LT1937
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Switching Frequency
Quiescent Current
SHDN Pin Bias Current
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
400
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
–50°C
350
300
100°C
25°C
SHDN = 10V
250
200
150
100
50
SHDN = 3.6V
SHDN = 2.7V
SHDN = 3V
0
0
2
4
6
8
10
–25
0
50
75
100
50
TEMPERATURE (°C)
100
–50
25
–50
–25
0
25
75
V
IN
(V)
TEMPERATURE (°C)
1937 G01
1937 G02
1937 G03
Feedback Bias Current
Efficiency vs Temperature
Current Limit vs Duty Cycle
350
300
250
200
150
100
50
60
50
40
30
85
V
= 3.6V
IN
3 LEDs
I
= 20mA
LED
84
83
82
81
80
I
I
= 15mA
= 10mA
LED
LED
20
10
0
0
20
40
DUTY CYCLE (%)
80
100
0
60
50
100
–50
–25
0
25
75
–50
0
50
TEMPERATURE (°C)
100
TEMPERATURE (°C)
1937 G06
1937 G04
1937 G05
U
U
U
PI FU CTIO S
SW (Pin 1): Switch Pin. Connect inductor/diode here.
Minimize trace area at this pin to reduce EMI.
SHDN (Pin 4):Shutdown Pin. Connect to 1.5Vor higher to
enable device; 0.4V or less to disable device.
GND (Pin 2): Ground Pin. Connect directly to local ground
plane.
GND (Pin 5, SC70 Package): Ground Pin. Connect to Pin
2 and 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:
VIN (Pin 5/Pin 6 SC70 Package): Input Supply Pin. Must
be locally bypassed.
RFB = 95mV/ILED
1937f
3
Linear [ Linear ]
