AME1085AMCT datasheet(5/14 Pages) AME

5 / 14 page

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:

OUT = VREF ( 1 +

) + I

ADJ x R2

On fixed versions of AME1085, the voltage di-

vider is provided internally.

Figure 3

2. Thermal protection

AME1085 has thermal protection which limits

junction temperature to 150OC. However, de-

vice

functionality is only guaranteed to a maxi-

mum junction temperature of +125OC.

The power dissipation and junction temperature

for AME1085 in TO-220 package are given by

D = (VIN - VOUT) x IOUT

JUNCTION = TAMBIENT + ( PD x θJA)

Note: T

JUNCTION must not exceed 125

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 10

µF tanta-

lum or 50

µF aluminum electrolytic is sufficient.

Note: It is important that the ESR for this ca-

pacitor does not exceed 0.5

Ω.

The output capacitor dose not have a theoreti-

cal upper limit and increasing its value will in-

crease stability. COUT = 100

µF 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.

Figure 4

OUT = V REF (1+

) + I

ADJ x R2

OUT

ADJ

REF

AD J

µA

OUT

ADJ

Parasitic

Line Resistance

Connect

R2 to load

(Connect R1 to case)

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