Linear Technology DC2257A Quick setup guide

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DEMO MANUAL DC2257A
DESCRIPTION
LTM8005
38VIN, 38VOUT Boost µModule
LED Driver with 40V Switch
Demonstration circuit 2257A features the LT M
®
8005 – a
38VIN, 38VOUT boost μModule
®
LED driver that can dis-
connect the output to protect against faults and provides
spread spectrum switching to simplify emissions compli-
ance. DC2257A is an LED driver with an input range for
normal operation from 6Vto27V. OVLO becomes active for
inputs above 29V and the maximum input voltage is 38V.
The LED current is 1.2A and the base switching frequency
is 350kHz. The efficiency is 92% when the input is 12V
with a 35V LED load. 35V is the maximum LED voltage.
The demo 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.
Common frequencies for PWM dimming are 100Hz or
higher. Analog dimming is achieved using the CTRL inputs.
DC2257A allows adjustments to output voltage, output
current, input current, switching frequency, frequency L, LT, LTC, LTM, Linear Technology, the Linear logo and μModule are registered trademarks of
Linear Technology Corporation. All other trademarks are the property of their respective owners.
BOARD PHOTO
modulation rate including disable, feedback loop com-
pensation, EN/UVLO threshold, OVLO threshold, soft-
start period, and fault latch-off or hiccup. In most cases,
adjustment is made by modifying the appropriate resistor
or capacitor component(s).
DC2257A provides outputs for input and output current
monitoring and fault status for short and open LEDs.
The demo circuit is designed to be easily reconfigured
to buck mode, buck-boost mode and SEPIC topologies.
There are placeholders to mount optional LC input filter
components.
The LTM8005 data sheet must be read in conjunction with
this demo manual to properly use or modify DC2257A.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2257A

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DEMO MANUAL DC2257A
QUICK START PROCEDURE
PARAMETER CONDITIONS MIN TYP MAX
Minimum Input Voltage, VPVIN 6V
Maximum Input Voltage – Switching, VPVIN 27V
Maximum Input Voltage – Not Switching, VPVIN VOVLO ≥ 1.25 38V
Maximum LED Voltage, VLED 35V
LED Current, ILED R5 = 100k, R6 = 73.2k 1.2A
Input Turn-On Voltage, VPVIN(EN) R7 = 19.1k, R8 = 1M, R9 = 93.1k, VPVIN Rising 5.9V
Input Turn-Off Voltage, VPVIN(UVLO) R7 = 19.1k, R8 =1M, R9 = 93.1k, VPVIN Falling 4.9V
Input OVLO Turn-Off Voltage, VPVIN(OVLO_TURN-OFF) R7 = 19.1k, R8 = 1M, R9 = 93.1k, VPVIN Rising 29.1V
Input OVLO Turn-On Voltage, VPVIN(OVLO_TURN-ON) R7 = 19.1k, R8 = 1M, R9 = 93.1k, VPVIN Falling 28.4V
Efficiency VPVIN = 12V, VLED = 35V, ILED = 1.2A 92%
Switching Frequency R1 = 23.2k, Spread Spectrum = OFF 350kHz
Input Current Limit RS1 = 0.008Ω 7.5A Peak
PERFORMANCE SUMMARY
Specifications are at TA= 25°C
To use DC2257A to evaluate the performance of the
LTM8005, refer to Figure 1 for the proper measurement
equipment setup and then 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 source or
connect the PWM pin to VREF on the PCB using R18.
1. Connect a string of LEDs with a forward voltage of 35V
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 ground with a
clip-onlead.
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 of greater than 29V.
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.

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DEMO MANUAL DC2257A
Figure 1. Proper Measurement Equipment Setup
QUICK START PROCEDURE

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DEMO MANUAL DC2257A
Figure 2. Output Current Noise Spectrum with Spread Spectrum = OFF, VIN = 12V, POUT = 42W, CT-1 Current Transformer
Figure 3. Output Current Noise Spectrum with Spread Spectrum = ON, VIN = 12V, POUT = 42W, CT-1 Current Transformer
QUICK START PROCEDURE
DETECTOR = PEAK–HOLD
RBW = 9kHz
CT–1 CURRENT TRANSFORMER
SPREAD SPECTRUM = OFF
FREQUENCY (MHz)
0
5
10
15
20
25
30
–50
–40
–30
–20
–10
0
10
20
30
40
50
AMPLITUDE (dBµV)
Output Current Noise Spectrum
DC2257A F02
DETECTOR = PEAK–HOLD
RBW = 9kHz
CT–1 CURRENT TRANSFORMER
SPREAD SPECTRUM = ON
FREQUENCY (MHz)
0
5
10
15
20
25
30
–50
–40
–30
–20
–10
0
10
20
30
40
50
AMPLITUDE (dBµV)
DC2257A F02

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DEMO MANUAL DC2257A
PARTS LIST
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 1 C1 CAP., X7R, 1μF, 50V, 10%, 0805 MURATA, GRM21BR71H105KA12L
2 5 C2, C3, C4, C7, C8 CAP., X7R, 4.7μF, 50V, 10%, 1210 MURATA, GRM32ER71H475KA88L
3 1 C5 CAP., X7R, 0.022μF, 16V, 10%, 0603 MURATA, GRM188R71C223KA01D
4 1 C6 CAP., X7R, 0.1μF, 25V, 10%, 0603 AVX, 06033C104KAT2A
5 1 L1 INDUCTOR, 10μH COILCRAFT, XAL8080-103ME
6 1 R1 RES, CHIP, 23.2k, 1/10W, 1%, 0603 VISHAY, CRCW060323K2FKEA
7 1 R2 RES, CHIP, 12.4k, 1/10W, 1%, 0603 VISHAY, CRCW060312K4FKEA
8 1 R3 RES, CHIP, 1.5k, 1/10W, 5%, 0603 VISHAY, CRCW06031K50JNEA
9 1 R4 RES, CHIP, 374k, 1/10W, 1%, 0603 VISHAY, CRCW0603374KFKEA
10 1 R5 RES, CHIP, 100k, 1/10W, 1%, 0603 VISHAY, CRCW0603100KFKEA
11 1 R6 RES, CHIP, 73.2k, 1/10W, 1%, 0603 VISHAY, CRCW060373K2FKEA
12 1 U1 I.C., μMODULE LED DRIVER, 80-BGA LINEAR TECH, LTM8005EY#PBF
Optional Demo Circuit Components
1 1 C13 CAP., X7R, 0.1μF, 25V, 10%, 0603 AVX, 06033C104KAT2A
2 0 C11, C19, C27 (OPT) CAP., 0603
3 0 C9, C10, C12, C15-C18, C22-C26 (OPT) CAP., 1210
4 1 C14 CAP., X7R, 6.8nF, 16V, 10%, 0603 AVX, 0603YC682KAT2A
5 0 C21 (OPT) CAP., ALUM, OPT, 10mm DIA.
6 1 D1 DIODE, SMA FAIRCHILD SEMI.,ES1A
7 0 L2 (OPT) INDUCTOR, OPT, 8mm × 8mm
8 0 M1 (OPT) MOSFET, SOT23
9 0 Q1 (OPT) TRANS, SOT23
10 1 RS1 RES, CHIP, .008Ω, 1W, 1%, 2512 VISHAY, WSL25128L000FEA
11 0 RS2 (OPT) RES, 2010
12 1 R7 RES, CHIP, 19.1k, 1/10W, 1%, 0603 VISHAY, CRCW060319K1FKEA
13 1 R8 RES, CHIP, 1M, 1/10W, 1%, 0603 VISHAY, CRCW06031M00FKEA
14 1 R9 RES, CHIP, 93.1k, 1/10W, 1%, 0603 VISHAY, CRCW060393K1FKEA
15 0 R10, R12-R15, R18, R19, R21-R27, R30 (OPT) RES, 0603
16 1 R11 RES, CHIP, 0, 1/10W, 1%, 0603 VISHAY, CRCW06030000Z0EA
17 1 R16 RES, CHIP, 0, 1/4W, 1%, 1206 VISHAY, CRCW12060000Z0EAHP
18 0 R20 (OPT) RES, 1206
19 3 R17, R28, R29 RES, CHIP, 100k, 1/10W, 5%, 0603 VISHAY, CRCW0603100KJNEA
Hardware
1 19 E1-E19 TESTPOINT, TURRET, .094" PBF MILL-MAX, 2501-2-00-80-00-00-07-0
2 1 JP1 HEADER 3-PIN 0.079 SINGLE ROW WURTH, 620 003 111 21
3 1 XJP1 SHUNT, .079" CENTER WURTH, 608 002 134 21

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DEMO MANUAL DC2257A
NOTE: UNLESS OTHERWISE SPECIFIED. 1. ALL RESISTORS 5%, 0603. 2. ALL CAPACITORS 0603.
SPREAD SPECTRUM
PVIN
VOUTPVIN
IVINN
VOUT
ISN
EN/UVLO
VIN
VREF
CTRL1 CTRL2
PWM
SW
/OPENLED
OVLO
FB
R7
19.1k
1%
LTM8005EY
U1
VIN
F1
EN/UVLO
G1
ISMON
J1
VREF
J6
PWM
J7
RAMP
J8
CTRL1
K6
CTRL2
K7
DA A5 DA A6
VOUT A7 VOUT A8
DA B5 DA B6
VOUT B7 VOUT B8
DA C5 DA C6
VOUT C7 VOUT C8
ISN F6 ISN F7 ISN F8
LED+ G6 LED+ G7 LED+ G8
IVINCOMP H2
SHORTLED H7
OPENLED H8
AUX J2
FB K2
VC K3
SW A1
SW A2
SW A3
SW A4
SW B1
SW B2
SW B3
SW B4
SW C1
SW C2
SW C3
SW C4
IVINN F2
IVINP G2
OVLO H1
GND
D1
GND
D2
GND
D3
GND
D4
GND
D5
GND
D6
GND
D7
GND
D8
GND
E1
GND
E2
GND
E3
GND
E4
GND
E5
GND
E6
GND
E7
GND
E8
GND
F3
GND
F4
GND
F5
GND
G3
GND
G4
GND
G5
GND
H3
GND
H4
GND
H5
GND
H6
GND
J3
GND
J4
GND
J5
GND
K1
SS
K4
RT
K5
GND
K8
R5
100k
1%
C7
4.7uF 50V 1210
C6
0.1uF
R29 100k
E14
GND
R12
(OPT)
E11
VOUT
C12
(OPT)
1210
C11 (OPT)
R3 1.5k
E10
GND
R11
0 Ohm
C8
4.7uF 50V 1210
C4
4.7uF 50V 1210
RS1
0.008
1%
2512
E4
GND
C1 1uF 50V 0805
E6
CTRL2
E2
PVIN 6V - 27V 38V MAX. 29V OVLO
E18
GND
E5
CTRL1
R1
23.2k 1%
350kHz
C3
4.7uF 50V
1210
E17
OPENLED
E19
V_EXT
R2
12.4k
1%
R17 100k
C13 0.1uF
E15
IVINCOMP
L1
10uH
COILCRAFT
XAL8080-103ME
E3
VIN 6V - 27V 38V MAX. 29V OVLO
R4
374k
1%
E8
ISMON
JP1
ON
OFF
1 3 2
R6
73.2k
1%
C10
(OPT) 1210
E1
EN/UVLO
C5 22nF
D1 ES1A
C2
4.7uF 50V
1210
E7
PWM
E13
GND
E9
GND
C14 6.8nF
E16
SHORTLED
R9
93.1k 1%
R22
(OPT)
R28 100k
C19
(OPT)
R8 1M 1%
E12 LED+
1.2A
35V LED MAX.
R16
0 Ohm
1206
C9
(OPT)
1210
SCHEMATIC DIAGRAM

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DEMO MANUAL DC2257A
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
VOUT PVIN
VOUT
VOUT
PVIN
PVIN
PVIN
VOUT
VOUT
VREF
VREF
VIN
CTRL1
PWM
FB
/OPENLED
SW
EN/UVLO
OVLO
ISN
C17
(OPT)
1210
R26 (OPT)
C26
(OPT)
1210
R27
(OPT)
C18
(OPT)
1210
C23
(OPT)
1210
C25
(OPT)
1210
Q1
SOT23
(OPT)
R24
(OPT)
R19 (OPT)
C16
(OPT)
1210
C24
(OPT)
1210
RS2
(OPT)
2010
C22
(OPT)
1210
R25
(OPT)
R23
(OPT)
C15
(OPT)
1210
C27
(OPT)
R13 (OPT)
M1
(OPT)
SOT23
R21
(OPT)
L2
(OPT)
8mm x 8mm
+
C21
10mmDia.SMD
(OPT)
R18 (OPT)
R10
(OPT)
R14 (OPT)
R15 (OPT)
R30
(OPT)
R20
1206
(OPT)

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DEMO MANUAL DC2257A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] ●FAX: [phone] ●www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2016
LT 1016 • 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
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ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.
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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.
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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.
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