Analog Devices have introduced the LT3950 multi-topology LED Driver designed specifically to drive high current LEDs. The device contains a DMOS switch with 1.5A peak current @ 60V and can support an external PWM dimming PMOS. The LT3950 device also features spread spectrum frequency modulation (SSFM) and a well-controlled switch node for low emissions.
The LT3950 has an internal PWM generator for dimming that maps an analog control signal to an exponential scale used to define PWM dimming duty ratio. Using this exponential scale approach, allows the device to define the duty ratio preserving dimming resolution across a wide range of LED currents. In addition to operating as a constant current source, the LT3950 also has provision for output voltage regulation, this feature can be used to protect the device against damage in the case of an open circuit LED event.
Application Circuit
The LT3950 has a programmable switching frequency from 300kHz to 2MHz, this offers design flexibility allowing configuration for higher efficiency or reduced component size. The integrated high-side PWM-dimming MOSFET makes this a very versatile IC, it can be used for boost, buck-boost mode and buck mode LED driver applications. The integrated MOSFET not only provides high PWM dimming ratio capability, but it also serves as a short-circuit protection device, the device also has a FAULT flag to indicate when there is either a short-circuit or open-LED fault at the output.
The device also permits use of spread spectrum frequency modulation, reducing EMI and enabling designs to meet the CISPR25 Class 5 standard. Furthermore, the switching frequency can also easily be synchronized by driving the SYNC/SPRD pin with an external clock.
Efficiency and Power Loss Performance Graph
The desired output LED current can be programmed using a single external sense resistor and can be adjusted from zero to full-scale by an analog signal at the CTRL pin allowing ease of control.
High voltage operation, 3V input voltage operation, multiple topologies, small-and-compact size, fault protection, low EMI, and multiple brightness control options make the LT3950 flexible and powerful for compact, noise-sensitive LED driver solutions. The device is supplied in a compact 16 lead MSOP package and is offered in a choice of operating temperature ranges, -40°C to +125°C (LT3950E) and -40°C to 150°C (LT3950J).
Evaluation Board
The LT3950 LED Driver is supported by demonstration circuit DC2788A, this demonstration circuit can be used to drive a string of up to 28V of LEDs at 330mA. DC2788A runs from an input voltage range of 6V to 24V at 2MHz and has the capability to turn on spread spectrum frequency modulation (SSFM) for a frequency range of 2.0MHz to 2.5MHz. Dimming control can be achieved with analog dimming or PWM dimming—either from an external or internally-generated clock source. DC2788A features undervoltage lockout (UVLO) set at 6.6V with a 1.0V hysteresis for turn-on.
The UVLO voltage, LED current, output voltage range, switching frequency, brightness control, SSFM, and the topology can all be adjusted with simple modifications to the demonstration circuit. The demo circuit is designed to be easily reconfigured to suit other applications, including the example schematics in the data sheet. Please read the LT3950 data sheet in conjunction with this demo boards manual to properly use or modify demo circuit DC2788A.
FREE samples for UK and Ireland customers only, subject to availability.
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