Flash LED drivers support camera flash and torch in smartphones

High-current stability can be assured in portable devices for dual- and quad-channel applications, using the AL3644 LED driver from Diodes.

The AL3644 high-speed, dual-channel flash LED driver is designed to support advanced camera flash and torch functionality in smartphones and other portable consumer devices. The driver includes independently controlled output currents configured through an I2C-compatible interface. It also has the ability to combine two devices (with different device identification addresses) to drive four LEDs up to 6A for quad-channel applications. The AL3644 is offered in chip-scale packaging and combines flexible switching-frequency capabilities with constant output current.

The AL3644 employs a constant-frequency, synchronous-boost, current-mode pulse width modulation (PWM) converter to deliver up to 1.5A for each of the two constant current sources across its 2.5 to 5.0V input voltage range. The I2C-compatible interface, operating at up to 400kHz, is used to configure the device to deliver a constant current at one of 128 levels between 1.4mA and 1.5A. The ratio between the two outputs is also adjustable through the I2C-compatible interface.

The AL3644 meets the need for sophisticated camera functionality, including video, with the convenience of a torch, increasingly specified in portable and wearable devices. The AL3544’s dual provides parallel current sources at efficiencies over 85 per cent in both torch mode and flash mode.

There are two switching-frequency options, 2.0 and 4.0MHz. The higher switching frequency also allows smaller passive components to be used, such as low-profile inductors and small 10 microF ceramic capacitors, reducing the overall bill of materials.

This is the first LED driver from Diodes to have an I2C-compatible interface. It also integrates a comparator that can be used with an external negative temperature co-efficient (NTC) to detect thermal variations. An input voltage monitor ensures the output current remains stable if, for example, the input voltage level drops as the device’s battery supply falls. Fault status bits, interrogated over the I2C-compatible interface, provide a host controller with operational data, such as flash current time-out, LED over-temperature, LED open/short failure, thermal shutdown, and input under-voltage.

The drivers are available in low torch current and high torch current variants in a U-WLB1713-12 package measuring 1.75 x 1.35mm.


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