AMS1084 Advanced Monolithic Systems, AMS1084 Datasheet - Page 5

• Manufacturer Part Number: AMS1084
• Description: 5A LOW DROPOUT VOLTAGE REGULATOR
• Manufacturer: Advanced Monolithic Systems

APPLICATION HINTS
This current is normally the specified minimum load current of
10mA. Because I
small error and it can usually be ignored.
Load Regulation
True remote load sensing it is not possible to provide, because the
AMS1084 is a three terminal device. The resistance of the wire
connecting the regulator to the load will limit the load regulation.
The data sheet specification for load regulation is measured at the
bottom of the package. Negative side sensing is a true Kelvin
connection, with the bottom of the output divider returned to the
negative side of the load.
The best load regulation is obtained when the top of the resistor
divider R1 is connected directly to the case not to the load. If R1
were connected to the load, the effective resistance between the
regulator and the load would be:
*
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone [phone] Fax [phone]
CONNECT R1 TO CASE
CONNECT R2 TO LOAD
V
V
IN
Figure 2. Connections for Best Load Regulation
IN
R
P
Figure 1. Basic Adjustable Regulator
x ( R2+R1 ) ,
V
IN
ADJ
AMS1084
OUT
R1
ADJ
is very small and constant it represents a
= V
OUT
IN
AMS1084
I
50 A
ADJ
REF
ADJ
1+ R2/R1)+I
R
OUT
LINE RESISTANCE
P
= Parasitic Line Resistance
R1*
R2*
PARASITIC
R
V
P
REF
ADJ
R2
R1
R2
V
OUT
R
L
Connected as shown, R
Using 16-gauge wire the parasitic line resistance is about 0.004
per foot, translating to 4mV/ft at 1A load current. It is important
to keep the positive lead between regulator and load as short as
possible and use large wire or PC board traces.
Thermal Considerations
The AMS1084 series have internal power and thermal limiting
circuitry designed to protect the device under overload
conditions. However maximum junction temperature ratings
should not be exceeded under continuous normal load conditions.
Careful consideration must be given to all sources of thermal
resistance from junction to ambient, including junction-to-case,
case-to-heat sink interface and heat sink resistance itself. To
ensure safe operating temperatures and reflect more accurately
the device temperature, new thermal resistance specifications
have been developed. Unlike older regulators with a single
junction-to-case thermal resistance specification, the data section
for these new regulators provides a separate thermal resistance
and maximum junction temperature for both the Control Section
and the Power Transistor. Calculations for both temperatures
under certain conditions of ambient temperature and heat sink
resistance and to ensure that both thermal limits are met.
Junction-to-case thermal resistance is specified from the IC
junction to the bottom of the case directly below the die. This is
the lowest resistance path for the heat flow. In order to ensure the
best possible thermal flow from this area of the package to the
heat sink proper mounting is required. Thermal compound at the
case-to-heat sink interface is recommended. A thermally
conductive spacer can be used, if the case of the device must be
electrically isolated, but its added contribution to thermal
resistance has to be considered.
P is
not multiplied by the divider ratio.
AMS1084