LT3021 datasheet(11/20 Pages) LINER

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LT3008 Series

3008fc

PIN FUNCTIONS

SHDN (Pin 1/Pin 5): Shutdown. Pulling the SHDN pin

low puts the LT3008 into a low power state and turns the

output off. If unused, tie the SHDN pin to VIN. The LT3008

does not function if the SHDN pin is not connected. The

SHDN pin cannot be driven below GND unless tied to the

IN pin. If the SHDN pin is driven below GND while IN is

powered, the output will turn on. SHDN pin logic cannot

be referenced to a negative rail.

GND (Pins 2, 3, 4/Pin 6): Ground. Connect the bottom

of the resistor divider that sets output voltage directly to

GND for the best regulation.

IN (Pin 5/Pin 4): Input. The IN pin supplies power to the

device. The LT3008 requires a bypass capacitor at IN if

the device is more than six inches away from the main

input ﬁlter capacitor. In general, the output impedance of

a battery rises with frequency, so it is advisable to include

a bypass capacitor in battery-powered circuits. A bypass

capacitor in the range of 0.1μF to 10μF will sufﬁce. The

LT3008 withstands reverse voltages on the IN pin with

respect to ground and the OUT pin. In the case of a reversed

input, which occurs with a battery plugged in backwards,

the LT3008 acts as if a blocking diode is in series with its

input. No reverse current ﬂows into the LT3008 and no

reverse voltage appears at the load. The device protects

both itself and the load.

OUT (Pin 6/Pins 2, 3): Output. This pin supplies power

to the load. Use a minimum output capacitor of 2.2μF

to prevent oscillations. Large load transient applications

require larger output capacitors to limit peak voltage

transients. See the Applications Information section for

more information on output capacitance and reverse-output

characteristics.

ADJ (Pin 7/Pin 1): Adjust. This pin is the error ampliﬁer’s

inverting terminal. Its 400pA typical input bias current

ﬂows out of the pin (see curve of ADJ Pin Bias Current vs

Temperature in the Typical Performance Characteristics

section). The ADJ pin voltage is 600mV referenced to GND

and the output voltage range is 600mV to 44.5V.

NC (Pin 8, TSOT-23 Package Only): No Connect. Pin 8

is an NC pin in the TSOT-23 package. This pin is not tied

to any internal circuitry. It may be ﬂoated, tied to VIN or

tied to GND.

GND (Exposed Pad Pin 7, DFN Package Only): Ground. The

exposed pad (backside) of the DFN package is an electrical

connection to GND. To ensure optimum performance,

solder Pin 7 to the PCB and tie directly to Pin 6.

SENSE (Pin 7/Pin 1): Sense. For ﬁxed voltage versions of

the LT3008 (LT3008-1.2, LT3008-1.5, LT3008-1.8, LT3008-

2.5, LT3008-3.3, LT3008-5), the SENSE pin is the input to

the error ampliﬁer. Optimum regulation is obtained at the

point where the SENSE pin is connected to the OUT pin of

the regulator. In critical applications, small voltage drops

are caused by the resistance (RP) of PC traces between

the regulator and the load. These may be eliminated by

connecting the SENSE pin to the output at the load as

shown in Figure 1 (Kelvin Sense Connection). Note that

the voltage drop across the external PC traces add to the

dropout voltage of the regulator. The SENSE pin bias current

is 1μA at the nominal rated output voltage. The SENSE pin

can be pulled below ground (as in a dual supply system

where the regulator load is returned to a negative supply)

and still allow the device to start and operate.

(TSOT-23/DFN)

SHDN

3008 F01

OUT

VIN

SENSE

GND

LT3008

LOAD

Figure 1. Kelvin Sense Connection

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