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dc1831af

DEMO MANUAL DC1831A

DESCRIPTION

LT3763

High Power Constant Current,

Constant Voltage Synchronous

Buck Controller

Demonstration circuit 1831A is a high power constant

current, constant voltage synchronous buck controller

up to 60V. The output is optimized for 10V, 10A as a

LED driver. As an LED driver, the output current is being

regulated until the output voltage reaches a programmed

voltage limit. The voltage limit on the demo board is set to

around 15V by R11 and R14. The load to be used with this

demo board is high current LEDs or laser diodes. Smaller

LEDs may not be able to handle the high current, even for

a short period of time. It is necessary to mount the LED

load on a proper heat sink. A fan may become necessary

to avoid exceeding LED’s maximum temperature rating.

The input voltage range of the LT3763 itself is 6V to 60V.

The demo board input range is 12V to 60V, therefore, the

demo board utilizes 80V MOSFETs. If an application has

a maximum input voltage of 48V, 60V MOSFETs such as

BSC100N06LS3, can be used for better efficiency at lower

voltage range. The typical efficiency of the demo board is

95% from a 24V input to a 10V, 10A load. The lower the

input voltage, the higher the efficiency tends to be for a given

load. At an output power level of 100W, even a one percent

efficiency improvement is a big 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. The LT3763 turns off unnecessary circuits during

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

efficiency in many PWM dimming applications is high.

In most applications, input voltage reaching the maximum

specification is a transient event. However, a fan helps the

circuit to stay cool if running at or near peak input voltage

at full load in steady state. If running in steady state at

or near maximum input voltage and full load is required,

please contact LTC applications engineering.

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.

The demo circuit 1831A achieves fast current rise time

from 0A to 10A. To see the real rise time, connecting wires

between the LED and the board should be as short as

possible to minimize the wire inductance and resistance.

The cathode of the LED should return to LED– with R17

populated with a resistor in a few mΩ. It is recommended

to measure the voltage on R17 with a short 50Ω coax cable

directly into a BNC connector on the oscilloscope. The

current can be calculated from the measured voltage. A

current probe adds more delays to the rise time so using

a current probe is not recommended. If fast rise time is

not required, the cathode of the LED can be connected to

GND as shown in Figure 2.

The LT3763 data sheet gives a complete description of

the part, operation and application information. The data

sheet must be read in conjunction with this quick start

guide for demo circuit 1831A.

Design files for this circuit board are available at

http://www.linear.com/demo

10

96

98

100

50

DN1831A F01

94

92

95

97

99

93

91

90

20

30

40

60

LED CURRENT = 5A

LED CURRENT = 10A

Figure 1. Demo Board Efficiency