DC-DC converter circuit diagram for driving high current LED

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

The Linear Technology DC/DC Converter LT3955 features an internal 3.5A switch designed for use as a constant current source and constant voltage regulator. Available in a 5mm x 6mm QFN package, it offers a very compact, high power LED driver solution.

Linear Technology Corporation introduces the LT3955 DC/DC converter with an internal 3.5A switch designed for use as a constant current source and constant voltage regulator. The device's internal PWM dimming generator makes it ideal for driving high current LEDs, and it also has the ability to charge batteries and supercapacitors. The LT3955's 4.5V to 60V input voltage range is suitable for a wide range of applications including automotive, industrial and architectural lighting.

The LT3955 uses an internal 3.5A, 80V N-channel MOSFET capable of driving up to 12 300mA white LEDs with a nominal 12V input to deliver more than 20W. The device uses high-side current sensing and supports boost mode, buck mode, buck-boost mode, or SEPIC topology. In a boost topology, the LT3955 delivers greater than 94% efficiency, eliminating the need for an external heat sink. Its frequency adjustment pin allows the user to set the frequency between 100kHz and 1MHz, while optimizing efficiency while minimizing the size and cost of external components. The LT3955 is available in a 5mm x 6mm QFN package, providing a very compact, high power LED driver solution.

The LT3955 features an internal PWM generator with a dimming ratio of 25:1 and an external PWM signal for up to 3000:1 dimming ratio. For applications where dimming is not critical, a 10:1 analog dimming ratio can be provided via the CTRL pin. The device's fixed frequency, current mode architecture enables stable operation over a wide range of supply voltages and output voltages. Output short-circuit protection and open-circuit LED protection enhance system reliability. The LT pin of the LT3955 with reference to ground can be used as an input to multiple LED protection functions, so the converter can act as a constant voltage source in charging applications.

The LT3955EUHE is available in a 36-pin 5mm x 6mm QFN package and is priced at $3.75 each. The extended temperature version (Class I) LT3955IUHE is also available for $4.41 each. The above prices are in the unit price of 1,000 pieces, both of which are available from stock.



Performance Summary: LT3955

3000:1 True Color PWM dimming VIN range for LEDs: 4.5V to 60V
Rail-to-rail current detection range: 0V to 80V

Internal 80V/3.5A Switchable Programmable PWM Dimming Signal Generator Constant Current (±3%) and Constant Voltage (±2%) Regulation

Accurate analog dimming can drive LEDs in boost, SEPIC, CUK, buck mode, buck-boost mode, or flyback configuration
Output short circuit protection boost

Open circuit LED protection and reporting adjustable switching frequency: 100kHz to 1MHz
Programmable VIN undervoltage lockout (UVLO) with hysteresis

C/10 for battery charger indicates low shutdown current: <1μA
Thermally Enhanced 5mm x 6mm QFN-36 Package