LT3085 datasheet(7/28 Pages) LINER

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LT3085

3085fb

TYPICAL PERFORMANCE CHARACTERISTICS

Error Ampliﬁer Gain and Phase

FREQUENCY (Hz)

100k

3085 G28

–3

–6

–9

–72

216

–216

–360

–144

144

–288

–432

–504

100

10k

ILOAD = 500mA

ILOAD = 100mA

ILOAD = 500mA

Ripple Rejection - SET Pin Current

FREQUENCY (Hz)

150

10k

100k

100

3085 G29

120

135

105

CSET = 0.1μF

CSET = 0

RSET = 100k

VIN = VCONTROL = VOUT (NOMINAL) +2V

RIPPLE = 50mVP–P

PIN FUNCTIONS

VCONTROL (Pin 4/Pin 5): This pin is the supply pin for the

control circuitry of the device. The current ﬂow into this

pin is about 1.7% of the output current. For the device to

regulate, this voltage must be more than 1.2V to 1.35V

greater than the output voltage (see VCONTROL Dropout

Voltage in the Electrical Characteristics table and graphs

in the Typical Performance Characteristics). The LT3085

requires a bypass capacitor at VCONTROL if more than six

inches away from the main input ﬁlter capacitor. The output

impedance of a battery rises with frequency, so include

a bypass capacitor in battery-powered circuits. A bypass

capacitor in the range of 1μF to 10μF sufﬁces.

IN (Pins 5, 6/Pins 7, 8): This is the collector to the power

device of the LT3085. The output load current is supplied

through this pin. For the device to regulate, the voltage at

this pin must be more than 0.1V to 0.5V greater than the

output voltage (see VIN Dropout Voltage in the Electrical

Characteristics table and graphs in the Typical Perfor-

mance Characteristics). The LT3085 requires a bypass

capacitor at IN if more than six inches away from the main

input ﬁlter capacitor. The output impedance of a battery

rises with frequency, so include a bypass capacitor in

battery-powered circuits. A bypass capacitor in the range

of 1μF to 10μF sufﬁces.

NC (NA/Pin 6): No Connection. The No Connect pin has

no connection to internal circuitry and may be tied to VIN,

VCONTROL, VOUT, GND, or ﬂoated.

OUT (Pins 1, 2/Pins 1, 2, 3): This is the power output

of the device. There must be a minimum load current of

1mA or the output may not regulate. A minimum 2.2μF

output capacitor is required for stability.

SET (Pin 3/Pin 4): This pin is the non-inverting input to the

error ampliﬁer and the regulation set point for the device.

A ﬁxed current of 10μA ﬂows out of this pin through a

single external resistor, which programs the output voltage

of the device. Output voltage range is zero to the absolute

maximum rated output voltage. Transient performance can

be improved and output noise can be decreased by adding

a small capacitor from the SET pin to ground.

Exposed Pad (Pin 7/Pin 9): OUT. Tie directly to Pins 1, 2/

Pins 2, 3 directly at the PCB.

(DCB/MS8E)

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