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Demonstration circuit 2788A is a boost LED driver featuring the LT®3950. This demonstration circuit powers a string of LEDs at 330mA. The step-up topology can be used to drive a string of up to 28V of LEDs as assembled. The maximum output voltage capability of the LT3950 is 60V. DC2788A runs from an input voltage range of 6V to 24V as built. It also runs 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.
LT3950 is a monolithic 1.5A peak switch current, 60V LED driver. The guaranteed peak switch current rating of the IC is 1.5A and this is important to know when calculating maximum output current at a given LED voltage and input voltage for a boost converter. The LT3950 features SSFM and a well-controlled SW node for low emissions.
A frequency range of 200kHz to 2MHz and a high-side PWMTG PWM-dimming MOSFET makes this a very versatile IC for many applications. It can be used for boost, buck-boost mode and buck mode LED driver applications. The PWMTG MOSFET not only provides high PWM dimming ratio capability, but it also serves as a short-circuit protection device. The FAULT flag indicates when there is either a short-circuit or open-LED fault at the output.
The demo circuit is designed to be easily reconfigured to suit other applications, including the example schematics in the data sheet. Consult technical support for assistance.
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 LT3950JMSE featured on this demo circuit is available in a thermally enhanced 16-lead plastic MSOP package. The LT3950 data sheet must be read in conjunction with this demo manual to properly use or modify demo circuit DC2788A.