3

LT1945

1945f

Quiescent Current

TYPICAL PERFOR A CE CHARACTERISTICS

Switch Saturation Voltage

FB2 Pin Voltage and

Bias Current

TEMPERATURE (

°C)

–50

–25

0

25

50

75

100

1945 G01

0.60

0.55

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

TEMPERATURE (

°C)

–50

1945 G02

1.25

1.24

1.23

1.22

1.21

1.20

50

40

30

20

10

0

CURRENT

VOLTAGE

–25

0

25

50

75

100

TEMPERATURE (

°C)

1945 G03

–1.25

–1.24

–1.23

–1.22

–1.21

–1.20

–50

–25

0

0

1

2

3

4

5

25

50

75

100

VOLTAGE

CURRENT

PI FU CTIO S

NFB1 (Pin 1): Feedback Pin for Switcher 1. Set the output

voltage by selecting values for R1 and R2.

SHDN1 (Pin 2): Shutdown Pin for Switcher 1. Tie this pin

to 0.9V or higher to enable device. Tie below 0.25V to turn

it off.

GND (Pin 3): Ground. Tie this pin directly to the local

ground plane.

SHDN2 (Pin 4): Shutdown Pin for Switcher 2. Tie this pin

to 0.9V or higher to enable device. Tie below 0.25V to turn

it off.

FB2 (Pin 5): Feedback Pin for Switcher 2. Set the output

voltage by selecting values for R1B and R2B.

SW2 (Pin 6): Switch Pin for Switcher 2. This is the

collector of the internal NPN power switch. Minimize the

metal trace area connected to the pin to minimize EMI.

PGND (Pins 7, 9): Power Ground. Tie these pins directly

to the local ground plane. Both pins must be tied.

capacitor as close to the device as possible.

SW1 (Pin 10): Switch Pin for Switcher 1. This is the

collector of the internal NPN power switch. Minimize the

metal trace area connected to the pin to minimize EMI.

TEMPERATURE (

°C)

1945 G04

550

500

450

400

350

300

250

–50

–25

0

25

50

75

100

TEMPERATURE (

°C)

1945 G05

400

350

300

250

200

150

100

50

0

–50

–25

0

25

50

75

100

Switch Off Time

Switch Current Limit

NFB1 Pin Voltage and

Bias Current

TEMPERATURE (

°C)

1945 G06

25

23

21

19

17

15

–50

–25

0

25

50

75

100

NOT SWITCHING