DC905A: 20mA @ 20.6V Max, 3 ~ 5V in, Boost


Demonstration circuit 905 is a LED Driver in SC70 with built-in Schottky featuring the LT3491. The LT3491 is a fixed frequency step-up current mode DC/DC converter.

There are two circuits on the demonstration board 905. The “small size” circuit generates 15mA LED current at the smallest possible solution size. The “high efficiency” circuit generates 20mA LED current at higher efficiency.

The circuit outputs share 6 LEDs. At any given time, depending on the positions of jumpers, only one circuit is in operation.

Other features of the LT3491, such as the internal Schottky diode, the high switching frequency and the internal open circuit protection, allow tiny components for both circuits.

The input range of the demo board is from 3V to 5V. Different dimming controls can be implemented on the demo board. Please refer to the quick start procedure. The high side current sensing feature of the LT3491 allows “one wire” current source, i.e. the low side of the LED string can return to ground anywhere.

The LT3491 datasheet gives a complete description of the part, operation, and application information. The datasheet must be read in conjunction with this quick start guide for working on or modifying demo circuit 905.


Manufacturer Linear Technology/Analog Devices
Category Lighting
Sub-Category LED Drivers - DC In
Eval Board Part Number DC905A-ND
Eval Board Supplier Linear Technology/Analog Devices
Eval Board Normally In Stock
Voltage In 3 ~ 5 V
Topology Step Up
Current Out 20 mA
Voltage Out (Max) 20.6 V
Outputs and Type 1 Non-Isolated
Efficiency @ Conditions >65%, 3.6 Vin, @ 5 ~ 20 mA (4 LEDs)
Features Current Limit (Adj. or Fixed)
Dimming Control
Open Circuit Protection
Shutdown, Enable, Standby
Switching Frequency 2.3 MHz
Component Count + Extras 21 + 8
Design Author Linear Technology
Application / Target Market Cellular Phone
Digital Cameras
MP3 Players
Portable Devices
Main I.C. Base Part LT3491
Date Created By Author 2005-04
Date Added To Library 2015-06

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