APL1541-33KC-TR ANPEC [Anpec Electronics Coropration], APL1541-33KC-TR Datasheet - Page 8

• Manufacturer Part Number: APL1541-33KC-TR
• Description: 1A Low Dropout Fast Response Positive Adjustable Regulator and Fixed 3.3V
• Manufacturer: ANPEC [Anpec Electronics Coropration]

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.
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+
V
IN
Figure 1. Basic Adjustable Regulator
V
R2
R1
O U T
), Rp = Parasitic Line Resistance
= V
IN
60 A
R E F
APL1541
I
ADJ
(1+
ADJ
R 2
OUT
R 1
)+I
A D J
R 2
V
REF
R1
R2
V
OUT
V
An input capacitor of 10 F 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.
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 1 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.
IN
Figure 2. Connections for Best Load Regulation
IN
A P L 1 5 4 1
A D J
O U T
L IN E R E S IS T A N C E
R 1
R 2
P A R A S IT IC
R 1 T O C A S E
R 2 T O L O A D
C O N N E C T
C O N N E C T
R p
R
L