Linear DC1772A Quick setup guide

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DEMO MANUAL DC1772A
Description
LT3761EMSE
High Voltage LED Controller
with Internal PWM Dimming
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 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.
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 Infor-
mation 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

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DEMO MANUAL DC1772A
Quick start proceDure
Demonstration circuit 1772A is easy to set up to evaluate
the performance of the LT3761EMSE. Follow the proce-
dure below:
1. Connect a string of LEDs that will run with forward volt-
age 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.
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 avoltage 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.
performance summary
Specifications are at TA= 25°C
PARAMETER CONDITION VALUE (TYPICAL)
Input Voltage PVIN Range Operating 8V to VLED (Up to 60V)
Switching Frequency R6 = 29.4k 350kHz
ILED RS2 = 0.25Ω 10V < PVIN < VLED (60V) 1A
Low PVIN ILED (CTRL Foldback) RS2 = 0.25Ω PVIN = 8.5V
RS2 = 0.25Ω PVIN = 9V
930mA
975mA
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 94%
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 300Hz

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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
Figure 2. DC1772A Efficiency with 60V LEDs at 1A and 100% PWMOUT Duty Cycle
Figure 3. DC1772A 300Hz PWM Dimming Waveforms at Different PWMOUT Duty Cycles
80%
82%
84%
86%
88%
90%
92%
94%
96%
98%
100%
0V 5V 10V 15V 20V 25V 30V 35V 40V 45V 50V 55V 60V
PVIN INPUT VOLTAGE (V)
EFFICIENCY (%)
60VLED 1.0A PWM = INTVCC
Quick start proceDure
ILED
1A/DIV
0.5ms/DIV
VDIM = 7.7V
DCPWM = 96%
VDIM = 4V
DCPWM = 50%
VDIM = 1.5V
DCPWM = 10%
VDIM = 0.4V
DCPWM
= 4.3%

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DEMO MANUAL DC1772A
Figure 4. DC1772A CTRL LED Current Foldback at Low PVIN with UVLO Falling and Rising
Quick start proceDure
0.0
0.2
0.4
0.6
0.8
1.0
1.2
7.5 8 8.5 9 9.5 10 10.5 11 11.5 12
PVIN (V)
ILED (A)
under
voltage
lockout
(falling)
turn-on
(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
9 1 R12 Res., Chip 0Ω, 0603 Vishay CRCW06030000Z0ED
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
Optional Hardware
1 14 E1-E14 Turret, Testpoint Mill Max 2501-2-00-80-00-00-07-0

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DEMO MANUAL DC1772A
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
schematic Diagram
350kHz
RESISTORS ARE IN 0402. CAPACITORS ARE IN 0603. NOTE: UNLESS OTHERWISE SPECIFIED
0603 1206
1A
OPTIONAL for SHORT CIRCUIT
OPTIONAL LEVEL SHIFT for BUCK MODE or BUCK-BOOST MODE
OPTIONAL for SHORT CIRCUIT
OPTIONAL for BUCK MODE
1%
OUT
LED+
FB
PVIN
OUT OUT
OUT
FB
OPENLED
OUT
PVIN
FB
INTVCC
OUT
INTVCC
M1
BSC123N08NS3
M1
BSC123N08NS3
C15 OPT C15 OPT
R6
29.4k 1%
R6
29.4k 1%
M4
OPT
M4
OPT
L1
10uH
COOPER
HC9-100-R
L1
10uH
COOPER
HC9-100-R
C13
OPT
1210 C13
OPT
1210
INTVCCINTVCC
PWMPWM
DIMDIM
R19
OPT
R19
OPT
R24
OPT
0805
R24
OPT
0805
Q3
OPT
SOT23
Q3
OPT
SOT23
R26
OPT
0603 R26
OPT
0603
RS2
0.25
1%
1206
1/2W
RS2
0.25
1%
1206
1/2W
Q2 OPT
SOT23
Q2 OPT
SOT23
GNDGND
OUTOUT
R13
OPT.
R13
OPT.
C14
OPT
C14
OPT
OPENLEDOPENLED
R17
OPT
R17
OPT
R2
90.9k
R2
90.9k R22
OPT
R22
OPT
D1
PDS5100H
D1
PDS5100H
R1
499k
1%
R1
499k
1%
LED + 60VLED LED + 60VLED
R4
18.2k
1% R4
18.2k
1%
PGNDPGND
R21
OPT
R21
OPT
M2
Si2328DS
M2
Si2328DS
C4
1uF 100V 1206
C4
1uF 100V 1206
GNDGND
M3
OPT
M3
OPT
U1
LT3761EMSE
U1
LT3761EMSE
EN/UVLO
12
PWM 8
INTVCC
13
VC
5
DIM/SS
10
VREF
7
CTRL
6
RT
11
VIN
14
ISP 4
ISN 3
PWMOUT 1
GATE
16
FB 2
SENSE
15
GND
17
OPENLED
9
C8
0.047uF
C8
0.047uF
R8
140k 1%
R8
140k 1%
R7
1M 1%
R7
1M 1%
C7
0.01uF
C7
0.01uF
R23
OPT
0603
R23
OPT
0603
VIN
8V - 60V
VIN
8V - 60V
R11
0
1206
R11
0
1206
C1
4.7uF 100V 1210
C1
4.7uF 100V 1210
C11
2.2uF
100V 1210 C11
2.2uF
100V 1210
D2 OPT D2 OPT
R15
OPT
R15
OPT
R27 OPT 0603 R27 OPT 0603
C12
2.2uF
100V 1210 C12
2.2uF
100V 1210
CTRLCTRL
D3
OPT
D3
OPT
R20
OPT
R20
OPT
C6
4700pF
C6
4700pF
R14
OPT 0805
R14
OPT 0805
C5
1uF
10V
C5
1uF
10V
R12
0
0603
R12
0
0603
R16
OPT
R16
OPT
C10
4.7uF 100V 1210
C10
4.7uF 100V 1210
R25 OPT
0603
R25 OPT
0603
Q1
OPT
SOT23
Q1
OPT
SOT23
PVIN
8V - 60V
PVIN
8V - 60V C2
2.2uF 100V 1210 C2 2.2uF 100V 1210
RS1
0.008
2010
RS1
0.008
2010
EN/UVLOEN/UVLO
R9 100k 0603 R9 100k 0603
R5
10k
R5
10k
R18
OPT
0603 R18
OPT
0603
R10
124k
0603
R10
124k
0603
C3 2.2uF 100V 1210 C3 2.2uF 100V 1210
C9
OPT
1210
C9
OPT
1210
R3 1.0M 1% 0603 R3 1.0M 1% 0603
LED -LED -

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DEMO MANUAL DC1772A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] ●FAX: [phone] ●www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2012
LT 1012 • PRINTED IN USA
DEMONSTRATION BOARD IMPORTANT NOTICE
Linear Technology Corporation (LT C ) 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 LT C 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
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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
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