DC928A - Demo Manual

DEMO CIRCUIT 928
LTC3452EUF
QUICK START
GUIDE
LTC3452EUF
SYNCHRONOUS BUCK-BOOST
MAIN/CAMERA WHITE LED DRIVER
DESCRIPTION
WARNING!
Do not look directly at operating LED.
This circuit produces light that can damage eyes.
Demonstration circuit 928 is a SYNCHRONOUS
BUCK-BOOST MAIN/CAMERA WHITE LED
DRIVER featuring the LTC3452EUF.
The backlight outputs (LEDL1-5) are activated by
depressing The ‘DISPLAY’ momentary switch,
or connecting the ‘ENL’ terminal to ‘VIN ’ with a
jumper wire. The backlight intensity can be
modulated by applying a 10kHz pwm signal to
the ‘ENL’ terminal, as indicated in the table.
Figure 2 shows efficiency at 200mA flash output
with various 4.7uH inductors.
The circuit drives two banks of LEDs: one
250mA flash device, and a bank of 5 LEDs at
20mA each for backlighting. The backlight LED
currents are typically matched within 2%. The
input voltage range of 2.7V to 5.5V is suitable
for a single Lithium-Ion battery or three AAA
batteries in series. Some of the many features
include: Lithium-Ion battery input voltage range,
flash LED output, separate, dimmable backlight
outputs, internal synchronous power switches,
minimal and low-profile external components,
and simple design; therefore the LTC3452 is the
top solution for highly efficient, spaceconstrained, cellular telephone camera flash solutions.
The LTC3452 datasheet gives a complete description of the part along with operation and
applications information. The datasheet must be
read in conjunction with this Quick Start Guide
for demonstration circuit 928. In addition, the
Nichia NSCW100 datasheet (www.nichia.com)
and the AOT2015 datasheet (www.aot.com)
must be read to understand thermal and LED
current constraints for varying flash current
pulse-widths and intensity. The LTC3452 is offered in a small low profile QFN package.
Proper board layout is essential for maximum
thermal performance. See the datasheet section
‘Layout Considerations’.
The flash output (LEDH) is activated by depressing The ‘FLASH’ momentary switch, or connecting the ‘ENH’ terminal to ‘VIN’ with a jumper
wire.
Design files for this circuit board are available.
Call the LTC factory.
WARNING- The LEDH LED can be permanently
damaged if the flash mode is engaged for more
than a few seconds.
, LTC, LTM, LT, Burst Mode, OPTI-LOOP, Over-The-Top and PolyPhase are
registered trademarks of Linear Technology Corporation. Adaptive Power, C-Load,
DirectSense, Easy Drive, FilterCAD, Hot Swap, LinearView, µModule, Micropower
SwitcherCAD, Multimode Dimming, No Latency , No Latency Delta-Sigma, No
RSENSE, Operational Filter, PanelProtect, PowerPath, PowerSOT, SmartStart,
SoftSpan, Stage Shedding, SwitcherCAD, ThinSOT, UltraFast and VLDO are
trademarks of Linear Technology Corporation. Other product names may be trademarks of the companies that manufacture the products.
1
LTC3452EUF
PERFORMANCE SUMMARY
SYMBOL
VIN
VOUT
IOUT
IOUT
VOUT P-P
IREG
FSW
POUT/PIN
PARAMETER
Input Supply Range
Output Voltage Range
Output Current – LEDH
Output Current – LEDL1 through LEDL5
Output Ripple
Output Regulation
Switching Frequency
Efficiency
Specifications are at TA = 25°C
CONDITIONS
MIN
2.7
VIN = 2.7V to 5.5V
VIN = 2.7V to 5.5V
VIN = 4.2V, IOUT = 20mA (20MHz BW)
Line, VIN = 2.7V to 5.5V
VIN = 4.2V, IOUT = 200mA
TYP
250
20
10
±1.0
1.0
85
MAX
5.5
4.4
UNITS
V
V
mA
mA each
mVP–P
%
MHz
%
QUICK START PROCEDURE
Demonstration circuit 928 is easy to set up to
evaluate the performance of the LTC3452EUF. Refer to Figure1 for proper measurement equipment
setup and follow the procedure below:
NOTE. When measuring output voltage ripple, care must be taken
to avoid a long ground lead on the oscilloscope probe. Measure the
output voltage ripple by touching the probe tip directly across the
output capacitor. See Figure 2 for proper scope probe technique.
4. Press ‘DISPLAY’ to observe a constant 20mA x
5 LED backlight for displays.
5. Press ‘FLASH’ to observe a 250mA camera
flash.
WARNING- The LEDH LED can be permanently
damaged if the flash mode is engaged for more
than a few seconds.
1. Preset a dc source capable of 5.5V at 1A to 4V.
2. With power off, connect the input power supply
to ‘VIN’ and ‘GND’ of the circuit.
3. Turn on the power at the input. The input voltage
may be varied between 2.7V and 5.5VDC .
NOTE. Make sure that the input voltage does not exceed 5.5V.
2
6. Alternatively, the backlight and flash modes can
be enabled by connecting ‘ENL’ (backlight), or
‘ENH’ (flash) to ‘VIN’.
7. The backlight intensity can be modulated by applying a 10kHz, 2V pwm signal to the ‘ENL’ terminal. Output current will vary with duty cycle,
as indicated in the table on the board.
LTC3452EUF
Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Input or Output Ripple
3
LTC3452EUF
Efficiency vs Vin, Io = 200mA
90
Efficiency, %
87.5
Coilcraft DO3314
Vishay IDCS2512
Wurth 744031004
Coiltronics SD3814
Coiltronics SD14
Coiltronics SD18
Coiltronics SD20
Coiltronics SD25
85
82.5
80
2.7
3.1
3.5
3.9
4.3
4.7
Vin, V
Figure 3. Efficiency
4
5.1
5.5
LTC3452EUF
5
Similar pages