APL1117-25 データシートの表示（PDF） - Anpec Electronics

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APL1117-25

1A Low Dropout Fast Response Positive Adjustable Regulator and Fixed 1.2V,1.8V, 2.5V, 2.85V, 3.3V and 5V

Anpec Electronics 

APL1117

Application Information

Output Voltage

The APL1117 develops a 1.25V reference voltage between

the output and the adjust terminal. By placing a resistor

VIN

between these two terminals, a constant Current is caused

to flow through R1 and down through R2 to set the overall

output voltage. Normally, this current is chosen to be the

specified minimum load current of 10mA. For fixed volt-

age devices R1 and R2 are included in the device.

APL1117

IN OUT

ADJ

Rp

PARASITIC

LINE RESISTANCE

R1

RL

CONNECT

R1 TO CASE

R2

APL1117

VIN

IN

OUT

ADJ

VREF

IADJ

60µA

VOUT = V REF(1+ RR21)+IADJR2

VOUT

R1

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 data sheet specification for load

regulation is measured at the output pin of the device.

Best load regulation is obtained when the top of the re-

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

device not 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, R is multiplied by the divider ratio,

P

the effective resistance between the regulator and the

load would be:

Rp

X

(1+

R2

R1

),

Rp

=

Parasitic

Line

Resistance

CONNECT

R2 TO LOAD

Figure 2. Connections for 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 APL1117 requires an output capacitor to maintain sta-

bility and improve transient response. Proper capacitor

selection is important to ensure proper operation. The

APL1117 output capacitor selection is dependent upon

the ESR (equivalent series resistance) of the output ca-

pacitor to maintain stability. When the output capacitor is

10µF or greater, the output capacitor should have an ESR

less than 1Ω. This will improve transient response as

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

pacitor works extremely well and provides good transient

response and stability over temperature.

Aluminum electrolytics can also be used, as long as the

ESR of the capacitor is <1Ω. The value of the output ca-

pacitor can be increased without limit. Higher capacitance

values help to improve transient response and ripple re-

jection and reduce output noise.

Copyright © ANPEC Electronics Corp.

9

Rev. C.10 - Sep., 2010

www.anpec.com.tw

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