figure 1. Basic Adjustable Regulator

Load Regulation

When the adjustable regulator is used, load regulation

will be limited by the resistance of the wire connecting the

regulator to the load. The datasheet specification for load

regulation is measured at the output pin of the device.

The best load regulation is obtained when the top of the

resistor divider (R1) is tied directly to the output pin of the

device, but to the load. For fixed voltage devices, the top of

R1 is internally connected to the output, and the ground

pin can be connected to low side of the load. If R1 is

connected to the load, RP is multiplied by the divider ratio,

the effective resistance between the regulator and the

load would be:

Rp

X

(1+

R2

R1

),

Rp

=

Parasitic

Line

Resistance

Rp

PARASITIC

APL1117A

LINE RESISTANCE

VIN

IN

OUT

ADJ

R1

RL

CONNECT

R1 TO CASE

R2

CONNECT

R2 TO LOAD

Figure 2. Connections for The Best Load Regulation

Input Capacitor

An input capacitor of 10µF or greater is recommended.

Tantalum or aluminum electrolytic capacitors can be used

for bypassing. Larger Values will improve ripple rejection

by bypassing the input to the regulator.

Output Capacitor

The APL1117A requires an output capacitor to maintain

stability and improve transient response. Proper capaci-

tor selection is important to ensure proper operation. The

APL1117A output capacitor selection depends upon the

ESR (equivalent series resistance) of the output capaci-

tor to maintain stability. When the output capacitor is 10µF

or greater, the output capacitor should have an ESR be-

tween 0.15Ω to 20Ω. This will improve transient response

as well as promote stability. A low-ESR solid tantalum

capacitor works extremely well and provides good tran-

sient response and stability over temperature.

Aluminum electrolytics can also be used, as long as the

ESR of the capacitor is less than1Ω. The value of the

output capacitor can be increased without limit. Higher

capacitance values help to improve transient response

and ripple rejection and reduce output noise.

Ripple Rejection

The curves for Ripple Rejection were generated by using

an adjustable device with the adjust pin bypassed. With a

22µF bypassing capacitor, 60dB ripple rejection is ob-

tainable at any output level. The impedance of the adjust

pin capacitor, at the ripple frequency, should be < R1. R1

Copyright © ANPEC Electronics Corp.

6

Rev. A.4 - May., 2010

www.anpec.com.tw

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