LT3080EDD-1 LINER [Linear Technology], LT3080EDD-1 Datasheet - Page 13

• Manufacturer Part Number: LT3080EDD-1
• Description: Parallelable 1.1A Adjustable Single Resistor Low Dropout Regulator
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
Load Regulation
Because the LT3080-1 is a fl oating device (there is no
ground pin on the part, all quiescent and drive current is
delivered to the load), it is not possible to provide true
remote load sensing. Load regulation will be limited by the
resistance of the connections between the regulator and
the load. The data sheet specifi cation for load regulation
is Kelvin sensed at the pins of the package. Negative side
sensing is a true Kelvin connection, with the bottom of
the voltage setting resistor returned to the negative side of
the load (see Figure 7). Connected as shown, system load
regulation will be the sum of the LT3080-1 load regulation
and the parasitic line resistance multiplied by the output
current. It is important to keep the positive connection
between the regulator and load as short as possible and
use large wire or PC board traces.
The internal 25mΩ ballast resistor is outside of the
LT3080-1’s feedback loop. Therefore, the voltage drop
across the ballast resistor appears as additional DC load
regulation. However, this additional load regulation can
actually improve transient response performance by
decreasing peak-to-peak output voltage deviation and
even save on total output capacitance. This technique is
called active voltage positioning and is especially useful for
applications that must withstand large output load current
transients. For more information, see Design Note 224,
“Active Voltage Positioning Reduces Output Capacitors.”
The basic principle uses the fact that output voltage is a
V
CONTROL
Figure 7. Connections for Best Load Regulation
IN
SET R
+
–
LT3080-1
SET
25mΩ
function of output load current. Output voltage is set based
on the midpoint of the output load current range:
As output current decreases below the midpoint, output
voltage increases above the nominal set-point. Corre-
spondingly, as output current increases above the midpoint,
output voltage decreases below the nominal set-point.
During a large output load transient, output voltage
perturbation is contained within a window that is tighter
than what would result if active voltage positioning is not
employed. Choose the SET pin resistor value by using the
formula below:
where
I
R
I
Thermal Considerations
The LT3080-1 has internal power and thermal limiting
circuitry designed to protect it under overload conditions.
For continuous normal load conditions, maximum junction
temperature must not be exceeded. It is important to
MID
SET
BALLAST
R
2
1
= 10μA
SET
= 1/2 (I
OUT
•
(
RESISTANCE
I
PARASITIC
OUT MIN
=
= 25mΩ
R
R
R
(
P
P
P
OUT(MIN)
(
V
OUT
LOAD
)
30801 F07
+
+
I
I
OUT MAX
MID
+ I
I
SET
OUT(MAX)
(
•
R
BALLAST
)
)
)
)
LT3080-1
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