DC780A - Demo Manual

DEMO MANUAL DC780A
LT1618
Constant-Current 1.4MHz
White LED Driver
DESCRIPTION
Demonstration circuit 780A is a constant-current 1.4MHz
white LED driver featuring the LT®1618. The board is
optimized for 3.5V LED forward voltage output at 320mA
load current and a single lithium-ion input voltage range
of 3.3V to 4.2V. With its high frequency, constant-current
amplifier, internal power switch, low quiescent current,
1.4MHz switching frequency and thermally enhanced
package, the LT1618 is a very versatile and powerful IC
for driving 1W LEDs (such as a Luxeon LED, not installed)
that require either step-up and step-down capability from
lithium-ion supplies or step-up capability from 2-cell 1.8V
to 3.0V supplies used in very compact handheld solutions.
The LT1618 1.4MHz switching frequency allows all of
the components to be small, surface mount devices. The
current-mode control topology creates fast transient response and good loop stability with a minimum number
of external components. The constant-current amplifier
provides constant-current sensing without the need of an
PERFORMANCE SUMMARY
PARAMETER
external operational amplifier as used in other constantcurrent LED driver DC/DC converters.
The ON/OFF pushbutton is used to manually turn on the
LED. The BRIGHTNESS pushbutton is used to pulse the
LED in a brighter, higher current mode when the LED is
ON. The IADJ terminal can be used to program the LED
current. The VLED+ and VLED– terminals can be used to
monitor the LED forward voltage.
The LT1618 data sheet gives a complete description of the
part including operation and applications information. The
data sheet must be read in conjunction with this Quick
Start Guide for demonstration circuit 780A.
Design files for this circuit board are available at
http://www.linear.com/demo
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
(TA = 25°C)
CONDITION
Input Voltage Range
VALUE
3.3V to 4.2V
LED OFF Input Current
VIN = 3.6V, LED OFF
4μA
VLED
VIN = 3.3V to 4.2V, BRIGHTNESS OFF, Luxeon LED
3.2V
VIN = 3.3V to 4.2V, BRIGHTNESS ON, Luxeon LED
3.4V
VIN = 3.3V to 4.2V, BRIGHTNESS OFF, Luxeon LED
250mA
VIN = 3.3V to 4.2V, BRIGHTNESS ON, Luxeon LED
500mA
LED Ripple Current
VIN = 3.6V
35mAP–P
Switching Frequency
VIN = 3.3V to 4.2V
1.4MHz
Efficiency
VIN = 3.6V, BRIGHTNESS OFF, Luxeon LED
71%
VIN = 3.6V, BRIGHTNESS ON, Luxeon LED
65%
ILED
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DEMO MANUAL DC780A
QUICK START PROCEDURE
Demonstration circuit 780A is easy to set up to evaluate
the performance of the LT1618. Refer to Figure 1 for
proper measurement equipment setup and follow the
procedure below:
NOTE: Make sure that the input voltage does not exceed
4.2V.
NOTE: The IADJ (current adjust) function is optional and
its terminal can be left floating (disconnected) if not being used.
1. Connect the power supply (with power off) LED and
meters as shown in Figure 1.
NOTE: If the LED is not on, make sure that the current
limit on the supply is not set too low.
3. While depressing the ON/OFF button, pulse the BRIGHTNESS button (pulse only for less than one second
intervals) and observe the LED brightness increasing
in a flash-type manner.
4. Once the operation of the LED is established, adjust the
supply within the operating range and observe the LED
brightness, LED forward voltage, efficiency and other
parameters.
2. After all connections are made, turn on input power and
verify that the LED turns on when the ON/OFF button
is depressed.
Figure 1. Proper Measurement Equipment Setup
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2
DEMO MANUAL DC780A
OPTIONAL FUNCTIONS
IADJ (CURRENT ADJUST)
TIMER-CONTROLLED ON/OFF AND FLASH
The ON/OFF and BRIGHTNESS pushbuttons are used to
manually demonstrate how bright a LED is with 250mA and
500mA of LED current. For some applications, adjustable
brightness at levels other than the two constant-current
settings mentioned above is desirable.
The LT1618 has a SHDN pin that is used to control the
LED ON/OFF function on demonstration circuit 780A. The
ON/OFF momentary pushbutton is manually controlled.
An external signal can be used to turn the LED ON and
OFF by replacing the ON/OFF pushbutton and R6 pulldown resistor with an external signal. To control a pulse
of extra-bright light (maximum current) another external
signal can drive a low impedance MOSFET replacing the
BRIGHTNESS momentary pushbutton. This is sometimes
referred to as flash mode and torch mode (lower current,
brightness OFF). Please see Figure 3 for details.
Please see the LT1618 data sheet for more information
on the IADJ pin function.
VIN
ON/OFF
VIN
SW
LT1618
1M
SHDN
ISP
ISN
5.1k
0.1μF
1.65V PWM
GND
VIN
LED ON PULSE
FB
IADJ
NC
SW
LT1618
SHDN
VC
ISP
ISN
DC780A F02
500mA
250mA
Figure 2. Implementation of the IADJ Function Using a 1.65V
10kHz PWM Signal and an RC Filter for LED Dimming.
FB
IADJ
2.2M
GND
NC
VC
FLASH PULSE
DC780A F03
Figure 3. Implementation of the Flash and Torch Modes Using
External Timing Devices. Flash Mode is 500mA Pulsed LED
Current and Torch Mode is 250mA.
100
90
EFFICIENCY (%)
80
BRIGHTNESS OFF
70
60
BRIGHTNESS ON
50
40
30
20
10
0
3.3
3.6
3.9
4.2
VIN (V)
DC780A F04
Figure 4. DC780A Typical Efficiency (TA = 25°C)
LED Used = L × HL – BW02
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DEMO MANUAL DC780A
OPTIONAL FUNCTIONS
C4 MEAN
48.12mV
400ns/DIV
DC780A F05
Figure 5. DC780A LED Has Constant Current
with Low Ripple. LED ON, BRIGHTNESS OFF.
CH4 is LED Current 50mA/DIV
C4 MEAN
47.74mV
400ns/DIV
DC780A F06
Figure 6. DC780A LED Has Constant Current
with Low Ripple. LED ON, BRIGHTNESS ON.
CH4 is LED Current 100mA/DIV
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4
DEMO MANUAL DC780A
OPTIONAL FUNCTIONS
2V
10mVΩ
100μs/DIV
DC780A F07
Figure 7. DC780A LED Turn-On Transient is
Quick and without Overshoot. BRIGHTNESS
OFF. CH1 is LED Forward Voltage, CH4 is
LED Current 50mA/DIV
2V
10mVΩ
100μs/DIV
DC780A F08
Figure 8. DC780A LED Turn-On Transient is
Quick and without Overshoot. BRIGHTNESS
ON. CH1 is LED Forward Voltage, CH4 is
LED Current 100mA/DIV
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DEMO MANUAL DC780A
PARTS LIST
ITEM
QTY
REFERENCE
PART DESCRIPTION
MANUFACTURER/PART NUMBER
Required Circuit Components
1
1
C1
CAP, X5R 1μF 10V 20% 0603
TAIYO YUDEN LMK107BJ105MA
2
1
C2
CAP, X5R 4.7μF 10V 20% 0805
AVX 0805ZD475MAT
3
1
C3
CAP, X5R 0.1μF 10V 10% 0402
AVX 0402ZD104KAT
5
1
D2
DIODE, SCHOTTKY BARRIER
PHILIPS PMEG2010EA
7
1
L1
INDUCTOR, 10μH
COOPER SD25-100
8
1
R1
RES, 124k 1% 1/16W 0402
AAC CR05-1243FM
9
1
R2
RES, 866k 1% 1/16W 0402
AAC CR05-8663FM
10
1
R3
RES, 0.10Ω 1% 1/16W 0603
AAC CRL16-R100FOM
11
1
R4
RES, 2.2MΩ 5% 1/16W 0402
AAC CR05-225JM
12
1
R5
RES, 1MΩ 5% 1/16W 0402
AAC CR05-105JM
15
1
U1
IC, LT1618EDD
LINEAR TECHNOLOGY LT1618EDD
Additional Demo Board Circuit Components
1
0
D1
LED, OPT
OPT
13
0
R6
RES, 0603 OPT
OPT
Hardware/Components (For Demo Board Only)
14
2
SW1, SW2
SWITCH, MOMENTARY, PUSH BUTTON
PANASONIC EVQPJS05K
6
5
E1 TO E5
TURRETS
MILL-MAX-2501-2
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Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
A
B
C
D
4
E1
E4
5
IADJ
GND
E3
E2
3.3V-4.2V
VIN
VLED-
C1
1uF
6.3V
SW1
4
*500mA
PULSE ONLY
250mA/500mA
BRIGHTNESS
1M
R5
OFF / ON
2
SW2
1
5
OPT
U1
2
2.2M
R4
4
9
R6 LT1618EDD
OPT
1
D1
8
Iadj
SHDN
Vin
SD25
L1 10uF
3
1
2
3
Thursday, August 11, 2011
DESIGNER
ENGINEER
APPROVED
CHECKED
MEI
APPROVALS
DRAWN
6
3
0.1uF
C3
Fb
Isn
Isp
SW
CONTRACT NO.
GND
5
7
SW
Vc
10
This circuit is proprietary to Linear Technology and supplied
for use with Linear Technology parts.
Customer Notice:Linear Technology has made a best effort to
design a circuit that meets customer-supplied specifications;
however, it remains the customers responsibility to verify proper
and reliable operation in the actual application, Component
substitution and printed circuit board layout may significantly
affect circuit performance or reliability. Contact Linear
Applications Engineering for assistance.
02/18/04
DATE
1
TECHNOLOGY
1630 McCarthy Blvd.
Milpitas, CA 95035
Phone: (408)432-1900
Fax: (408)434-0507
SCALE:
DWG NO
2
FILENAME: 780A-2.1.DSN
SIZE CAGE CODE
SHEET
DC780A
1
1
OF
1
2.1
REV
WALKER B.
APPROVED
SCH, LT1618EDD, CONSTANT-CURRENT
1.4MHz WHITE LED DRIVER
R1
124k
R2
866k
4.7uF
0.10
D2
C2
R3
VLED+
D1 BECOMES OPTIONAL
2.1
E5
PROTO
08/11/11
DATE
03/16/04
DESCRIPTION
1
2
REVISION HISTORY
REV
PMEG2010EA
2
TITLE
ECO
2
A
B
C
D
DEMO MANUAL DC780A
SCHEMATIC DIAGRAM
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DEMO MANUAL DC780A
DEMONSTRATION BOARD IMPORTANT NOTICE
Linear Technology Corporation (LTC) provides the enclosed product(s) under the following AS IS conditions:
This demonstration board (DEMO BOARD) kit being sold or provided by Linear Technology is intended for use for ENGINEERING DEVELOPMENT
OR EVALUATION PURPOSES ONLY and is not provided by LTC for commercial use. As such, the DEMO BOARD herein may not be complete
in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety
measures typically found in finished commercial goods. As a prototype, this product does not fall within the scope of the European Union
directive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations.
If this evaluation kit does not meet the specifications recited in the DEMO BOARD manual the kit may be returned within 30 days from the date
of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY THE SELLER TO BUYER AND IS IN LIEU
OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS
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ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.
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arising from the handling or use of the goods. Due to the open construction of the product, it is the user’s responsibility to take any and all
appropriate precautions with regard to electrostatic discharge. Also be aware that the products herein may not be regulatory compliant or
agency certified (FCC, UL, CE, etc.).
No License is granted under any patent right or other intellectual property whatsoever. LTC assumes no liability for applications assistance,
customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind.
LTC currently services a variety of customers for products around the world, and therefore this transaction is not exclusive.
Please read the DEMO BOARD manual prior to handling the product. Persons handling this product must have electronics training and
observe good laboratory practice standards. Common sense is encouraged.
This notice contains important safety information about temperatures and voltages. For further safety concerns, please contact a LTC application engineer.
Mailing Address:
Linear Technology
1630 McCarthy Blvd.
Milpitas, CA 95035
Copyright © 2004, Linear Technology Corporation
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Linear Technology Corporation
LT 0911 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2011
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