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-
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
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
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-
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.
OPTIONAL SUPPLY TO
ON-BOARD BATTERY
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
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
Linear Technology Corporation
LT1937ES5
Bill Of Material
Demo Bd. #484A
6/17/2005
12:34 PM
Item Qty Reference
Part Description
Manufacture / Part #
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
1
2
1
1
1
1
5
1
1
4
1
1
1
1
1
B1
B1 HOLDER
L1
C1
C2
D1
E1,E2,E3,E4,E5
JP1
JP1 (BATTERY SIDE)
LED1-LED4
R1
R2
SW1
U1
BATTERY, AA
BATTERY HOLDER,
INDUCTOR, 22uH
CAP., X5R, 1.0uF, 6.3V, 20% 0603
CAP., X7R, 0.22uF, 16V 20% 0805
DIODE, CMDSH-3, SOD-323
TESTPOINT, TURRET, .094"
JUMPER, 0.079, 3 PIN
SHUNT,
LED, NSCX SERIES, WHITE
RES., CHIP, 7.5, 1/16W, 1% 0402
RES., CHIP, 100K, 1/16W, 5% 0402
SWITCH MOMENTARY
IC., LT1937, SOT23-S5
PRINTED CIRCUIT BOARD
SANYO., CR2
KEYSTONE, 92
MURATA, LQH32CN220K51L
TAIYO YUDEN, JMK107BJ105MA
TAIYO YUDEN, EMK212BJ224MG
Central Semi. CMDSH-3
MILL-MAX, 2501-2
COMM CON, 2802S-03G1
COMM CON. CCIJ2MM-138G
NICHIA, NSCW100
AAC., CR05-7R50FM
AAC., CR05-104JM
PANASONIC EVQ PJS 05K
LINEAR., LT1937ES5 (Bulk)
DEMO BOARD DC484A
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