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LT3082

200mA Single Resistor Low Dropout Linear Regulator

Linear Technology 

LT3082

APPLICATIONS INFORMATION

Table 1. 1% Resistors for Common Output Voltages

VOUT (V)

1

RSET (k)

100

1.2

121

1.5

150

1.8

182

2.5

249

3.3

332

5

499

With a 10μA current source generating the reference

voltage, leakage paths to or from the SET pin can create

errors in the reference and output voltages. High qual-

ity insulation should be used (e.g., Teflon, Kel-F). The

cleaning of all insulating surfaces to remove fluxes and

other residues may be required. Surface coating may be

necessary to provide a moisture barrier in high humidity

environments.

Minimize board leakage by encircling the SET pin and

circuitry with a guard ring that is operated at a potential

close to itself. Tie the guard ring to the OUT pin. Guarding

both sides of the circuit board is required. Bulk leakage

reduction depends on the guard ring width. 10nA of leak-

age into or out of the SET pin and its associated circuitry

creates a 0.1% reference voltage error. Leakages of this

magnitude, coupled with other sources of leakage, can

cause significant offset voltage and reference drift, es-

pecially over the possible operating temperature range.

Figure 2 depicts an example guard ring layout.

If guard ring techniques are used, this bootstraps any

stray capacitance at the SET pin. Since the SET pin is

a high impedance node, unwanted signals may couple

into the SET pin and cause erratic behavior. This will

be most noticeable when operating with minimum

output capacitors at full load current. The easiest way

to remedy this is to bypass the SET pin with a small

amount of capacitance from SET to ground; 10pF to

20pF is sufficient.

Stability and Output Capacitance

The LT3082 requires an output capacitor for stability. It

is designed to be stable with most low ESR capacitors

(typically ceramic, tantalum or low ESR electrolytic). A

minimum output capacitor of 2.2μF with an ESR of 0.5Ω

or less is recommended to prevent oscillations. Larger

values of output capacitance decrease peak deviations

and provide improved transient response for larger load

current changes. Bypass capacitors, used to decouple

individual components powered by the LT3082, increase

the effective output capacitor value. For improvement in

transient response performance, place a capacitor across

the voltage setting resistor. Capacitors up to 1μF can be

used. This bypass capacitor reduces system noise as well,

but start-up time is proportional to the time constant of

the voltage setting resistor (RSET in Figure 1) and SET pin

bypass capacitor.

Give extra consideration to the use of ceramic capacitors.

Ceramic capacitors are manufactured with a variety of di-

OUT

SET

GND

3082 F02

Figure 2. Example Guard Ring Layout for DFN Package

3082f

9

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