Linear Technology's dual-channel boost LT3486 can drive 16 white LEDs (8 serial LEDs per channel) at a constant current. In addition to providing PWM dimming, it also maintains the LED's fixed illumination color. It is suitable for applications such as portable electronic devices and automotive display screen backlights.
Features of the LT3486
• Wide (1000:1) dimming range • Independent dimming and shutdown control for LED drivers • Drive up to 16 white LEDs from a single-cell Li-Ion battery at 25mA (8 per drive)
• Drive up to 16 white LEDs from a 12V supply at 100mA (8 per drive)
• ±3% LED current programming accuracy • LED open circuit protection: 36V clamp voltage • Fixed frequency operation: up to 2MHz
• Wide input voltage range: 2.5V to 24V
• Available in (5mm x 3mm x 0.75mm) 16-pin DFN and 16-pin TSSOP packages
LT3486 application
The LT3486's switching frequency can be set from 200kHz to 2MHz with a single Resistor, allowing designers to minimize solution footprint and maximize efficiency. Because the LT3486 features a constant frequency architecture, it has the lowest noise and eliminates potential interference with any on-board RF or audio circuitry. Other features include internal soft-start/inrush current limiting and LED open-circuit protection. The LT3486's high efficiency, versatility, low noise and minimal "total solution" footprint make it ideal for a wide range of applications requiring a lot of white LED backlighting in space-constrained form factors.
The circuit diagram of 16 white LEDs driven by 12V input voltage is as follows:
12V input voltage drive 16 white LED circuit diagram
PWM dimming control requires an external NMOS Transistor to the last LED cathode of a string of white LEDs, as shown in the figure above. When PWM is high, these series LEDs are connected to the RFB resistor, the series white LED is lit, the current ILED = 200mV/RFB; if the PWM is low, the series LED is off and the white LED does not emit light.
to sum up
The LT3486's high efficiency, current mode and fixed frequency operation ensure consistent LED brightness, low noise and longest battery life. Its two independent converters are capable of driving asymmetric LED strings (up to eight in series per converter) with an input voltage of 2.5V to 24V, with an efficiency of up to 85%. Its package and tiny external components provide a very compact footprint for space-constrained handheld applications. Its input voltage range allows it to be used in a variety of applications from lithium-ion battery powered handheld products to automotive backlighting applications. (Edit: Technology)
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