8

LT3021/LT3021-1.2/

LT3021-1.5/LT3021-1.8

3021fa

BLOCK DIAGRA

SHUTDOWN

–

+

CURRENT

GAIN

THERMAL

SHUTDOWN

R3

R2

R1

D1

Q1

D2

Q2

ERROR AMP

NO-LOAD

RECOVERY

Q3

IN

(12, 14/8)

OUT

(3,4/2)

OUT SENSE

(7/3)

NOTE:

FOR LT3021 ADJUST PIN (7/3) IS CONNECTED TO

THE ADJUST PIN, R1 AND R2 ARE EXTERNAL.

FOR LT3021-1.X PIN (7/3) IS CONNECTED TO THE

OUTPUT SENSE PIN, R1 AND R2 ARE INTERNAL.

GND

(8,10,17/4,6)

ADJ

(7/3)

SHDN

(9/5)

200mV

212mV

BIAS CURRENT

AND

REFERENCE

GENERATOR

FIXED

1.2V

1.5V

1.8V

R1

20k

20k

20k

R2

100k

130k

160k

25k

PI FU CTIO S

OUT (Pins 3, 4/Pin 2): These pins supply power to the load.

Use a minimum output capacitor of 3.3

µF to prevent oscil-

lations. Applications with large load transients require larger

output capacitors to limit peak voltage transients. See the

Applications Information section for more information on

output capacitance and reverse output characteristics.

SENSE (Pin 7/Pin 3, Fixed Voltage Device Only): This pin

is the sense point for the internal resistor divider. It should

be tied directly to the OUT pins (1, 2) for best results.

ADJ (Pin 7/Pin 3): This pin is the inverting terminal to the

error amplifier. Its typical input bias current of 20nA flows

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

Temperature in the Typical Performance Characteristics).

The ADJ pin reference voltage is 200mV (referred to GND).

AGND (Pin 8/Pin 4): Ground.

PGND (Pins 10, 17/Pin 6): Ground.

SHDN (Pin 9/Pin 5): The SHDN pin puts the LT3021 into

a low power state. Pulling the SHDN pin low turns the

output off. Drive the SHDN pin with either logic or an open

collector/drain device with a pull-up resistor. The pull-up

resistor supplies the pull-up current to the open collector/

drain logic, normally several microamperes, and the SHDN

pin current, typically 2.5

µA. If unused, connect the SHDN

is not connected.

IN (Pins 12, 14/Pin 8): These pins supply power to the

device. The LT3021 requires a bypass capacitor at IN if it

is more than six inches away from the main input filter

capacitor. The output impedance of a battery rises with fre-

quency, so include a bypass capacitor in battery-powered

circuits. A bypass capacitor in the range of 3.3

µF to 10µF

suffices. The LT3021 withstands reverse voltages on the

IN pin with respect to ground and the OUT pin. In the case

of a reversed input, which occurs if a battery is plugged in

backwards, the LT3021 acts as if a diode is in series with

its input. No reverse current flows into the LT3021 and no

reverse voltage appears at the load. The device protects itself

and the load.

EXPOSED PAD (Pin 17, DH16 Package Only): Ground.

Solder Pin 17 to the PCB ground. Connect directly to Pins

5, 8, 10 for best performance.

NC (Pins 1, 2, 5, 6, 11, 15, 16/Pins 1, 7)

(DH Package/S8 Package)

(DH Package/S8 Package)