APL1541 データシートの表示（PDF） - Anpec Electronics
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APL1541 Datasheet PDF : 13 Pages
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APL1541
Application Information
Output Voltage
The APL1541 develops a 1.25V reference voltage be-
tween the output and the adjust terminal. By placing
a resistor 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 voltage devices R1 and R2
are included in the device.
APL1541
V
IN
IN
OUT
V
OUT
ADJ
VREF
R1
IADJ
60µA
R2
VOUT
=
VREF(1+
R
R
21)+
IA
D
J
R
2
Figure 1. Basic Adjustable Regulator
Load Regulation
Rp
P A R A S IT IC
APL1541
LINE RESISTANCE
V
IN
IN
OUT
ADJ
R1
RL
CONNECT
R1 TO CASE
R2
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.
When the adjustable regulator is used. Load regula-
tion will be limited by the resistance of the wire con-
necting the regulator to the load. The data sheet speci-
fication for load regulation is measured at the output
pin of the device. Best load regulation is obtained
when the top of the resistor 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 con-
nected to the output, and the ground pin can be con-
nected to low side of the load. If R1 were 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+ RR21), Rp = Parasitic Line Resistance
Output Capacitor
The APL1541 requires an output capacitor to main-
tain stability and improve transient response. Proper
capacitor selection is important to ensure proper
operation. The APL1541 output capacitor selection
is dependent upon the ESR (equivalent series
resistance) of the output capacitor to maintain stability.
When the output capacitor is 10uF or greater, the out-
put capacitor should have an ESR less than 1Ω.This
will improve transient response as well as promote
stability. A low-ESR solid tantalum capacitor works
extremely well and provides good transient response
and stability over temperature.
Copyright ANPEC Electronics Corp.
8
Rev. A.2 - Oct., 2003
www.anpec.com.tw
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