LT1963 datasheet(9/28 Pages) LINER

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LT3089

3089f

For more information www.linear.com/LT3089

BLOCK DIAGRAM

–

50µA

IMON

TEMPERATURE

DEPENDENT

CURRENT SOURCE

1µA/°C

SET

ILIM

OUT 3089 BD

PROGRAMMABLE

CURRENT LIMIT

CURRENT

MONITOR

IMON = ILOAD/5000

TEMP

PIN FUNCTIONS

IN: Input. This pin supplies power to regulate internal

circuitry and supply output load current. For the device

to operate properly and regulate, the voltage on this pin

must be between the dropout voltage and 36V above the

OUT pin (depending on output load current, see Dropout

Voltage Specifications).

OUT: Output. This is the power output of the device. The

LT3089 requires a 3mA minimum load current for proper

output regulation.

TEMP: Temperature Output. This pin delivers a current

proportional to the internal average junction temperature.

Current output is 1µA/°C for temperatures above 5°C. The

TEMP pin output current typically equals 25µA at 25°C.

The output of the TEMP pin is valid for voltages from VOUT

+ 0.4V to VOUT – 40V. If unused, connect this pin to OUT.

ILIM: Current Limit Program. A resistor between this pin

and OUT programs output current limit to a level propor-

tional to resistor value. Connect this resistor directly to

OUT at the pins of the package. The typical ratio of current

limit to resistor value is 175mA/kΩ with a 300Ω offset.

If programmable current limit is not used, leave this pin

open; the internal current limit of the LT3089 is still active,

keeping the device inside safe operating limits. External

voltage drops between the current limit resistor and VOUT

will affect the current limit. Keep drops below 1mV.

IMON: Output Current Monitor. The IMON pin sources a

current typically equal to ILOAD/5000 or 200µA per amp of

output current. Terminating this pin with a resistor to GND

produces a voltage proportional to ILOAD. For example,

at ILOAD = 800mA, IMON typically sources 160µA. With

a 1k resistor to GND, this produces 160mV. The output

of the IMON pin is valid for voltages from VOUT + 0.4V to

VOUT – 40V. If unused, connect this pin to OUT.

SET: Set. This pin is the error amplifier’s noninverting

input and also sets the operating bias point of the circuit.

A fixed 50μA current source flows out of this pin. A single

external resistor programs VOUT. Output voltage range is

0V to 34.5V.

Exposed Pad/Tab: Output. The exposed pad of the DF

and FE packages and the tab of the R package are tied

internally to OUT. As such, tie them directly to OUT (Pins

1-4/Pins 1-5, 8, 9, 16/Pin 4) at the PCB. The amount of

copper area and planes connected to OUT determine the

effective thermal resistance of the packages.

NC: No Connection. No connect pins have no connection

to internal circuitry and may be tied to IN, OUT, GND or

floated.

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