Dallas—Texas Instruments' TPS61140 and TPS61150 dual-output DC/DC boost converters can manage two sets of six white LEDs (two outputs, each up to 27 volts) for backlighting a clamshell phone's main LCD display. The TPS61140 is also suited to delivering up to 700 mA for organic LED (OLED) sub-displays.
The TPS61140, with one regulated voltage output and one regulated current output, allows designers to program each individual voltage and current level through external resistors. For additional flexibility, the designer can use each output’s dedicated selection pin to turn LEDs on separately or simultaneously. The chip uses pulse frequency modulation (PFM) control when operating in its voltage mode to maintain high efficiency over a wide load range. In current-mode operation, the device employs pulse width modulation (PWM) control. In this case, an external PWM signal can be applied to to the select pin to control output current, thus facilitating LED dimming.
The TPS61150 is a high-frequency boost converter with two regulated current outputs for driving white LEDs in LCD backlights for the portable device's sub and main displays. As with the TPS61140, the user can adjust output current for LED dimming by applying a PWM signal on the select pins or an analog voltage on the device's ISET pin. The TPS61150 regulator’s 1.2-MHz fixed switching frequency reduces output ripple and eliminates audible noise associated with PFM control. The device’s two outputs can also drive display and keypad backlights, together driving up to 12 white LEDs in one large display.
Click here for the TPS61140's datasheet and here for the TPS61150's. The TPS61140 is priced at $1.85 each, and the TPS61150 is $1.65, both in 1k quantities. Evaluation modules of both converters, application notes and TI’s newly updated Power Management Selection Guide are available through power.ti.com
Texas Instruments, 1-800-477-8924, www.ti.com