Analog Microelectronics, Inc.
AME1085
3A Low Dropout
Positive Voltage Regulator
n
General Description
The AME1085 is a 3A low-dropout positive voltage regu-
lator. It is available in fixed and adjustable output voltage
versions. Overcurrent and thermal protection are inte-
grated onto the chip. Output current will limit as it reaches
the pre-set current or temperature limit. At full rated
output current the dropout voltage is 1.4V (max.).
AME1085 series regulators provide excellent regulation
over line, load and temperature variations.
n
Key Features
l
l
l
l
l
l
l
l
Low dropout voltage 1.2V typically at 3A
Adjustable or 3.3V fixed voltage
Line regulation typically 0.015%
Load regulation typically 0.05%
Adjust pin (ADJ) current less than 90υA
Overcurrent protection
Thermal protection
Available in TO-220, TO-263, TO-252
n
Applications
l
l
l
l
High Efficiency Linear Regulators
Post Regulators for Switching Supplies
5V to 3.3V Voltage Converter
Battery Charger
n
Functional Block Diagram
Input
n
Typical Application
AME1085
V
IN
GND
V
OUT
Current
Limiting
Amplifier
Thermal
Protection
Output
4.75V to 5.25V
10µF Tan
10µF Tan
L o a d
Error
Amp.
Bandgap
Reference
ADJ/GND
Figure 2
Figure 1
1
Analog Microelectronics, Inc.
AME1085
3A Low Dropout
Positive Voltage Regulator
3. Current limit protection
AME1085 is protected against overload condi-
tions. Current protection is triggered at typi-
cally 4.5A.
4. Stability and load regulation
AME1085 requires a capacitor from V
OUT
to
GND to provide compensation feedback to the
internal gain stage. This is to ensure stability
at the output terminal. Typically, a 10µF tanta-
lum or 50µF aluminum electrolytic is sufficient.
Note: It is important that the ESR for this ca-
pacitor does not exceed 0.5Ω.
The output capacitor dose not have a theoreti-
cal upper limit and increasing its value will in-
crease stability. C
OUT
= 100µF or more is typi-
cal for high current regulator design.
V
OUT
V
REF
R1
n
Application Description
1. Output voltage adjustment
Like most regulators, the AME1085 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
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
) + I
ADJ
x R2
V
OUT
= V
REF
( 1 +
R1
On fixed versions of AME1085, the voltage di-
vider is provided internally.
V
IN
C
1
IN
ADJ
I
A DJ
50µA
OUT
R2
V
O U T
= V
R E F
(1+ R 2 ) + I
ADJ
x R2
R1
V
IN
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 AME1085. When so con-
nected, R
P
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.
R
P
Parasitic
Line Resistance
IN
ADJ
OUT
Figure 3
2. Thermal protection
AME1085 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 AME1085 in TO-220 package are 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
R1
(Connect R1 to case)
R
L
R2
Connect
R2 to load
Figure 4
5
Microcontroller MCU
京公网安备 11010802033920号
EEWORLD
