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dc1470af

DEMO MANUAL DC1470A

DESCRIPTION

LT3743 High Current  

Synchronous Step-Down LED  

Driver with Three-State Control 

Demonstration circuit 1470A is a high current synchronous 

step-down LED driver with three-state control featuring 

the 

LT

®

3743EUFD

The demo board is optimized for 20A 

output from a 12V input. Being an LED driver, the output 

current is being regulated until the output voltage reaches 

a  programmed  voltage  limit.  This  voltage  limit  on  this 

demo board is set to around 6V by R5 and R6. The 6V is 

chosen because of the 6.3V voltage rating of the output 

capacitors. The ideal load to be used with this demo board 

is a single LED, such as PT120 from Luminus Devices. 

Smaller LEDs may not be able to handle the high current, 

even for a short period of time. At 20A, the demo circuit can 

operate continuously. However, it is necessary to mount 

the LED load on a proper heat sink and possibly with a 

fan to avoid exceeding its maximum temperate rating. 

Note: 

The  DC470A  will  drive  a  LED  with  its  cathode 

grounded. Grounding cathode of the LED allows customers 

to use positive input supply.
The input voltage range of the LT3743 itself is 6V to 36V. 

However, the demo board utilizes 30V MOSFETs to demon-

strate best efficiency so the maximum recommended input 

voltage is 24V for the demo board. When input is above 

20V during PWM dimming, a slightly larger inductance 

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.

PERFORMANCE SUMMARY

may be needed. The typical efficiency of the demo board 

is 94% from a 12V input to 5V, 20A load. The lower the 

input voltage, the higher the efficiency tends to be with 

a given load. At output power level of 100W, a couple of 

percent of efficiency improvement is a huge advantage in 

minimizing temperature rise. If an efficiency measurement 

is needed in an application, the output voltage must be 

measured at the output capacitors instead of at the LED 

load. This prevents cable loss from being counted as a 

loss of the board. If efficiency measurement is required 

during PWM dimming, the average current and voltage 

values should be measured with proper equipment. All 

LT3743 circuits turn off unnecessary circuits during PWM 

off period to minimize power losses. As a result, efficiency 

in many PWM dimming applications is almost the same 

as efficiency of the constant current applications.
The DC1470A uses a split output capacitor configuration 

to achieve <2μs current rise time from 0A to 20A. To see 

the real rise time, connecting wires between the LED and 

the board should be minimized to no more than 2 inches 

Specifications are at T

A

 = 25°C

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

PV

IN

*

Input Supply Range, P

VIN

 = V

IN

L1 is Optimized for 12V

12

26.4

V

V

OUT

*

Output Voltage

With One PT120 LED, 6V is the Over 

Voltage Limit

4.5

6

V

I

OUT

Output Current

CTRL_SEL > 1V

18.8

20

21.2

A

f

SW

Switching Frequency

400

430

460

kHz

I

RISE

Current Rise Time

Following a PWM Rising Edge

2

μs

EFF

Efficiency at DC

V

IN

 = 12V, V

OUT

 = 5V, I

OUT

 = 20A

94

%

*PV

IN

 and V

IN

 of the demo circuit are limited to 24V typical by the selection of MOSFETs. The LT3743 input range is 6V to 36V. V

OUT

 maximum of the 

demo circuit is limited to 6V due to the selection of the output capacitors.

Design  files  for  this  circuit  board  are  available  at  

http://www.linear.com/demo/DC1470A

Summary of Contents for DC1470A

Page 1: ... the demo board is 94 from a 12V input to 5V 20A load The lower the input voltage the higher the efficiency tends to be with a given load At output power level of 100W a couple of percent of efficiency improvement is a huge advantage in minimizingtemperaturerise Ifanefficiencymeasurement is needed in an application the output voltage must be measured at the output capacitors instead of at the LED ...

Page 2: ... have more noise but is ok for non critical measurements The LED connecting wires should be as short as possible 1 inch total being ideal 3 Turn on the power at the input R15 R16 and C15 help filtering out voltage spikes seen on the SENSE or SENSE pin It is critical to have those components on a board TheLT3743hasathree statecontrol Itcanchangeoutput current among zero a low level and a high level...

Page 3: ...3 dc1470af DEMO MANUAL DC1470A QUICK START PROCEDURE Figure 1 Proper Measurement Equipment Setup Figure 2 Measuring Voltage Across R25 IS IS ...

Page 4: ...INEON BSC080N03LS G 17 1 Q3 N CHANNEL MOSFET LFPAK INFINEON BSC011N03LSI 18 2 Q5 Q6 MOSFET 40V DUAL N CHANEL PPAK VISHAY Si7234DP 19 1 R1 RES CHIP 124k 1 1 W 0603 VISHAY CRCW0603124KFKEA 20 1 R2 RES CHIP 374k 1 1 W 0603 VISHAY CRCW0603374KFKEA 21 1 R3 RES CHIP 0 0025Ω 1W 1 2512 VISHAY WSL25122L500FEA 22 7 R4 R9 R10 R12 R13 R14 R20 RES CHIP 100k 1 1 W 0603 VISHAY CRCW0603100KFKEA 23 3 R5 R7 R8 RES ...

Page 5: ...UT MAY SIGNIFICANTLY AFFECT CIRCUIT PERFORMANCE OR RELIABILITY CONTACT LINEAR TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS SCHEMATIC 3 Friday July 31 2015 1 1 STEP DOWN LED DRIVER WITH THREE STATE CONTROL ANTONINA K WALKER B A LT3743EUFD DEMO CIRCUIT 1470A SIZE DATE IC NO REV SHEET OF TITLE CON...

Page 6: ...ORY 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...

Page 7: ...Mouser Electronics Authorized Distributor Click to View Pricing Inventory Delivery Lifecycle Information Analog Devices Inc DC1470A ...

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