4W boost LED driver solution based on LT3519 efficiency 89%

As the number of medium power (1W to 4W) LED string applications increases, so does the need for compact, high efficiency, high performance LED drivers . The LT3519 LED driver meets a wide range of applications including LCD displays, automotive and avionics applications, architectural and industrial lighting , portable projection and scanners. Its 16-pin MSOP package includes precise LED current regulation, PWM and analog dimming for brightness control, and open-circuit protection with fault detection. The device also features small size and high efficiency.

The 400kHz LT3519 LED driver includes an integrated 750mA/45V peak power switch, compensation components, and a low-leakage Schottky diode for a simple, compact design. Despite its high level of integration, the device can be used in a variety of topologies, including boost, SEPIC, buck mode, or buck-boost mode. To maximize versatility, the anode of the Schottky diode (ANODE) ​​and the emitter (SW) pin of the internal power switch are individually pulled out so that the SEPIC coupling capacitor can be inserted between the two. The internal compensation component is selected to match the 2.2μF to 4.7μF output capacitance in the above topology. The integrated compensation network combined with current mode control produces a fast and stable transient response.

The device also includes OPEN LED detection and fault reporting. Use the resistor divider to set the overvoltage protection output voltage to prevent the LED string from opening. In the event of a fault, a small pull-up resistor can make the open collector OPEN LED output pin active.

4W boost LED driver

The simple step-up LED driver in Figure 1 drives up to 38V LEDs at 100mA over the automotive input voltage range. For automotive, avionics and industrial solutions, a 400kHz switching frequency is common. The driver combines high efficiency, small size inductors and capacitors with high PWM dimming capability while avoiding the frequency of the AM broadcast band. A small inductor with a rated saturation current of about 750 mA, several ceramic capacitors, and a few tiny resistors are all the components needed to complete the design. As shown in Figure 2, using the integrated LT3519PWM dimming architecture and an extremely low leakage integrated Schottky diode, the tiny PWM dimming MOSFET can be used to provide over 1000:1 PWM dimming at 120Hz.

At a frequency of 120 Hz, a 1000:1 dimming ratio is extremely high for a 400 kHz switching regulator. Since a higher switching frequency typically corresponds to a higher PWM dimming ratio, the dimming ratio can be further increased by selecting a higher frequency driver. In this case, avoiding the AM band means jumping to 2MHz, which reduces the maximum duty cycle and efficiency. The LT3519's 400kHz switching frequency does what the 2MHz converter can't do: the LT3519 delivers high duty cycle down to 6VIN at 38VLED and up to 89% efficiency at 12VIN. If PWM dimming is not required, MOSFET M1 can be removed and the analog dimming (CTRL) pin can be used to regulate the steady LED current to less than 100 mA for simple brightness control.

2.4W SEPIC LED Driver

The SEPIC topology is required when the voltage of the LED string is within the input rail voltage range. SEPIC produces a high PWM dimming ratio and also provides short-circuit protection. The SEPIC shown in Figure 3 drives the 16V LED at 150mA with an input range of 4V to 24V. Because the integrated clamp diode anode (ANODE) ​​is derived from a pin that is independent of the NPN power switch emitter (SW), the coupling capacitor is very easy to insert between the two. The highest voltage on the SW pin is slightly higher than the sum of the input voltage and the output voltage, so the 45V/750mA integrated power switch satisfies these specifications.

4W boost LED driver solution based on LT3519 efficiency 89%

Figure 14W boost LED driver with 89% efficiency at 12VIN

4W boost LED driver solution based on LT3519 efficiency 89%

Figure 2 integrated PWM dimming achieves 1000:1 dimming at 20Hz

4W boost LED driver solution based on LT3519 efficiency 89%

Figure 3 SEPICLED driver with short circuit protection

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