OVERVIEW

The SM8135A is a charge pump type white LED driver. It can drive 1 to 4 backlight white LED connected in parallel, making it ideal for portable devices with small LCD. The charge pump switches between ×1 bypass mode, ×1.5 and ×2 boost mode in response to LED drive current requirements. The boost switching occurs in response to the drive current of all the connected LED and thus supports variations in LED forward-bias volt age drop (VF). Besides, the detection of switching is repeated in approx. 1sec-cycle by mode reset action, the SM8135A can respond to temporary variation of supply voltage. These ingenuities on switching detection can prolong the battery life to the fullest extent. Each LED drive current is controlled by a 4-channel LED drive

current control circuit. The LED drive current per channel is setup by external resistor. Moreover, the PWM signal control of EN pin can realize nonstep brightness control (10% to 100%). The IC ON/OFF is controlled by EN pin.

FEATURES

■ Battery life extension by automatic charge pump switch between ×1, ×1.5 and ×2 according to the detection of the LED drive current

■ Controlling 1 to 4 lights of white LED connected in parallel

■ Set up LED drive current value by external resistor (120kΩ: 20mA/ch)

■ 1-wire input controlling

■ ON/OFF and brightness control by PWM signal controlling of EN pin (10 to 100%)

■ Soft start circuit built-in

■ Thermal shut down circuit built-in

■ Input voltage range

    No-load current (IOUT= 0mA): 2.7 to 4.6V

    Load current (IOUT= 80mA): 3.0 to 4.6V

■ Maximum output voltage: 4.9V (typ)

■ Maximum output current: 80mA (typ)

■ Quiescent current

    Not-switching (×1 mode): 0.3mA (typ)

    Switching (×1.5 mode): 1.5mA (typ)

    Switching (×2 mode): 1.5mA (typ)

■ Standby current: 0.01µA (typ)

■ Operating frequency: 1MHz (typ)

■ LED drive current accuracy between channel

(REST = 120kΩ): ± 5% (max)

■ Package: 16-pin QFN



APPLICATIONS

■ Cellular phone

■ PDA

■ Portable games

■ Handy terminal

■ Digital still camera

■ Digital video camera

■ LCD panel back light

■ White LED driving