3

LT1937

1937f

TYPICAL PERFOR A CE CHARACTERISTICS

Current Limit vs Duty Cycle

Quiescent Current

SHDN Pin Bias Current

Switching Frequency

Feedback Bias Current

PI FU CTIO S

SW (Pin 1): Switch Pin. Connect inductor/diode here.

Minimize trace area at this pin to reduce EMI.

GND (Pin 2): Ground Pin. Connect directly to local ground

plane.

FB (Pin 3): Feedback Pin. Reference voltage is 95mV.

Connect cathode of lowest LED and resistor here. Calcu-

late resistor value according to the formula:

SHDN (Pin 4): Shutdown Pin. Connect to 1.5V or higher to

enable device; 0.4V or less to disable device.

GND (Pin 5, SC70 Package): Ground Pin. Connect to Pin

2 and to local ground plane

be locally bypassed.

0

0

0.4

0.8

1.2

1.6

2468

1937 G01

10

2.0

0.2

0.6

1.0

1.4

1.8

2.2

–50

°C

100

°C

25

°C

TEMPERATURE (

°C)

–50

350

25

1937 G02

200

100

–25

0

50

50

0

400

300

250

150

75

100

SHDN = 10V

SHDN = 3.6V

SHDN = 3V

SHDN = 2.7V

TEMPERATURE (

°C)

–50

0.8

1.0

1.4

25

75

1937 G03

0.6

0.4

–25

0

50

100

0.2

0

1.2

TEMPERATURE (

°C)

–50

40

50

60

25

75

1937 G04

30

20

–25

0

50

100

10

0

Efficiency vs Temperature

TEMPERATURE (

°C)

–50

82

83

1937 G05

81

80

0

50

100

85

84

3 LEDs

DUTY CYCLE (%)

0

350

300

250

200

150

100

50

0

60

1937 G06

20

40

80

100