QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 484
SINGLE CELL WHITE LED DRIVER
LT1937
DESCRIPTION
Demonstration circuit 484 features the LT1937 constant-
current white LED driver in a small SOT23 ThinSOT
package. The demo board is designed to demonstrate
the high efficiency performance and the small size of the
LT1937. The LT1937 features a 95mV feedback voltage,
1.2MHz switching frequency and a special internal com-
pensation network, which allows small (0603) input and
output capacitors. DC484 is specifically designed for
white LED backlight applications using 2–4 LEDs, mak-
ing LT1937-SOT23 an ideal solution for battery powered
portable applications such as cellular phones, digital
cameras, MP3 players, GPS receivers, and handheld
computers (PDAs). LT1937 offers numerous LED dim-
ming circuit options, see the datasheet for details.
Design files for this circuit board are available from
the LTC factory.
QUICK START PROCEDURE
Demonstration circuit 484 is easy to set up to evaluate
the performance of the LT1937. Refer to Figure 1 for
proper measurement equipment setup and follow the
procedure below:
NOTE:
When measuring the input or output voltage rip-
ple, care must be taken to avoid a long ground lead on
the oscilloscope probe. Measure the input or output
voltage ripple by touching the probe tip directly across
the Vin or Vout and GND terminals. See Figure 2 for
proper scope probe technique.
1.
The demo board can be powered from a 3V Lithium
battery installed on the demo board (B1) or other in-
put source (bench top power supply) by selecting in-
put source jumper (JP1).
For battery (B1) input operation, place the jumper
(JP1) to the “BATTERY” position.
For bench supply input, place the jumper (JP1) in the
Vin position and connect a 3.3V, 500mA Bench supply
to the Vin and GND terminals.
2.
Turn on the input power supply or connect the single
cell Li-Ion battery. Turn on the LT1937 LED driver cir-
cuit by pushing down SW1. Observe all four white
LEDs light up. The output voltage should measure
about 13V across the Vout Test terminal to GND ter-
minal.
3.
The brightness of the LEDs can be controlled by ap-
plying a PWM signal to the SHDN terminal. The typi-
cal frequency range recommended for PWM dimming
is 1KHz–10KHz with the signal magnitude of the PWM
signal higher than 1.5V. See the LT1937 data sheet for
more information about PWM dimming control.
OPTIONAL SUPPLY TO
ON-BOARD BATTERY
OPTIONAL
DIMMING
CONTROL VIA
1KHz-10KHz
PWM SIGNAL
(>1.5V)
SEE LT1937
DATASHEET
FOR DETAILS
+
–
+
–
+
–
+
–
VIN
GND
Figure 1.
Proper Measurement Equipment Setup Figure 2.
Measuring Ripple
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 484
SINGLE CELL WHITE LED DRIVER
2.7V - 5 V
Vou t Test
Vi n
BATTERY
12mA
GND GND
BATTERY
VIN
SHDN
WHITE
ON/OFF
L1
22uH
LED4
LED1
LED2
E3
E4
D1
CMDSH-3
C1
1uF
6.3V
B1
+
R2
100 K
E5
LED3
R1
7. 5
1%
JP1
1
2
3
E1
U1
LT1937E S5
5 1
3
2
4
Vin SW
FB
GND
SHDN
SW1
E2
C2
0. 22uF
16V
Figure 3.
Schematic
2
5
5
4
4
3
3
2
2
1
1
D D
C C
B B
A A
2.7V - 5V
Vout Test
Vin
BATTERY
12mA
GND GND
BATTERY
VIN
SHDN
WHITE
ON/OFF
A
DEMO DC484A
Friday, December 14, 2001
11
LT1937ES5, SINGLE CELL WHITE LED DRIVER
June Wu 11/27/01
David Chen 11/27/01
SIZE
SCALE:
CAGE CODE DWG NO REV
SHEET OF
FILENAME:
TITLE
CONTRACT NO.
APPROVALSDATE
DRAWN
CHECKED
APPROVED
ENGINEER
DESIGNER
TECHNOLOGY
1630 McCarthy Blvd.
Milpitas, CA 95035
Phone: (408)432-1900
Fax: (408)434-0507
L1
22uH
LED4
LED1
LED2
E3
E4
D1
CMDSH-3
C1
1uF
6.3V
B1
+
R2
100K
E5
LED3
R1
7.5
1%
JP1
1
2
3
E1
U1
LT1937ES5
5 1
3
2
4
Vin SW
FB
GND
SHDN
SW1
E2
C2
0.22uF
16V
Linear Technology Corporation
LT1937ES5
Bill Of Material
Demo Bd. #484A
6/17/2005
12:34 PM
Item Qty Reference Part Description Manufacture / Part #
1 1 B1 BATTERY, AA SANYO., CR2
2 2 B1 HOLDER BATTERY HOLDER, KEYSTONE, 92
3 1 L1 INDUCTOR, 22uH MURATA, LQH32CN220K51L
4 1 C1 CAP., X5R, 1.0uF, 6.3V, 20% 0603 TAIYO YUDEN, JMK107BJ105MA
5 1 C2 CAP., X7R, 0.22uF, 16V 20% 0805 TAIYO YUDEN, EMK212BJ224MG
6 1 D1 DIODE, CMDSH-3, SOD-323 Central Semi. CMDSH-3
7 5 E1,E2,E3,E4,E5 TESTPOINT, TURRET, .094" MILL-MAX, 2501-2
8 1 JP1 JUMPER, 0.079, 3 PIN COMM CON, 2802S-03G1
9 1 JP1 (BATTERY SIDE) SHUNT, COMM CON. CCIJ2MM-138G
10 4 LED1-LED4 LED, NSCX SERIES, WHITE NICHIA, NSCW100
11 1 R1 RES., CHIP, 7.5, 1/16W, 1% 0402 AAC., CR05-7R50FM
12 1 R2 RES., CHIP, 100K, 1/16W, 5% 0402 AAC., CR05-104JM
13 1 SW1 SWITCH MOMENTARY PANASONIC EVQ PJS 05K
14 1 U1 IC., LT1937, SOT23-S5 LINEAR., LT1937ES5 (Bulk)
15 1 PRINTED CIRCUIT BOARD DEMO BOARD DC484A
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