AME, Inc.
AME1117
n
Application Description
1. Output Voltage Adjustment
Like most regulators, the AME1117 regulates the out-
put by comparing the output voltage to an internally gen-
erated reference voltage. On the adjustable version, the
V
REF
is available externally as 1.25V between V
OUT
and
ADJ. The voltage ratio formed by R1 and R2 should be
set to conduct 10mA (minimum output load). The output
voltage is given by the following equation:
R2
V
OUT
= V
REF
( 1 +
) + I
ADJ
x R2
R1
On fixed versions of AME1117, the voltage divider is
provided internally.
3. Current Limit Protection
AME1117 is protected against overload conditions. Cur-
rent protection is triggered at typically 1.5A.
4. Stability and Load Regulation
AME1117 requires a capacitor from V
OUT
to GND to pro-
vide compensation feedback to the internal gain stage.
This is to ensure stability at the output terminal. Typi-
cally, a 10µF tantalum or 50µF aluminum electrolytic is
sufficient.
(Note: It is important that the ESR for this capacitor does not ex-
ceed 0.5Ω.)
1A Low Dropout
Positive Voltage Regulator
V
IN
IN
ADJ
C
1
I
ADJ
55µA
OUT
V
REF
V
OUT
The output capacitor does not have a theoretical upper
limit and increasing its value will increase stability. C
OUT
= 100µF or more is typical for high current regulator de-
sign.
For the adjustable version, the best load regulation is
accomplished when the top of the resistor divider (R1) is
connected directly to the output pin of the AME1117.
When so connected, R
P
is not multiplied by the divider
ratio.
For fixed output versions, the top of R1 is internally
connected to the output. The ground pin can be connected
to the low side of the load in order to eliminate ground
loop errors.
R
P
Parasitic
Line Resistance
IN
ADJ
R1
(Connect R1 to case)
R
L
OUT
R1
R2
V
OUT
= V
REF
(1+R2 ) + I
ADJ
x R2
R1
2. Thermal Protection
AME1117 has thermal protection which limits junction
temperature to 150
o
C. However, device functionality is
only guaranteed to a maximum junction temperature of
+125
o
C.
The power dissipation and junction temperature for
AME1117 is given by
P
D
= (V
IN
- V
OUT
) x I
OUT
T
JUNCTION
= T
AMBIENT
+ ( P
D
x
θ
JA
)
Note: T
JUNCTION
must not exceed 125
o
C
V
IN
R2
Connect
R2 to load
10
Rev.S.02
AME [ ANALOG MICROELECTRONICS ]
