QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 507
SINGLE CELL WHITE LED DRIVER
LT1937
DESCRIPTION
Demonstration circuit 507 features the LT1937 constant-
current white LED driver in a small SC70 package. The
demo board consists of two circuits: an efficiency circuit
designed to demonstrate high efficiency performance of
the LT1937 using the Murata inductor and a size circuit
highlighting the LT1937’s ability to work with a small
ceramic chip inductor and a small output capacitor
(0.22µF). The high efficiency and small circuit size are
made possible by a 95mV feedback voltage and 1.2MHz
switching frequency, making the LT1937-SC70 an ideal
solution for battery powered portable applications such
as cellular phones, digital cameras, MP3 players, GPS
receivers, and handheld computers (PDAs). The DC507
is specifically designed for white LED backlight applica-
tions using 2–4 LEDs in series. LT1937 offers numerous
LED-dimming circuit options, see the datasheet for more
detailed information on LED brightness control.
Design files for this circuit board are available. Call
the LTC factory.
QUICK START PROCEDURE
Demonstration circuit 507 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. When measuring the
output ripple, see Figure 2 for proper scope probe tech-
nique.
SET THE INPUT VOLTAGE SOURCE
1.
The demo board can be powered from the 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).
a.
For battery (B1) input operation, place the jumper
(JP1) in the BATTERY position.
b.
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.
TEST THE EFFICIENCY CIRCUIT (UPPER CIRCUIT)
2.
Place jumper JP2 in the EFFICIENCY position.
3.
Press the SW1 switch. Observe all four white LEDs
light up. The output voltage should measure about
13V across the Vout Test terminal to GND terminal.
4.
Turn off the input power supply or disconnect the sin-
gle cell Li-Ion battery.
TEST THE SIZE CIRCUIT (LOWER CIRCUIT)
5.
Place jumper JP2 in the SIZE position.
6.
Turn on the input power supply or connect the single
cell Li-Ion battery.
7.
Press the SW2 switch. Observe all four white LEDs
light up. The output voltage should measure about
13V across the Vout Test terminal to GND terminal.
LED BRIGHTNESS CONTROL
The brightness of the LEDs can be controlled by apply-
ing a PWM signal to the SHDN terminal (use the upper
SHDN terminal for the EFFICIENCY circuit and lower
SHDN terminal for the SIZE circuit). The typical fre-
quency range recommended for PWM dimming is
1KHz–10KHz with the signal magnitude of the PWM sig-
nal higher than 1.5V. See the LT1937 data sheet for more
information on PWM dimming control.
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 507
SINGLE CELL WHITE LED DRIVER
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–
+
–
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–
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Figure 1.
Proper Measurement Equipment Setup
VIN
GND
Figure 2.
Scope Probe Placement for Measuring Input or Output Ripple
2
5
5
4
4
3
3
2
2
1
1
D D
C C
B B
A A
Vin
GND
BATTERY
ON/OFF
BATTERY
SHDN
Vout Test
12mA
VIN
2.7V - 5V
GND
WHITE
SIZE
EFFICIENCY
SHDN
ON/OFF
A
DC507A
Thursday, March 21, 2002
11
LT1937ESC6, SINGLE CELL WHITE LED DRIVER
June Wu 2/13/02
DAVE KIM 2/13/02
SIZE
SCALE:
CAGE CODE DWG NO REV
SHEET OF
FILENAME:
TITLE
CONTRACT NO.
APPROVALS DATE
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
L2
22uH
E6
SW2
C4
2.2uF
6.3V
E3
E4
D1
CMDSH-3
D2
CMDSH-3
C3
0.47uF
16V
JP2
1
2
3
C1
2.2uF
6.3V
B1
+
R2
100K
E5
R3
100K
LED3
R1
8.06
1%
E1
JP1
1
2
3
U2
LT1937ESC6
6 1
3
2
4
5
Vin SW
FB
GND
SHDN
GND
SW1
E2
C2
0.47uF
16V
U1
LT1937ESC6
6 1
3
2
4
5
Vin SW
FB
GND
SHDN
GND
Linear Technology Corporation
LT1937ESC6
Bill Of Material
Demo Bd. #507A
6/17/2005
Item Qty Reference Part Description Manufacture / Part #
1 0 B1 BATTERY, AA SANYO., CR2,
2 2 B1 HOLDER BATTERY HOLDER, KEYSTONE, 92
3 1 L1 INDUCTOR, 22uH MURATA, LQH32CN220K51
4 1 L2 INDUCTOR, 22uH TAIYO YUDEN, LB2012T220M
5 2 C1,C4 CAP., X5R, 2.2uF, 6.3V, 20% 0603 AVX, 06036D225MAT
6 2 C2,C3 CAP., X5R, 0.47uF, 16V 20% 0603 AVX, 0603YD474MAT
7 2 D1,D2 DIODE, CMDSH-3, SOD-323 Central Semi. CMDSH-3
8 6 E1,E2,E3,E4,E5,E6 TESTPOINT, TURRET, .094" MILL-MAX, 2501-2
9 2 JP1,JP2 JUMPER, 0.079, 3 PIN COMM CON, 2802S-03G1
10 2 JP1,JP2 SHUNT, COMM CON. CCIJ2MM-138G
11 4 LED1-LED4 LED, NSCX SERIES, WHITE NICHIA, NSCW100
12 1 R1 RES., CHIP, 8.06, 1/16W, 1% 0402 AAC., CR05-8R06FM
13 2 R2,R3 RES., CHIP, 100K, 1/16W, 5% 0402 AAC., CR05-104JM
14 2 SW1,SW2 SWITCH MOMENTARY PANASONIC EVQ PJS 05K
15 2 U1,U2 IC., LT1937ESC6, SC70 LINEAR., LT1937ESC6
16 1 PRINTED CIRCUIT BOARD DEMO CIRCUIT 507A
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