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AME, Inc.
5
AME1086
1.5A Low Dropout
Positive Voltage Regulator
n
Application Description
1. Output voltage adjustment
Like most regulators, the AME1086 regulates the
output by comparing the output voltage to an
internally generated reference voltage. On the
adjustable version, the V
REF
is available exter-
nally as 1.25V between V
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:
V
OUT
= V
REF
( 1 + ) + I
ADJ
x R2
On fixed versions of AME1086, the voltage divider
is provided internally.
R2
R1
Figure 3
2. Thermal protection
AME1086 has thermal protection which limits
junction temperature to 150
O
C. However, de-
vice
functionality is only guaranteed to a maxi-
mum junction temperature of +125
O
C.
The power dissipation and junction temperature
for AME1086 in TO-220 package are given by
P
D
= (V
IN
- V
OUT
) x I
T
JUNCTION
= T
AMBIENT
+ ( P
D
x
θ
JA
)
Note: T
JUNCTION
must not exceed 125
O
C
3. Current limit protection
AME1086 is protected against overload condi-
tions. Current protection is triggered at typi-
cally 3.0A.
4. Stability and load regulation
AME1086 requires a capacitor from V
OUT
to GND
to provide compensation feedback to the inter-
nal
gain stage. This is to ensure stability at
the output terminal. Typically, a 10
μ
F tantalum
or
50
μ
F aluminum electrolytic is sufficient.
Note: It is important that the ESR for this ca-
pacitor does not exceed 0.5
.
The output capacitor dose not have a theoreti-
cal upper limit and increasing its value will in-
creasestability. C
OUT
= 100
μ
F or more is typi-
cal for high current regulator design.
For the adjustable version, the best load regu-
lation is accomplished when the top of the
resistor divider (R1) is connected directly to the
output pin of the AME1086. When so con-
nected, R
is not multiplied by the divider ratio.
For fixed output versions, the top of R1 is in-
ternally connected to the output and ground
pin can be connected to low side of the load.
Figure 4
V
OUT
= V
REF
(1+R2
R1
) + I
ADJ
x R2
OUT
ADJ
IN
V
REF
I
ADJ
50
A
V
IN
V
OUT
R1
R2
C
1
OUT
ADJ
IN
V
IN
R1
R2
R
L
R
Parasitic
Line Resistance
Connect
R2 to load
(Connect R1 to case)