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
