DC2176A - Demo Manual

DEMO MANUAL DC2176A
LT3909
2-String × 60mA, 2MHz Step-Up LED
Driver with ±2% Current Matching
Description
Demonstration circuit 2176A features the LT®3909, a
2-string × 60mA, 2MHz step-up LED driver with ±2%
current matching.
The LT3909 precisely regulates two LED strings for equal
current, supports LED dimming that reduces brightness
down to a 1/40,000 ratio, protects against faults and also
reports faults. The LT3909 consists of a step-up converter
with a fixed 2MHz switching frequency and current sources
for the LED strings.
The operating voltage range for DC2176A is from 7V to
36V. The maximum current in each LED string is 40mA
and is programmed by 24.9k ISET resistor R1. The ISET
resistor can be changed to 20k or 16.7k to program the
string current to 50mA or 60mA respectively. 16.7k is a
0.1% resistor—a 1% 16.9k resistor will result in slightly
less than 60mA string current. See the data sheet for application examples with 50mA and 60mA string currents.
The LT3909 utilizes voltage feedback during PWM dimming and when there are faults on both LED strings. Voltage feedback resistors R2 and R3 on DC2176A optimize
operation for LEDs that are 35V maximum. Efficiency is
86% at 12V input, 35V for the LED string forward voltages
and 40mA per string.
LED current can be reduced by an external voltage applied
to the CTRL terminal. Resistor R8 pulls up CTRL to the
INTVCC voltage of the LT3909 so the LED current is at the
40mA maximum when there is no external CTRL voltage
applied. There are placeholders to add voltage dividers
either from VIN or INTVCC to the CTRL pin. A voltage
divider from VIN to the CTRL pin can be used to reduce
LED current at low input voltages. A resistor divider from
INTVCC to CTRL allows an NTC to reduce LED current at
high temperatures. There are placeholders for an RC filter
between the CTRL terminal and the CTRL pin. The RC filter
limits the ramp time of the CTRL pin and prevent false
faults when CTRL ramps too quickly. The FAULT terminal
is pulled up by 100k R6 to VIN, but there is a placeholder
to pull up FAULT to INTVCC instead.
Resistor divider R4 and R5 from the input to the EN/UVLO
pin programs the circuit to turn off when VIN decreases
below 5V with 0.9V of hysteresis. The circuit can also be
turned off by connecting the EN/UVLO terminal to ground.
An external voltage must be applied to the PWM terminal
in order for DC2176A to operate. The external voltage can
be a DC level or an appropriate PWM dimming signal. A
common frequency for PWM dimming is 100Hz. There is
a placeholder for a resistor to pull up PWM to INTVCC so
an external voltage on PWM for operation is unnecessary.
There is a placeholder that allows an external diode to
be placed in parallel with the internal LT3909 rectifier for
higher current capability. DC2176A uses an inductor that
is optimized for high efficiency, and the input supply for
power to the inductor can be separated from the LT3909
VIN pin to allow operation from two input sources. Ceramic
capacitors are used at the input, output and for INTVCC. A
50V tantalum polymer capacitor protects the input from
ringing that may occur when the input is hot-plugged using
long leads. There are placeholders occupied by 0805 size
0Ω jumpers on the back of the PCB for two LED strings
and also placeholders for SOD323 diodes to clamp the
LED1 and LED2 voltages from ringing below ground.
2-string operation, close current matching, an extremely
wide dimming range and fault protection make the LT3909
ideal for functionally advanced back lighting and illumination circuits. DC2176A features the LT3909EDD in a
thermally enhanced 12-lead 3mm × 3mm DFN package.
The LT3909 data sheet must be read in conjunction with
this demo manual to properly use or modify DC2176A.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2176A
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.
dc2176afa
1
DEMO MANUAL DC2176A
Performance Summary
Specifications are at TA = 25°C
PARAMETERS
CONDITIONS
MIN
Minimum Input Voltage, VIN
VLED1 = VLED2 = 35V, ILED1 = ILED2 ≤ 40mA
TYP
MAX
7
UNITS
V
Maximum Input Voltage, VIN
VLED1 = VLED2 = 35V, ILED1 = ILED2 ≤ 40mA
36
V
Maximum LED Voltage, VLED1, VLED2
R2 = 976k 1%, R3 = 31.6k 1%
35
V
LED Current, ILED1, ILED2
R1 = 24.9k, VCTRL = INTVCC
40
mA
Input EN/UVLO Turn-On Voltage, VIN
R4 = 402k, R5 = 130k, VIN Rising
5.9
V
Input EN/UVLO Turn-Off Voltage, VIN
R4 = 402k, R5 = 130k, VIN Falling
5
V
Efficiency
VIN = 12V, VLED1 = VLED2 = 35V, ILED1 = ILED2 = 40mA
86
%
2
MHz
Switching Frequency
Quick Start Procedure
To evaluate the performance of the LT3909 using DC2176A,
refer to Figure 1 for the proper measurement equipment
setup and then follow the procedure below:
NOTE: An external voltage must be applied to the PWM
terminal in order for DC2176A to operate. See Step 4 for
details.
1.Connect two strings of LEDs with a forward voltage of
35V or less and corresponding meters.
2.Connect the EN/UVLO terminal to GND with a clip-on
lead.
3.With the power off, connect the input power supply and
corresponding meters.
4.Apply an external voltage to the PWM terminal. The
external voltage can be a 2V to 5V DC source or a 100Hz
or higher PWM dimming signal. Install resistor R10 to
pull up PWM to INTVCC if an external voltage on PWM
is not desired.
5.Turn the VIN power supply on and verify that the input
voltage is between 7V and 36V. The VIN voltage is allowed to exceed the LED voltage by a few volts, but
a VIN that is much higher than the LED voltages may
activate overtemperature protection or dissipate too
much power in the LT3909.
6.Release the EN/UVLO to GND connection.
7.Once the LED strings are running at the programmed
LED current; adjust the input voltage within the operating range and observe the LED current regulation or
reduction in brightness with LED dimming.
dc2176afa
2
DEMO MANUAL DC2176A
Quick Start Procedure
Figure 1. Proper Measurement Equipment Setup for DC2176A
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
VLED1 = VLED2 = 35V
ILED1 = ILED2 = 40mA
5
10
15
25
20
VIN (V)
30
35
40
DC2176a F02
Figure 2. Efficiency vs Input Voltage VIN with VLED1 = VLED2 = 35V and ILED1 = ILED2 = 40mA
dc2176afa
3
DEMO MANUAL DC2176A
Quick Start Procedure
90
80
TURN-OFF
60
50
40
30
TURN-ON
ILED1 + ILED2 (mA)
70
20
10
0
VLED1 = VLED2 = 35V
0
5
10
15
20
VIN (V)
25
30
35
40
DC2176a F03
Figure 3. Total Output Current ILED1 + ILED2 vs Input Voltage VIN with VLED1 = VLED2 = 35V. UVLO Occurs
at VIN = 5V Input Falling with 0.9V of Hysteresis
VOUT
20V/DIV
VIN = 12V
VLED1 = VLED2 = 35V
ILED1 = ILED2 = 40mA
ILED1
20mA/DIV
ILED2
20mA/DIV
VPWM
2V/DIV
500ns/DIV
DC2176a F04
Figure 4. LED Current When Brightness is Reduced to a 1/20,000 Ratio by PWM Dimming at 100Hz
dc2176afa
4
DEMO MANUAL DC2176A
Parts List
ITEM
QTY
REFERENCE
PART DESCRIPTION
MANUFACTURER/PART NUMBER
Required Circuit Components
1
1
C1
Cap, 1µF X7R 50V 10% 0805
Murata GRM21BR71H105KA12L
2
1
C2
Cap, 2.2µF X7R 50V 20% 1206
TDK C3216X7R1H225M
3
1
C3
Cap, 1µF X5R 6.3V 20% 0603
TDK C1608X5R0J105M
4
1
L1
Inductor, 6.8µH 4020
Wurth Electronik 74437324068
5
1
R1
Res, Chip 24.9k 0.06W 1% 0603
Vishay CRCW060324K9FKEA
6
1
R2
Res, Chip 976k 0.01W 1% 0603
Vishay CRCW0603976KFKEA
7
1
R3
Res, Chip 31.6k 0.10W 1% 0603
Vishay CRCW060331K6FKEA
8
1
R4
Res, Chip 402k 0.06W 1% 0603
Vishay CRCW0603402KFKEA
9
1
R5
Res, Chip 130k 0.06W 1% 0603
Vishay CRCW0603130KFKEA
10
1
U1
IC, LED Driver DFN(12) (DD) 3mm × 3mm
Linear Technology Corporation LT3909EDD#PBF
Additional Demo Board Circuit Components
1
0
C4 (Opt)
Cap, 10nF X7R 100V 10% 0603
AVX 06031C103KAT2A
2
1
C5
Cap, Tant Polymer 10µF 50V 20% 7343
AVX TCJD106M050R0120
3
0
D1 (Opt)
Schottky Diode, 1A SOD-323
Diodes Inc SBR1A40S3
4
1
R6
Res, Chip 100k 0.06W 5% 0603
Vishay CRCW0603100KJEA
5
0
R7, R9, R10, R11 (Opt)
Res, 0603
6
1
R8
Res, Chip 100k 0.06W 1% 0603
7
1
R12
Res, Chip 1k 0.06W 5% 0603
8
28
R13, R14, R15, R16, R17, R18, R19, Res/Jumper, Chip 0 0.125W 0805
R20, R21, R22, R23, R24, R25, R26,
R27, R28, R29, R30, R31, R32, R33,
R34, R35, R36, R37, R38, R39, R40
Vishay CRCW0603100KFKEA
Vishay CRCW06031K00JEA
Vishay CRCW08050000ZOEA
Hardware: For Demo Board Only
1
12
E1, E2, E3, E4, E5, E6 ,E7, E8, E9,
E10, E11, E12
Turret, Testpoint
Mill Max 2501-2-00-80-00-00-07-0
2
4
MH1 to MH4
Stand-Off, Nylon 1/4" Tall (Snap On)
Keystone, 8831(Snap On)
dc2176afa
5
6
GND
VIN
7V‐36V
GND
GND
FAULT
PWM
CTRL
EN/UVLO
E8
E7
E6
E5
E4
E3
E2
E1
R6
100k
5%
R9
(Opt)
R11
(Opt)
C5
+ 10µF
50V
7343
R8
100k
R10
(Opt)
R7
(Opt)
C3
1µF
R5
130k
1k
5%
R12
24.9k
R1
C1
R4
1µF
402k 50V
0805
TP2
GND
TP1
C4
10nF
(Opt)
8
7
5
4
1
3
2
L1
FAULT
PWM
CTRL
ISET
INTVCC
EN/UVLO
VIN
13
GND
U1
LT3909EDD
SW
LED2
LED1
FB
VOUT
6.8µH
74437324068
R3
31.6k
R2
976k
E12
E11
E10
E9
*
GND
GND
*
LED2
35V LED
LED1
35V LED
C2
2.2µF
50V
1206
THE PERFORMANCE SUMMARY
* SEE
FOR LED CURRENT RATING
SBR1A40S3
(Opt)
D1
1. ALL RESISTORS AND CAPACITORS 0603.
2. ALL RESISTORS ARE 1%.
NOTE: UNLESS OTHERWISE SPECIFIED
9
10
6
11
12
DEMO MANUAL DC2176A
Schematic Diagram
dc2176afa
DEMO MANUAL DC2176A
Schematic Diagram
R19
0Ω
0805
R32
0Ω
0805
R18
0Ω
0805
R20
0Ω
0805
R31
0Ω
0805
R33
0Ω
0805
R17
0Ω
0805
R21
0Ω
0805
R30
0Ω
0805
R34
0Ω
0805
R16
0Ω
0805
R22
0Ω
0805
R29
0Ω
0805
R35
0Ω
0805
R15
0Ω
0805
R23
0Ω
0805
R28
0Ω
0805
R36
0Ω
0805
R14
0Ω
0805
R24
0Ω
0805
R27
0Ω
0805
R37
0Ω
0805
R13
0Ω
0805
R25
0Ω
0805
R26
0Ω
0805
R38
0Ω
0805
R40
0Ω
0805
R39
0805
dc2176afa
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.
7
DEMO MANUAL DC2176A
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
FOR ANY PARTICULAR PURPOSE. EXCEPT TO THE EXTENT OF THIS INDEMNITY, NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR
ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.
The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user releases LTC from all claims
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
dc2176afa
8
Linear Technology Corporation
LT 0516 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2015
Similar pages