LT1937
TYPICAL PERFOR A CE CHARACTERISTICS
Quiescent Current
2.2
2.0
1.8
1.6
1.4
25°C
100°C
–50°C
SHDN PIN BIAS CURRENT (µA)
300
SHDN = 10V
250
200
150
100
50
SHDN = 3.6V
SHDN = 3V
SWITCHING FREQUENCY (MHz)
I
Q
(mA)
1.2
1.0
0.8
0.6
0.4
0.2
0
0
2
4
V
IN
(V)
1937 G01
6
Feedback Bias Current
60
FEEDBACK BIAS CURRENT (nA)
50
CURRENT LIMIT (mA)
EFFICIENCY (%)
40
30
20
10
0
–50
–25
50
25
0
TEMPERATURE (°C)
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:
R
FB
= 95mV/I
LED
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
V
IN
(Pin 5/Pin 6 SC70 Package):
Input Supply Pin. Must
be locally bypassed.
U W
8
75
1937 G04
SHDN Pin Bias Current
400
350
1.4
1.2
1.0
0.8
0.6
0.4
0.2
Switching Frequency
SHDN = 2.7V
– 25
50
25
TEMPERATURE (°C)
0
75
100
1937 G02
10
0
– 50
0
–50
–25
50
25
0
TEMPERATURE (°C)
75
100
1937 G03
Efficiency vs Temperature
85
V
IN
= 3.6V
3 LEDs
350
Current Limit vs Duty Cycle
300
250
200
150
100
50
0
84
I
LED
= 20mA
83
I
LED
= 15mA
82
I
LED
= 10mA
81
100
80
–50
50
0
TEMPERATURE (°C)
100
1937 G05
0
20
40
60
DUTY CYCLE (%)
80
100
1937 G06
U
U
U
1937f
3
LINER [ LINEAR TECHNOLOGY ]
