Analog Devices DC336 User manual

DC336 QUICK START GUIDE
Description
Demonstration circuit DC336 is a white LED driver using the LTC3200 low noise, constant
frequency, inductorless DC/DC converter. The circuit is designed to drive five white LEDs from
a single Li-Ion cell. The LTC3200’s 2MHz constant switching frequency and internal switching
control result in extremely low input and output ripple and small circuit size (23mm2). DC336 is
specifically targeted for white LED backlight applications in cellular phones and small handheld
devices, such as PDAs, where noise and circuit size are critical. The input ripple and output
ripple performance can be improved by using 4.7µF, X7R ceramic capacitors at the input and
output (refer to the LTC3200 data sheet). Gerber files for this circuit board are available. Call the
LTC factory.
Quick Start
DC336 is easy to set up to evaluate the LTC3200 low noise, LED driver circuit. Refer to Figure 1
for equipment setup and follow the procedure outlined below:
1. Before turning on the power supply, connect a 3.3V, 500mA bench supply to the VIN and GND
terminals.
2. Turn on the input power supply and observe that the white LEDs light up. The output voltage
should measure 5V (typical) with 3V–4.2V input voltage.
3. Connect the JP1 jumper to the “off” position to turn off the LTC3200. Returning the jumper to
the “on” position will turn on the LTC3200.
+
–
+
–
VIN
GND
SHDN
VOUT
GND
JP1 ] OFF
] ON
LTC3200ES6
White LED Driver for Cellular Phone
Demo Circuit DC336A
POWER
SUPPLY
Figure 1. DC336A Test and Measurement Setup

4. When measuring the input / output voltage ripple, care must be taken to avoid a long ground
return for the oscilloscope probe. After removing the grabber and outer plastic sleeve from the
scope probe, measure the input voltage ripple by touching the probe between VIN and GND
and measure the output voltage ripple by touching the probe between VOUT and GND as
shown in Figure 2.
VIN
GND
VOUT
GND
MEASURING
V
IN
RIPPLE
MEASURING
V
OUT
RIPPLE
TEKTRONIX
TDS 640A
OSCILLOSCOPE
PROBE
Figure 2. Proper Noise Measurement Technique