AME1085 Datasheet, PDF (5/14 Pages) Analog Microelectronics – 3A Low Dropout Positive Voltage Regulator

Analog Microelectronics, Inc.
AME1085
3A Low Dropout
Positive Voltage Regulator
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 VREF 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:
V_OUT = V_REF ( 1 +
R2
R1
) + I_ADJ x R2
On fixed versions of AME1085, the voltage di-
vider is provided internally.
V _IN
C₁
IN
OUT
ADJ
I_ADJ
5 0 µA
V_REF
V_OUT
R1
R2
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 VOUT 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. COUT = 100µF 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 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.
V_OUT
=
V_REF
(1+
R2
R1
)
+
I_ADJ
x
R2
Figure 3
V _IN
2. Thermal protection
AME1085 has thermal protection which limits
junction temperature to 150^OC. However, de-
vice functionality is only guaranteed to a maxi-
mum junction temperature of +125^OC.
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^OC
R_P
Parasitic
Line Resistance
IN
OUT
ADJ
R1
R_L
(Connect R1 to case)
R2
Connect
R2 to load
Figure 4
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