LT3080EDD-1 datasheet(13/24 Pages) LINER

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LT3080-1

30801fa

function of output load current. Output voltage is set based

on the midpoint of the output load current range:

•

()

(

)

OUT MIN

OUT MAX

()

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:

SET

OUT

MID

BALLAST

SET

(•

)

where

IMID = 1/2 (IOUT(MIN) + IOUT(MAX))

RBALLAST = 25mΩ

ISET = 10μA

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

Figure 7. Connections for Best Load Regulation

–

LT3080-1

VCONTROL

OUT

30801 F07

SET RSET

25mΩ

PARASITIC

RESISTANCE

LOAD

Load Regulation

Because the LT3080-1 is a ﬂoating 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 speciﬁcation 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

APPLICATIONS INFORMATION

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