Linear Technology DC2257A Demo Manual

DEMO MANUAL DC2257A

LTM8005

38V

DESCRIPTION

Demonstration circuit 2257A features the LTM®8005 – a

, 38V

38V

IN

connect the output to protect against faults and provides
spread spectrum switching to simplify emissions compli­ance. DC2257A is an LED driver with an input range for
normal operation from 6V to 27V. 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

boost μModule® LED driver that can dis-

OUT

, 38V

IN

OUT

Boost µModule

LED Driver with 40V Switch

modulation rate including disable, feedback loop com­pensation, EN/UVLO threshold, OVLO threshold, soft­start 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

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

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1

DEMO MANUAL DC2257A

PERFORMANCE SUMMARY

PARAMETER CONDITIONS MIN TYP MAX

Minimum Input Voltage, V

Maximum Input Voltage – Switching, V

Maximum Input Voltage – Not Switching, V

Maximum LED Voltage, V

LED Current, I

Input Turn-On Voltage, V

Input Turn-Off Voltage, V

Input OVLO Turn-Off Voltage, V

Input OVLO Turn-On Voltage, V

Efficiency V

Switching Frequency R1 = 23.2k, Spread Spectrum = OFF 350kHz

Input Current Limit RS1 = 0.008Ω 7.5A Peak

LED

PVIN

LED

PVIN(EN)

PVIN(UVLO)

PVIN(OVLO_TURN-OFF)

PVIN(OVLO_TURN-ON

PVIN

PVIN

) R7 = 19.1k, R8 = 1M, R9 = 93.1k, V

Specifications are at TA = 25°C

27V

V

≥ 1.25 38V

OVLO

35V

R5 = 100k, R6 = 73.2k 1.2A

R7 = 19.1k, R8 = 1M, R9 = 93.1k, V

R7 = 19.1k, R8 =1M, R9 = 93.1k, V

R7 = 19.1k, R8 = 1M, R9 = 93.1k, V

PVIN

= 12V, V

LED

= 35V, I

= 1.2A 92%

LED

Rising 5.9V

PVIN

Falling 4.9V

PVIN

Rising 29.1V

PVIN

Falling 28.4V

PVIN

6V

QUICK START PROCEDURE

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.

supply voltage does not exceed the forward voltage of
the LED string. OVLO becomes active to inhibit switch­ing for an input voltage of greater than 29V.

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 V

on the PCB using R18.

REF

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

4. Connect an input to the PWM terminal. If PWM is not
used, connect PWM to a 2V to 5V DC source or to V

REF

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.

2

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QUICK START PROCEDURE

DEMO MANUAL DC2257A

Figure 1. Proper Measurement Equipment Setup

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3

DEMO MANUAL DC2257A

DETECTOR = PEAK–HOLD

RBW = 9kHz

CT–1 CURRENT TRANSFORMER

SPREAD SPECTRUM = OFF

FREQUENCY (MHz)

051015202530

–50

–40

–30

–20

–1001020304050

AMPLITUDE (dBµV)

Output Current Noise Spectrum

DC2257A F02

DETECTOR = PEAK–HOLD

RBW = 9kHz

CT–1 CURRENT TRANSFORMER

SPREAD SPECTRUM = ON

FREQUENCY (MHz)

051015202530

–50

–40

–30

–20

–1001020304050

AMPLITUDE (dBµV)

DC2257A F02

QUICK START PROCEDURE

Figure 2. Output Current Noise Spectrum with Spread Spectrum = OFF, VIN = 12V, P

Figure 3. Output Current Noise Spectrum with Spread Spectrum = ON, V

= 12V, P

IN

= 42W, CT-1 Current Transformer

OUT

= 42W, CT-1 Current Transformer

OUT

4

dc2257af

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

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

, 1%, 0603 VISHAY, CRCW060319K1FKEA

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5

DEMO MANUAL DC2257A

SCHEMATIC DIAGRAM

VOUT

E11

C19

(OPT)

VOUT

C10

(OPT)

1210

C8

4.7uF

50V

1210

C7

4.7uF

50V

1210

C4

4.7uF

50V

1210

E12 LED+

1.2A

35V LED MAX.

OPENLED

GND

GND

E14

E13

D1

ES1A

R2

12.4k

ISN

SHORTLED

IVINCOMP

E17

E15

E16

1%

FB

/OPENLED

R29

R28

C11

(OPT)

100k

100k

E19

V_EXT

E18

GND

VOUTPVIN

NOTE: UNLESS OTHERWISE SPECIFIED.

R12

(OPT)

R11

R81M1%

1. ALL RESISTORS 5%, 0603.

2. ALL CAPACITORS 0603.

R9

0 Ohm

IVINN

93.1k

L1

1%

SW

10uH

XAL8080-103ME

RS1

0.0081%2512

COILCRAFT

R7

19.1k

OVLO

C2

4.7uF

C3

4.7uF

C9

(OPT)

50V

50V

1%

1210

1210

1210

R4

1%

374k

A8

B8

VOUTA7VOUT

VOUTB7VOUT

C8

VOUTC7VOUT

ISNF6ISNF7ISN

A6

B6

C6

DAA5DA

DAB5DA

DAC5DA

SW

C4

SW

C3

SW

C2

SW

C1

SW

B4

SW

B3

SW

B2

SW

B1

SW

A4

SW

A3

SW

A2

SW

A1

F8

G8

LED+G6LED+G7LED+

J2

K2

H2

FB

AUX

IVINCOMP

H7

SHORTLED

H8

OPENLED

K3

VC

U1

IVINN

F2

IVINP

G2

OVLO

H1

VIN

EN/UVLO

F1

G1

VIN

EN/UVLO

VREF

J6

VREF

LTM8005EY

1%

R5

100k

R17

100k

CTRL1 CTRL2

CTRL1K6CTRL2

K7

ISMON

PWMJ7RAMP

J1

J8

C13

PWM

0.1uF

C5

1.5k

6.8nF

GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND

RT

SS

22nF

K8
K1
J5
J4
J3

H6
H5
H4
H3
G5
G4

G3
F5
F4
F3

E8

E7

E6

E5

E4

E3

E2

E1

D8

D7

D6

D5

D4

D3

D2

D1

R1

350kHz

23.2k

1%

K5

K4

C6

0.1uF

R22

(OPT)

132

JP1

ON

OFF

SPREAD SPECTRUM

R3

C14

PVIN

E1

EN/UVLO

E2

PVIN

6V - 27V

38V MAX.

29V OVLO

6

C12

(OPT)

1210

R16

0 Ohm

1206

C1

1uF

50V

0805

1%

R6

73.2k

E6

E8

E7

E3

VIN

6V - 27V

38V MAX.

E4

GND

29V OVLO

E5

CTRL1

CTRL2

PWM

ISMON

E10

E9

GND

GND

dc2257af

SCHEMATIC DIAGRAM

VOUT

DEMO MANUAL DC2257A

R26

(OPT)

R30

(OPT)

R21

IVINN

PVIN

(OPT)

R19

C15

C24

(OPT)

(OPT)

OVLO

1210

(OPT)

1210

C25

C16

(OPT)

1210

(OPT)

1210

C26

C17

(OPT)

1210

(OPT)

1210

VOUT

C18

RS2

SW

ISN

(OPT)

2010

(OPT)

1210

R23

R25

VREF

(OPT)

FB

(OPT)

Q1

(OPT)

SOT23

R24

(OPT)

M1

R27

(OPT)

(OPT)

VOUT PVIN

/OPENLED

SOT23

L2

(OPT)

8mm x 8mm

R10

(OPT)

PVIN

EN/UVLO

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.

C21

+

C23

C22

C27

(OPT)

10mmDia.SMD

(OPT)

(OPT)

(OPT)

1210

1210

VOUT

PVIN

VOUT

R14

R13

(OPT)

(OPT)

R20

VIN

1206

(OPT)

CTRL1

R15

(OPT)

R18

VREF

(OPT)

PWM

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7

DEMO MANUAL DC2257A

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

Linear Technology Corporation

8

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone] ● www.linear.com

dc2257af

LT 1016 • PRINTED IN USA

© LINEAR TECHNOLOGY CORPORATION 2016