DC1772A - Demo Manual

DEMO MANUAL DC1772A
LT3761EMSE
High Voltage LED Controller
with Internal PWM Dimming
Description
DC1772A is a high voltage LED controller with internal
PWM dimming. It generates its own PWMOUT waveform
for accurate PWM dimming with up to 25:1 brightness
ratio. It accepts an input voltage from 8V to 60V (8V UVLO
and 9.1V rising turn-on), and drives up to 60V of LEDs
at 1A (when PVIN is less than VLED). DC1772A features
both PWM and analog dimming of the LED string. It has
an OPENLED flag that indicates when the LED string has
been removed.
DC1772A features high efficiency at 350kHz switching
frequency. At high LED string voltages up to 60V and
1A of LED current, the single switch controller has 94%
efficiency. The open LED overvoltage protection uses
the IC’s constant voltage regulation loop to regulate the
output to approximately 69.8V if the LED string is opened
although it may reach 74V peak during transient from
running LEDs to open. The maximum LED string voltage
can be raised from 60V to 65V (or higher) with a simple
change of feedback resistors.
For low input voltage operation, the CTRL pin voltage is
reduced as the input voltage drops below 10V, reducing
LED brightness and restraining the peak switch currents
in order to limit inductor and switch size. UVLO turns the
LEDs off when PVIN drops below 8V.
DC1772A PWM dimming is simplified when compared
with other LED drivers. The LT®3761 generates its own
PWMOUT dimming waveform at a frequency determined
by the capacitance on the PWM pin (C8 gives 300Hz for
DC1772A). The PWMOUT duty cycle is determined by the
voltage on the DIM terminal. Between 0V and 7.7V VDIM
gives between 4% and 96% PWM duty cycle. Information
regarding PWM dimming ratios and performance can be
found in the LT3761 data sheet in the Applications Information section. Analog dimming is also simple to use with
a single voltage source on the CTRL terminal.
Modifications can be made to DC1772A in order to convert
the board to higher or lower power or from an LED driver
to a constant voltage regulator or battery charger. It can
easily be changed from a boost topology to a SEPIC, buck
mode, or buck-boost mode LED driver. Please consult
the factory or the LT3761 data sheet for details. It can be
modified to provide LED+ to GND short-circuit protection
as well.
The LT3761 data sheet gives a complete description of
the part, operation and applications information. The data
sheet must be read in conjunction with this demo manual
for demonstration circuit DC1772A. The LT3761EMSE is
assembled in a 16-lead plastic MSOP MSE package with
a thermally enhanced ground pad. Proper board layout
is essential for maximum thermal performance. See the
data sheet section Layout Considerations.
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.
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DEMO MANUAL DC1772A
Performance Summary
Specifications are at TA = 25°C
PARAMETER
CONDITION
Input Voltage PVIN Range
Operating
Switching Frequency
R6 = 29.4k
ILED
RS2 = 0.25Ω 10V < PVIN < VLED (60V)
Low PVIN ILED (CTRL Foldback)
RS2 = 0.25Ω PVIN = 8.5V
RS2 = 0.25Ω PVIN = 9V
VLED Range
R3 = 1M R4 = 18.2k
PVIN < VLED < 60V
Open LED Voltage
R3 = 1M R4 = 18.2k
69.8V
Typical Efficiency
PVIN = 14V VLED = 60V ILED = 1A PWM = INTVCC
PVIN Under Voltage Lockout (Falling Turn-Off)
R1 = 499k and R2 = 90.9k
8V
PVIN Under Voltage Lockout (Rising Turn-On)
R1 = 499k and R2 = 90.9k
9.1V
INTVCC
Operating
7.85V
Peak Switch Current Limit
RS1 = 0.008Ω
12.5A
PWMOUT Dimming Duty Cycle
VDIM = 7.7V
VDIM = 4V
VDIM = 1.5V
VDIM = 0.4V
96%
50%
10%
4.3%
Internal PWM Dimming Frequency
C8 = 0.047µF 0V < VDIM < 7.7V
VALUE (TYPICAL)
8V to VLED (Up to 60V)
350kHz
1A
930mA
975mA
94%
300Hz
Quick Start Procedure
Demonstration circuit 1772A is easy to set up to evaluate
the performance of the LT3761EMSE. Follow the procedure below:
1.Connect a string of LEDs that will run with forward voltage less than 60V, but greater than PVIN, to the LED+
and LED– terminals on the PCB as shown in Figure 1.
2.Connect the EN/UVLO terminal to GND.
3.With power off, connect the input power supply to the
PVIN and GND terminals. Make sure that the PVIN DC
input voltage will not exceed 60V (or VLED).
4.Connect the DIM terminal to a voltage between 0V and
7.7V to set the internal PWMOUT dimming duty cycle.
If this terminal is left floating the converter will run with
approximately 12% PWMOUT dimming duty cycle. Pull
the PWM terminal high to INTVCC to set the converter
at 100% duty cycle.
2
5.Turn the input power supply on and make sure the
voltage is between 8V and 60V (or VLED).
6.Release the EN/UVLO-to-GND connection.
7.Observe the LED string running at the programmed
LED current and brightness related to the programmed
PWMOUT duty cycle.
8.To change the brightness with PWM dimming, simply
vary the VDIM voltage between 0V and 7.7V with the
PWM terminal floating.
9.To change the brightness with analog dimming, simply
attach a voltage source on the CTRL terminal and reduce
the voltage below 1.2V.
10.Observe the reduction of brightness in the LED string
when PWM or analog dimming.
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DEMO MANUAL DC1772A
Quick Start Procedure
Figure 1. Test Procedure Setup Drawing for DC1772A
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DEMO MANUAL DC1772A
Quick Start Procedure
100%
60VLED 1.0A PWM = INTVCC
98%
96%
EFFICIENCY (%)
94%
92%
90%
88%
86%
84%
82%
80%
0V
5V
10V
15V
20V
25V
30V
35V
40V
45V
50V
55V
60V
PVIN INPUT VOLTAGE (V)
Figure 2. DC1772A Efficiency with 60V LEDs at 1A and 100% PWMOUT Duty Cycle
VDIM = 7.7V
DCPWM = 96%
VDIM = 4V
DCPWM = 50%
ILED
1A/DIV
VDIM = 1.5V
DCPWM = 10%
VDIM = 0.4V
DCPWM = 4.3%
0.5ms/DIV
Figure 3. DC1772A 300Hz PWM Dimming Waveforms at Different PWMOUT Duty Cycles
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DEMO MANUAL DC1772A
Quick Start Procedure
1.2
1.0
ILED (A)
0.8
0.6
under
voltage
lockout
(falling)
0.4
0.2
turn-on
(rising)
0.0
7.5
8
8.5
9
9.5
10
10.5
11
11.5
12
PVIN (V)
Figure 4. DC1772A CTRL LED Current Foldback at Low PVIN with UVLO Falling and Rising
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DEMO MANUAL DC1772A
Parts List
ITEM
QTY
REFERENCE
PART DESCRIPTION
MANUFACTURER/PART NUMBER
Required Circuit Components
1
2
C1, C10
Cap., X7S 4.7µF 100V 10% 1210
TDK C3225X7S2A475K
2
4
C2, C3, C11, C12
Cap., X7R 2.2µF 100V 10% 1210
TDK C3225X7R2A225K
3
1
C4
Cap., X7R 1µF 100V 20% 1206
TDK C3216X7R2A105M
4
1
C5
Cap., X5R 1µF 10V 10% 0603
AVX, 0603ZD105KAT2A
5
1
C6
Cap., X7R 4700pF 25V 20% 0603
AVX, 06033C472MATAT2A
6
1
C7
Cap., X5R 0.01µF 16V 20% 0603
AVX, 0603YD103MAT2A
7
1
C8
Cap., X7R 0.047µF 50V 10% 0603
AVX, 06035C473KAT2A
8
1
D1
Schottky Diode 5A PowerDi5
Diodes Inc. PDS5100H
9
1
L1
Inductor, 10µH HC9-SERIES/COOPER
Cooper Bussmann, HC9-100-R
10
1
M1
MOSFET N-Chan., 100V
Infineon, BSC123N08NS3G
11
1
M2
MOSFET N-Chan., 100V
Siliconix Si2328DS-T1-GE3
12
1
RS1
Res., Chip., 0.008Ω 1/2W 1% 2010
Vishay WSL20108L000FEA
13
1
RS2
Res., Chip., 0.25Ω 1/2W 1% 1206
Vishay WSL1206R2500FEA
14
1
R1
Res., Chip, 499k 0.06W 1% 0402
Vishay CRCW0402499KFKED
15
1
R2
Res., Chip, 90.9k, 0.06W 1% 0402
Vishay CRCW040290K9FKED
16
1
R3
Res., Chip, 1M, 0.1W 1% 0603
Vishay CRCW06031M00FKED
17
1
R4
Res., Chip, 18.2k, 0.06W 1% 0402
Vishay CRCW040218K2FKED
18
1
R5
Res., Chip 10k, 0.06W 5% 0402
Vishay CRCW040210K0JKED
19
1
R6
Res., Chip, 29.4k, 0.06W 1% 0402
Vishay CRCW040229K4FKED
20
1
R7
Res., Chip 1M, 0.06W 5% 0402
Vishay CRCW04021M00JKED
21
1
R8
Res., Chip, 140k, 0.06W 1% 0402
Vishay CRCW0402140KFKED
22
1
R9
Res., Chip 100k, 0.1W 5% 0603
Vishay CRCW0603100KJKEA
23
1
R10
Res., Chip, 124k, 0.1W 1% 0603
Vishay CRCW0603124KFKED
24
1
U1
I.C., LED Driver MSOP(16)-MSE
Linear Tech. Corp. LT3761EMSE
Optional Electrical Components
1
0
C9, C13(OPT)
Cap., 1210
2
0
C14, C15 (OPT)
Cap., 0603
3
0
D2 (OPT)
Rectifier, ESIC SMA
4
0
D3 (OPT)
Diode, 1N4148W, SOD-123
5
0
M3 (OPT)
MOSFET N-Chan., SOT23
(OPT)
6
0
M4 (OPT)
MOSFET P SO8-PWR
(OPT)
7
0
Q1, Q2, Q3 (OPT)
PNP SOT23
(OPT)
8
1
R11
Res., Chip, 0Ω, 1206
Vishay CRCW12060000Z0EA
Vishay CRCW06030000Z0ED
9
1
R12
Res., Chip 0Ω, 0603
10
0
R13, R17, R19-22 (OPT)
Res., 0402
11
0
R14, R24 (OPT)
Res., 0805
12
0
R15 (OPT)
Res., 1206
13
0
R16, R18, R23, R25-R27 (OPT)
Res., 0603
E1-E14
Turret, Testpoint
Optional Hardware
1
6
14
Mill Max 2501-2-00-80-00-00-07-0
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GND
DIM
OPENLED
INTVCC
CTRL
EN/UVLO
PGND
VIN
8V - 60V
PVIN
8V - 60V
124k
0603
R10
R2
90.9k
1%
C5
1uF
R9
100k 10V
0603
R8
140k
1%
R7
1M
1%
R1
499k
1%
C10
4.7uF
100V
1210
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.
RESISTORS ARE IN 0402.
CAPACITORS ARE IN 0603.
14
10
5
ISN
ISP
FB
17
GND
8
1
3
4
2
350kHz
R6
29.4k
1%
11
RT
PWM
PWMOUT
R5
10k
C6
4700pF
DIM/SS VC
OPENLED
C7
U1
0.008
RS1
15 2010
LT3761EMSE
INTVCC
CTRL
VREF
EN/UVLO
PDS5100H
D1
C14
OPT
R4
18.2k
1%
R18
OPT
0603
LED+
C13
OPT
1210
OPT
OPTIONAL for SHORT CIRCUIT
R27
OPT
0603
FB
R26
OPT
0603 D3
C12
2.2uF
100V
1210
INTVCC Q3
OPT
SOT23
0603
R23
OPENLED
C11
2.2uF
100V
1210
OPT
OUT
C3
2.2uF
100V
1210
M3
OPT
OPT.
INTVCC
C8
0.047uF
FB
R3
1.0M
1%
0603 R13
C2
2.2uF
100V
1210
OPTIONAL for BUCK MODE
M1
BSC123N08NS3
GATE SENSE
16
COOPER
R11
0
1206
VIN
0.01uF
9
13
6
R22
OPT
7
12
C4
1uF
100V
1206
C1
4.7uF
100V
1210
NOTE: UNLESS OTHERWISE SPECIFIED
OPT
OUT R17
OPT
0603
OUT R16
OPT
1206
OUT R15
PVIN
L1
10uH
HC9-100-R
OPT
1210
C9
RS2
PVIN
0603
R25 OPT
OPT
M4
OPT
D2
OPT
FB
R19
R21 OPT
OPT
Q1
OPT
SOT23
OUT
0 0603
R12
M2
Si2328DS
OPTIONAL for SHORT CIRCUIT
R20
OPT
C15
R14
OPT
0805
SOT23
OPT
Q2
OUT
OPTIONAL LEVEL SHIFT for BUCK
MODE or BUCK-BOOST MODE
0.25
1%
1/2W
1206
GND
PWM
R24
OPT
0805
LED -
LED +
60VLED
1A
OUT
DEMO MANUAL DC1772A
Schematic Diagram
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7
DEMO MANUAL DC1772A
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
8
dc1772af
Linear Technology Corporation
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1630 McCarthy Blvd., Milpitas, CA 95035-7417
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●
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