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DEMO MANUAL DC1666A
Description
LT3791
Four-Switch Buck-Boost
LED Driver Controller
Demonstration circuit DC1666A is a synchronous four-
switch buck-boost LED driver controller. It accepts an
input voltage from 4.7V to 60V, and drives up to 25V of
LEDs at 2A. DC1666A features both PWM and analog
dimming of the LED string. It has an OPENLED flag that
indicates when the LED string has been removed and it
has a SHORTLED flag that indicates that the output has
been shorted to GND. In both cases, the IC remains in
control and well protected.
DC1666A features very high efficiency at 300kHz switching
frequency and continuous conduction mode (CCM). The
synchronous four-switch topology both steps up and steps
down voltage while regulating up to 50W of constant LED
output current at efficiencies up to 98%. The circuit can
be altered for applications requiring over 100W of LEDs.
An optional SYNC terminal is provided for synchronizing
to an external clock and CLKOUT terminal provides a
source to sync another converter to the internal clock of
the LT
®
3791.
Three sense resistors provide constant output current
control and monitoring, peak switch current control, and
DC input current limit and monitoring. The ISMON and
IVINMON outputs tell the user how much current is flowing
through the output and input sense resistors.
Small ceramic input and output capacitors are used to
save space and cost. The open LED overvoltage protection
uses the ICs constant voltage regulation loop to limit the
output to approximately 28.3V if the LED string is opened.
For low input voltage operation, the CTRL pin voltage is
reduced as the input voltage drops below 6.5V, reducing
LED brightness and restraining the peak switch currents
in order to limit inductor and switch size. UVLO turns the
LEDs off when VIN drops below 4.7V. When input rises
above 57.6V, overvoltage lockout turns the switches off
to protect them and they turn back on when VIN drops
below 56.2V.
DC1666A PWM dimming is simple. The PWM dimming
MOSFET turns the LED string on and off with an input to
the PWM dimming terminal. For the highest PWM dimming
ratio, it is recommended to use 100Hz as a PWM dimming
frequency. Information regarding PWM dimming ratios and
performance can be found in the Applications Information
section of the LT3791 data sheet. Analog dimming is also
simple with a simple voltage source on the CTRL terminal.
Modifications can be made to DC1666A in order to convert
the board to higher or lower power or from an LED driver
to a constant voltage regulator or battery charger. Please
consult the factory or the LT3791 data sheet for details.
The LT3791 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 DC1666A. The LT3791
is assembled in a 38-lead plastic TSSOP package with
a thermally enhanced ground pad. Proper board layout
is essential for maximum thermal performance. See the
Layout Considerations section in the data sheet.
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 DC1666A
performance summary
(TA = 25°C)
PARAMETER CONDITION VALUE (TYPICAL)
Input Voltage PVIN Range* Operating 4.7V to 60V*
Switching Frequency R12 = 86.6k 300kHz
ILED CTRL = Float, 7V < PVIN < 57.6V 2.0A
VLED Range R7 = 1M, R9 = 44.2k 9.5V < VLED < 25.5V
Open LED Voltage R7 = 1M, R9 = 44.2k 28.3V
Typical Efficiency Boost Region PVIN = 20V, VLED = 25V, ILED = 2A 97.5%
Typical Efficiency Buck-Boost Region PVIN = 24V, VLED = 25V, ILED = 2A 96.8%
Typical Efficiency Buck Region PVIN = 30V, VLED=25V, ILED = 2A 97.3%
Undervoltage Lockout (Falling Turn-Off) R13 = 332k and R6 = 115k 4.7V
Undervoltage Lockout (Rising Turn-On) R13 = 332k and R6 = 115k 5.7V
Overvoltage Lockout (Rising Turn-Off) R11 = 54.9k, R19 = 1M 57.6V
Overvoltage Lockout (Falling Turn-On) R11 = 54.9k, R19 = 1M 56.2V
Peak Switch Current Limit Boost Region RS = 0.004Ω 11A
Valley Switch Current Limit Buck Region RS = 0.004Ω 10A
* The guaranteed input voltage range of the LT3791 is 4.7V to 60V. Overvoltage lockout is set externally at 57.6V on this demo circuit to protect the 60V
MOSFETs M1 and M2. Overvoltage lockout is adjustable.
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DEMO MANUAL DC1666A
Demonstration circuit DC1666A is easy to set up to evaluate
the performance of the LT3791. Follow the procedure below:
NOTE: PWM must be pulled high to run. If PWM is not
used, connect PWM to a 5V source or to INTVCC on the
PCB using 0Ω resistor R22.
1. Connect a string of LEDs that will run with forward volt-
age less than 25.5V, but greater than 9.5V, 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.
4. Connect the PWM terminal. If PWM is not used, connect
PWM to a 5V source or to INTVCC on the PCB using 0Ω
resistor R22. PWM must be pulled high to run.
5. Turn the input power supply on and make sure the
voltage is between 4.7V and 60V.
6. Release the EN/UVLO to GND connection.
7. Observe the LED string running at the programmed
LED current.
8. For PWM dimming, connect a PWM (100Hz or higher is
recommended) signal to the PWM terminal. For analog
dimming, connect a DC voltage between 0V and 2V to
the CTRL terminal.
9. Observe the reduction of brightness in the LED string
when PWM or analog dimming.
Quick start proceDure
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DEMO MANUAL DC1666A
Quick start proceDure
Figure 1. Test Procedure Setup Drawing for DC1666A
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DEMO MANUAL DC1666A
Quick start proceDure
Figure 2. DC1666A Efficiency with 25V LEDs at 2A
Figure 3. DC1666A 100Hz 50:1 PWM Dimming
Waveforms at 12VIN and 25VLED at 2A
INPUT VOLTAGE (V)
0
80
EFFICIENCY (%)
84
88
92
10 20 30 40
3791 TA02b
50
96
100
82
86
90
94
98
60
BUCK
BOOST
BUCK-BOOST
PWM
5V/DIV
IL1
2A/DIV
ILED
2A/DIV
50µs/DIV 3791 TA02c
Figure 4. DC1666A CTRL LED Current Foldback at Low VIN with UVLO Falling and Rising and OVLO
INPUT VOLTAGE (V)
UVLO
(FALLING)
TURN-ON
(RISING)
3
0
ILED (A)
456 7
DC1666A F04
8
1.0
2.0
0.5
1.5
9 10 50 55 60
TURN-ON
(FALLING)
OVLO
(RISING)
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DEMO MANUAL DC1666A
parts List
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Electrical Components
1 1 CSS CAP X7R 0.01µF 50V 10% 0603 AVX, 06035C103KAT2A
2 1 CCCAP X7R 0.022µF 50V 10% 0603 AVX, 06035C223KAT2A 5%
3 4 C2, C3, C12, C14 CAP X7R 2.2µF 100V 10% 1210 AVX, 12101C225KAT2A
4 1 C5 CAP X7R 1µF 100V 10% 1206 AVX, 12061C105KAT2A
5 3 C6, C8, C11 CAP X5R 0.1µF 16V 10% 0402 AVX, 0402YD104KAT2A
6 1 C7 CAP X5R 4.7µF 10V 10% 0603 AVX, 0603ZD475KAT2A
7 4 C9, C10, C13, C15 CAP X7R 4.7µF 50V 10% 1210 AVX, 12105C475KAT2A
8 2 D1-D2 DIODE Single Schottky Barrier Diode SOD-323 NXP, BAT46WJ
9 1 L1 INDUCTOR 10µH Cooper Bussmann, HC9-100-R
10 2 M1, M2 MOSFET N-Channel 60V LFPAK RENESAS, RJK0651DPB-00-J5
11 2 M3, M4 MOSFET N-Channel 40V LFPAK RENESAS, RJK0451DPB-00-J5
12 1 M5 MOSFET N-Channel 40V SOT-23 VISHAY, Si2318DS-T1-E3
13 1 RLED RES CHIP 0.050Ω 1% 2010 VISHAY, WSL2010R0500FEA
14 1 RSRES CHIP 0.004Ω 1W 1% 2010 VISHAY, WSL20104L000FEA
15 1 R7 RES CHIP 1M 1% 0402 VISHAY, CRCW04021M00FKED
16 1 R9 RES CHIP 44.2k 1% 0402 VISHAY, CRCW040244K2FKED
17 1 R12 RES CHIP 86.6k 1% 0402 VISHAY, CRCW040286K6FKED
18 1 U1 IC LT3791EFE 38-LEAD TSSOP VERSION AA TSSOP LINEAR, LT3791EFE#PBF
Optional Electrical Components
1 1 C4 CAP X5R 0.47µF 6.3V 10% 0402 AVX, 04026D474KAT2A
2 0 C16, C17 CAP 1210 OPTIONAL
3 0 C18 CAP 0603 OPTIONAL
4 0 D3, D4 DIODE SMB OPTIONAL
5 2 RC, R16 RES CHIP 0Ω 0402 VISHAY, CRCW04020000Z0ED
6 1 RIN RES CHIP 0.003Ω 1W 1% 1206 IRC, ULR-G-1-1206-R003-1-LF-SLT
7 1 R2 RES CHIP 0Ω 1206 VISHAY, CRCW12060000Z0EA
8 1 R3 RES CHIP 1M 1% 0402 VISHAY, CRCW04021M00FKED
9 2 R4, R5 RES CHIP 200k 5% 0603 VISHAY, CRCW0603200KJNEA
10 1 R6 RES CHIP 115k 1% 0603 VISHAY, CRCW0603115KFKEA
11 1 R8 RES CHIP 237k 1% 0402 VISHAY, CRCW0402237KFKED
12 0 R10, R15, R18, R20, R21 RES CHIP 0402Ω 0402 OPTIONAL
13 1 R11 RES CHIP 54.9k 1% 0402 VISHAY, CRCW040254K9FKED
14 1 R13 RES CHIP 332k 1% 0402 VISHAY, CRCW0402332KFKED
15 1 R14 RES CHIP 0Ω 0603 VISHAY, CRCW06030000Z0EA
16 1 R17 RES CHIP 51Ω 5% 0402 VISHAY, CRCW040251R0JNED
17 1 R19 RES CHIP 1M 1% 0603 VISHAY, CRCW06031M00FKED
18 0 R22, R23 RES CHIP 0Ω 0603 OPTIONAL
Hardware
1 22 E1-E22 TURRET 0.095 MILL-MAX, 2501-2-00-80-00-00-07-0
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dc1666af
DEMO MANUAL DC1666A
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
5
5
4
4
3
3
2
2
1
1
D D
C C
B B
A A
IVINMON
VIN
4.7V - 60V
PVIN
4.7V - 60V
100V
100V
SHORTLED
OPENLED
10V
LED-
GND
LED+
OUT
ISMON
CLKOUT
OVLO
CTRL
EN/UVLO
100V
1206
1210
1210
HC9-100-R
SUMIDA
50V
1210 1210
50V
0603
GND
INTVCC
1210
2010
1206
GND
GND
SYNC
GND
GND
ALL CAPACITORS ARE 0603.
NOTE: UNLESS OTHERWISE SPECIFIED
BAT46WJ BAT46WJ
2010
PWM
300kHz
ALL RESISTORS ARE 0402.
2A
100V 100V
OPENLED
PVIN
INTVCC
INTVCC
OPENLED
INTVCC
VREF
VREF
R2
0
R2
0
M2
RJK0651DPB
M2
RJK0651DPB
C17
(OPT)
C17
(OPT)
C18
OPT
C18
OPT
Rc
0
Rc
0
E12E12
C15
4.7uF
50V
1210
C15
4.7uF
50V
1210
M3
RJK0451DPB
M3
RJK0451DPB
C14
2.2uF
1210
C14
2.2uF
1210
D3
OPT
D3
OPT
E2E2
R8
237k
R8
237k
R6
115k
0603
R6
115k
0603
R17
51
R17
51
R7
1M
R7
1M
R12
86.6k
R12
86.6k
E8E8
C2
2.2uF
C2
2.2uF
M5
Si2318DS
M5
Si2318DS
RIN 0.003
RIN 0.003
E11E11
M4
RJK0451DPB
M4
RJK0451DPB
C12
2.2uF
1210
C12
2.2uF
1210
E3E3
E14E14
C9
4.7uF
C9
4.7uF
R14
0
0603
R14
0
0603
E21E21
R22 OPT
0603
R22 OPT
0603
R19
1M
R19
1M
R18
OPT
R18
OPT
D1D1
E7E7
L1 10uHL1 10uH
M1
RJK0651DPB
M1
RJK0651DPB
C8
0.1uF
0402
C8
0.1uF
0402
R21
OPT
R21
OPT
U1
LT3791EFE
U1
LT3791EFE
EN/UVLO
9
SHORTLED
5
OPENLED
4
IVINN 11
CTRL
1
PWM 3
ISP 25
SYNC
34
SS
2
PWMOUT 31
VC
36
RT
35
TEST2 32
IVINMON
8
ISMON
7
IVINP 10
CLKOUT
33
VREF
6
OVLO
38
SNSN 28
SNSP 27
ISN 26
PGND
17 PGND
20
FB 37
TG2 24
SW2 21
BG2 19
BG1 18
SW1 16
TG1 14
BST1 15
BST2 22
NC
23
VIN 12
INTVCC 13
SGND
30
PGND
39
TEST1
29
C3
2.2uF
C3
2.2uF
Cc
22nF
Cc
22nF
C16
(OPT)
C16
(OPT)
C4 470nF
0402
C4 470nF
0402
C11
0.1uF
0402
C11
0.1uF
0402
D4
OPT
D4
OPT
E13E13
R11
54.9k
R11
54.9k
R20 OPTR20 OPT
E15E15
C7
4.7uF
C7
4.7uF
R5
200k
0603
R5
200k
0603
R15 OPTR15 OPT
M6
OPT
M6
OPT
C13
4.7uF
50V
1210
C13
4.7uF
50V
1210
R4
200k
0603
R4
200k
0603
C5
1uF
C5
1uF
Css
10nF
Css
10nF
E10E10
E17E17
D2D2
E20E20
RLED
0.05
RLED
0.05
E22E22
R13
332k
R13
332k
E5E5
E6E6
R10
OPT
R10
OPT C10
4.7uF
C10
4.7uF
R16 0R16 0
E18E18
R9
44.2k
R9
44.2k
R23 OPT
0603
R23 OPT
0603
RS
0.004
RS
0.004
C6
0.1uF
0402
C6
0.1uF
0402
E16E16
E4E4
E1E1
E9E9
R3
1M
R3
1M
E19E19
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dc1666af
DEMO MANUAL DC1666A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
LINEAR TECHNOLOGY CORPORATION 2012
LT 0312 • PRINTED IN USA
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 applica-
tion engineer.
Mailing Address:
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1630 McCarthy Blvd.
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Copyright © 2004, Linear Technology Corporation
