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DEMO MANUAL DC1827A
Description
LT3795
110V LED Controller with Spread
Spectrum Frequency Modulation
Demonstration Circuit 1827A features a 110V LED con-
troller with spread spectrum frequency modulation - the
LT
®
3795. Unlike most boosts, the circuit disconnects the
output to protect against shorts or other fault conditions
when the input voltage exceeds the output. The input volt-
age range for normal operation is from 8V to 60V. OVLO
becomes active for inputs above 63V and the maximum
input voltage is 110V. The LED current is 400mA and the
switching frequency is 250kHz. The efficiency is 92% when
the input is 12V and the LED voltage is at 87V which is
the maximum LED voltage.
Spread spectrum switching is available to simplify conduct-
ed emissions compliance. There is a 47nF capacitor from
the RAMP pin to ground to set the rate at which frequency
modulation occurs, but resistor R20 shorting the RAMP pin
capacitor must be removed to activate spread spectrum.
OVLO and EN/UVLO are both set using resistor dividers.
EN/UVLO is set so the circuit will UVLO when the input
voltage falls below 6V and will turn on when the input
voltage rises above 7.5V.
Current sense resistors program LED current and input
regulation current and also determine the monitoring
voltages that indicate output and input current. The LED
current is set by RS2. ISMON provides a 2.5V/1A voltage
that is used to monitor the LED current. Input current
regulation occurs at 4A and is set by RS3. IVINCOMP
provides a 300mV/1A voltage that is used to monitor
the input current. Capacitor C11 on the IVINCOMP pin
provides compensation for the input current regulation
loop. CTRL1 and CTRL2 are analog dimming inputs that
allow external voltages to reduce the LED current from the
programmed maximum. CTRL1 and CTRL2 are pulled up to
the VREF pin by 100k resistors. SHORTLED and OPENLED
are open-collector status flag outputs that are pulled up
to the INTVCC pin voltage.
The circuit requires application of an external voltage to
the PWM terminal for operation. The external voltage can
be a DC level or an appropriate pwm dimming signal. A
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.
common frequency for PWM dimming is 100Hz. The
high-side PMOS FET that is used for pwm dimming also
disconnects the output to protect against shorts.
The soft-start pin (SS) is configured so the circuit will hiccup
when a fault occurs and will not latch off. The demo circuit
also supports the adjustment capability of the LT3795 for
switching frequency and feedback loop compensation.
The FB pin is programmed using a resistor divider to
limit the output voltage in case there is no LED string on
the output. When an open LED transient occurs either at
start up or because the LED string opens, the peak output
voltage may overshoot to 100V but FB will regulate the
settled output voltage to 95V.
The demo circuit uses ceramic input and output capacitors.
An aluminum electrolytic capacitor can be easily added to
the input if it is necessary for stability during conducted
emissions testing. The 120V switching MOSFET allows
110V on the input. FB programming inhibits switching at
high output voltages so the 100V rating of the rectifier is
not exceeded.
The demo circuit is designed to be easily reconfigured
to buck mode, buck-boost mode and SEPIC topologies.
There are example schematics in the data sheet. Consult
the factory for assistance.
Maximum input and output voltages of 110V, spread
spectrum switching, fault protection and full monitoring
make the LT3795 attractive for high voltage and high
power LED circuits, battery chargers and voltage regula-
tors that require an accurate current limit. DC1827A uses
the LT3795EFE which is packaged in a thermally enhanced
28-lead TSSOP. The LT3795 data sheet must be read in
conjunction with this demo manual to properly use or
modify DC1827A.
Design files for this circuit board are available at
http://www.linear.com/demo/DC1827A
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DEMO MANUAL DC1827A
Quick start proceDure
It is easy to set up DC1827A to evaluate the performance
of the LT3795. Follow the procedure below:
NOTE: PWM must be pulled high to work. If PWM is not
used, connect the PWM terminal to a 2V to 5V DC source
or connect the PWM pin to VREF on the PCB using R18.
1. Connect a string of LEDs with a forward voltage of 87V
or less, but greater than the PVIN voltage, to the LED+
and GND terminals on the PCB as shown in Figure 1.
2. Connect the EN/UVLO terminal to GND.
3. With the power off, connect the input power supply to
the PVIN and GND terminals within the voltage range
specified on the PCB. Make sure that the input power
supply voltage does not exceed the forward voltage of
the LED string. OVLO becomes active to inhibit switch-
ing for an input voltage greater than 63V.
4. Connect an input to the PWM terminal. If PWM is not
used, connect PWM to a 2V to 5V DC source or to VREF
on the PCB using resistor R18. PWM must be pulled
high to work. For PWM dimming, connect a 100Hz or
higher PWM signal to the PWM terminal.
5. Turn the PVIN power supply on.
6. Release the EN/UVLO to GND connection.
7. Observe the LED string running at the programmed
LED current; or, observe the reduction of brightness
in the LED string with PWM dimming.
performance summary
Specifications are at TA = 25°C
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Input, VPVIN VLED = 87V, ILED ≤ 400mA 8 V
Maximum Input – Switching,VPVIN VLED = 87V, ILED ≤ 400mA 60 V
Maximum Input – Not Switching, VPVIN VOVLO ≥ 1.25V 110 V
Maximum LED Voltage, VLED 87 V
LED Current, ILED RS2 = 0.62Ω 400 mA
Input EN Voltage, VPVIN(EN) VPVIN Rising R1 = 499k, R2 = 115k, R3 = 12.4k 7.5 V
Input UVLO Voltage, VPVIN(UVLO) VPVIN Falling R1 = 499k, R2 = 115k, R3 = 12.4k 6 V
Input OVLO Turn-Off Voltage, VPVIN(OVLO_TURN-OFF) VPVIN Rising R1 = 499k, R2 = 115k, R3 = 12.4k 63.1 V
Input OVLO Turn-On Voltage, VPVIN(OVLO_TURN-ON) VPVIN Falling R1 = 499k, R2 = 115k, R3 = 12.4k 62.1 V
Efficiency VPVIN =12V, VLED = 87V, ILED = 400mA
VPVIN =24V, VLED = 87V, ILED = 400mA
VPVIN =48V, VLED = 87V, ILED = 400mA
92
91
92
%
%
%
Switching Frequency R5 = 31.6k 250 kHz
Input Current Limit RS3 = 0.015Ω 4 A
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DEMO MANUAL DC1827A
Figure 1. Proper Measurement Equipment Setup for DC1827A
Quick start proceDure
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DEMO MANUAL DC1827A
Quick start proceDure
Figure 2. Conducted Emissions without Spread Spectrum (RAMP
Pin Grounded) and the Improvement that Occurs with Spread
Spectrum Switching (47nF at RAMP Pin)
Figure 3. DC1827A Efficiency with 87VLED at 400mA
Figure 4. The LED String is 87V. This Output Current vs Input
Voltage Graph Shows the Wide Input Voltage Range and the
Input Voltages at Which UVLO, Turn-On and OVLO Occur. Input
Current Limit Occurs When VIN Is 10V or Less.
Figure 5. LED Current During PWM Dimming at 100Hz
FREQUENCY (kHz)
0
AMPLITUDE (dBµV)
20
40
100
10
30
50
60
80
70
90
200 250 300
DC1827A F02
350150
RAMP PIN GROUNDED
47nF AT RAMP PIN
EMI AVERAGE
SA DETECTOR
PVIN (V)
70
EFFICIENCY (%)
80
75
85
100
90
95
20 30 40 50 60
DC1827A F03
700 10
87VLED 400mA
PVIN (V)
–0.05
LED CURRENT (A)
0.05
0.15
0.45
0
0.10
0.20
0.25
0.35
0.30
0.40
5 110
DC1827A F04
1150 60 6510
87VLED
DC1827A F05
12VIN, 87VLED 400mA
750 TO 1
200 TO 1
500 TO 1
100 TO 1 67 TO 1
20µs/DIV
ILED
100mA/DIV
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DEMO MANUAL DC1827A
parts List
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 1 C1 Cap., X7R 1µF 100V 20% 1206 AVX 12061C105MAT2A
2 7 C2, C3, C4, C7, C8, C9 Cap., X7R 2.2µF 100V 10% 1210 Murata GRM32ER72A225KA35L
C10
3 1 C5 Cap., X5R 4.7µF 10V 10% 0603 AVX 0603ZD475KAT2A
4 1 C6 Cap., X7R 0.1µF 25V 10% 0603 AVX 06033C104KAT2A
5 1 C12 Cap., X7R 0.01µF 10V 10% 0603 AVX 0603ZC103KAT1A
6 1 D1 Schottky Diode 5A POWERDI5 Diodes Inc. PDS5100-13
7 1 L1 Inductor, 22µH HC9-SERIES Cooper Bussmann HC9-220-R
8 1 M1 Mosfet N-Channel, 120V/44A Super SO8 Infineon BSC190N12NS3G
9 1 M2 Mosfet P-Channel, 150V PowerPak 1212-8 Vishay Siliconix Si7115DN-T1-E3
10 1 RS1 Res., LRC 0.015 0.5W 1% 2010 IRC LRC-LR2010LF-01-R015-F
11 1 RS2 Res., LRC 0.620 0.5W 1% 2010 SEI CSRN2010FKR620
12 1 R4 Res., Chip 1.00M 0.06W 1% 0603 NIC NRC06F1004TRF
13 1 R5 Res., Chip 31.6k 0.06W 1% 0402 Vishay CRCW040231K6FKED
14 1 R6 Res., Chip 13.3k 0.06W 1% 0402 Vishay CRCW040213K3FKED
15 1 R7 Res., Chip 10k 0.06W 5% 0402 Vishay CRCW040210K0JNED
16 1 U1 I.C., LED Driver TSSOP28-FE/EB Linear Tech. Corp. LT3795EFE
Optional Demo Circuit Components
1 1 C13 Cap., X5R 0.1µF 25V 10% 0603 AVX 06033C104KAT2A
21 C11 Cap., X7R 0.01µF 10V 10% 0603 AVX 0603ZC103KAT1A
3 1 C14 Cap., X7R 0.047µF 16V 10% 0603 AVX 0603YC473KAT1A
4 0 C15, C16, C17, C18, Cap., 1210
C19
5 0 C20 Cap., 0402
6 0 C21 Cap., 12.5mm Dia.
7 1 D2 Ultra Fast Rect., 150V/1A SMA Fairchild Semi. ES1C
8 0 M3 Mosfet N-Channel SOT23
9 0 Q1,Q2 Trans., PNP SOT23 Zetex FMMT593
10 1 RS3 Res., LRC 0.015 0.5W 1% 2010 IRC LRC-LR2010LF-01-R015-F
11 1 R1 Res., Chip 499k 0.06W 1% 0603 Vishay CRCW0603499KFKEA
12 1 R2 Res., Chip 115k 0.06W 1% 0402 Vishay CRCW0402115KFKED
13 1 R3 Res., Chip 12.4k 0.06W 1% 0402 Vishay CRCW040212K4FKED
14 1 R8 Res./Jumper, Chip 0Ω 1/4W 1A 1206 Vishay CRCW12060000ZOEA
15 0 R9 Res., 1206
16 0 R10, R15, R19, R22 Res., 0402
17 1 R11 Res/Jumper, Chip 0Ω 1/16W 1A 0402 Vishay CRCW04020000Z0ED
18 0 R12, R13, R14, R18, R21,
R23, R24, R25, R26, R27,
R30, R31, R32
Res., 0603
19 4 R16, R17, R28, R29 Res., Chip 100k 0.06W 5% 0402 Vishay CRCW0402100KJNED
20 1 R20 Res./Jumper, Chip 0Ω 1/16W 1A 0603 Vishay CRCW06030000Z0EA
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DEMO MANUAL DC1827A
parts List
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Hardware
1 18 E1, E2, E3, E4, E5, E6, E7, E8,
E9, E10, E11, E12, E13, E14,
E15, E16, E17, E18
Turret, Testpoint Mill Max 2501-2-00-80-00-00-07-0
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DEMO MANUAL DC1827A
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
IVINN
R14
(OPT)
0603
RS2
0.620
1%
2010
R22
(OPT)
R17
100k PVIN
R4
1.00M
1%
0603
VOUT
E5
CTRL1
INTVC C
E4
GND
C2
2.2uF
100V
1210
R29
100k
E16
SHORTLED
R28
100k E17
OPENLED
RS3
0.015
1%
2010
C16
(OPT)
1210
R25
(OPT)
0603
L1
22uH
Cooper Bussmann
HC9-220-R
E3
VIN
8V - 60V
110V MAX.
63V OVLO
C15
(OPT)
1210
R21
(OPT)
0603
/OPENLED
R5
31.6k
1%
250kHz
R26
(OPT)
0603
Q1
SOT23
(OPT)
C20
(OPT)
0402
R6
13.3k
1%
WARNING!
C11
0.01uF
E15
IVINCOMP
RS1
0.015
1%
2010
VO LT A GE
HIGH
IVINN
C3
2.2uF
100V
1210
C4
2.2uF
100V
1210
C7
2.2uF
100V
1210
C8
2.2uF
100V
1210
C9
2.2uF
100V
1210
INTVCC
E6
CTRL2
VOUT
E14
GND
R23
(OPT)
0603
C1
1uF
100V
1206
M1
BSC190N12NS3G
C10
2.2uF
100V
1210
C12
0.01uF
R16
100k
D1
PDS5100-13
R3
12.4k
1%
E1
EN/UVLO
E9
GND
VREF
C5
4.7uF
10V
R13
(OPT)
0603
E11
VOUT
R32
(OPT)
0603
PVIN
R2
115k
1%
C19
(OPT)
1210
C6
0.1uF
PVIN
C18
(OPT)
1210
E2PVIN
8V - 60V
110V MAX.
63V OVLO
/OPENLED
E7
PWM
R18
(OPT)
0603
R7
10k
R11
0 Ohm
R12
(OPT)
0603
R9
(OPT)
1206
R19
(OPT)
U1
LT3795EFE
VIN
23
OVLO
25
GND
29
EN/UVLO
24
VREF
10
CTRL1
9
PWM
14
RA MP
13
SS
11
ISMON
5
GND
4
GND
17
GND
21
GND
22
VC 8
RT
12
SHORTLED 15
OPENLED 16
IVINP
27
IVINN
26
IVINCOMP 28
CTRL2
6
FB 7
ISP 1
ISN 2
TG 3
GATE
19
SENSE 18
INTVCC
20
+
C21
(OPT)
12.5mm DIA. SMD
E10
GND
R1
499k
1%
0603
VREF
M3
(OPT)
SOT23
E18
GND
R20
0 Ohm
0603
VOUT
C17
(OPT)
1210
R24
(OPT)
0603 R31
(OPT)
0603
VOUT
M2
Si7115DN-T1-E3
PVIN
C13
0.1uF
E12 LED+
400mA
87V
E13
GND
Q2
(OPT)
SOT23
R10
(OPT)
C14
0.047uF
R15
(OPT)
R8
0 Ohm
1206
R30
(OPT)
0603
D2
ES1C
R27
(OPT)
0603
E8
ISMON
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dc1827af
DEMO MANUAL DC1827A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
LINEAR TECHNOLOGY CORPORATION 2013
LT 0713 • 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
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 LT C 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. LT C assumes no liability for applications assistance,
customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind.
LT C 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 LT C applica-
tion engineer.
Mailing Address:
Linear Technology
1630 McCarthy Blvd.
Milpitas, CA 95035
Copyright © 2004, Linear Technology Corporation
