Part # Application Notes Power Supply And Power Management L4971 L6902 L6920 STEVAL-ILL008V1 AN1941 datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics

Part Description: Low Voltage LED Driver Using L6920D, L4971 and L6902D

Part Details:

AN1941 APPLICATION NOTE LOW VOLTAGE LED DRIVER USING L6920D, L4971 AND L6902D 1 INTRODUCTIONHigh brightness LEDs are becoming a prominent source of light and often have better efficien-cy and reliability when compared to that of conventional light sources. While LEDs can oper-ate from an energy source as simple as a battery and resistor, most applications require anefficient energy source not only for the reduction of losses, but also for the lumen maintenanceof the LED itself. STMicroelectronics has developed the following non-isolated DC-DC con-stant current LED driver to aid designers in developing a low cost and efficient platform for driv-ing high brightness LEDs.This application note will cover 3 DC-DC power supplies to drive high intensity LEDs. 1 The L6920D boost converter to drive 1 LED for a flash light application2 The L4971 buck converter to drive 1 to 9 LEDs3 The L6902D buck converter to drive 1 to 6 LEDs Figure 1. Reference Design Boards: L6920D L4971 L6902D AN1941/0604 1/15 AN1941 APPLICATION NOTE 2 L6920D LED DRIVERWhite LEDs are gaining popularity as sources of illumination because of their high efficiencyand reliability. Typical forward voltage drop of a white LED is approximately 3.5V. When theseLEDs are powered from a single or two cell batteries, a boost converter is needed to boost thevoltage to drive the LEDs. 2.1 L6920D DescriptionL6920D is a high efficiency step-up converter requiring very few external components to real-ize the conversion from the battery voltage to the selected output voltage or current. The start-up is guaranteed at 1V and the device is operating down to 0.6V. The device has very low qui-escent current, only 10µA. Internal synchronous rectifier is implemented with a 120m P-channel MOSFET, replacing the conventional boost diode, to improve the efficiency. This alsoimplies a reduced cost in the application since no external diode required.Following is the block diagram of L6920D. Figure 2. Block diagram of L6920D OUT VOUT ZERO CROSSING - - V + REF - + + VBG SHDN FB Y VOUT VOUT A GND B LX VIN R C A 1,R2 Y OPAMP B - (CR) C + VBG GND Q Toff min - 1µsec

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Application Notes Power Supply And Power Management L4971 L6902 L6920 STEVAL-ILL008V1 AN1941.pdf Datasheet