Convertors cut handset power down to size

High-efficiency dual-output DC/DC boost convertors manage two sets of six white light emitting diodes - all from a single integrated circuit plus inductor.

Texas Instruments has introduced two new high-efficiency dual-output DC/DC boost convertors that can manage two sets of six white light emitting diodes (LEDs) - all from a single integrated circuit plus inductor.

The devices feature an input voltage of 3 to 6V and can deliver up to 0.7A of output current, making them well suited to drive organic LED (OLED) subdisplays and white LED backlighting for the liquid crystal display (LCD) main display in today's clamshell phones.

TI's TPS61140 device allows a portable electronics designer 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 them on separately or simultaneously.

If the TPS61140's voltage output is enabled, the boost convertor is controlled by pulse frequency modulation (PFM) to achieve high efficiency over a wide load range.

If the current output is selected, the device adopts a 1.2MHz pulse width modulation (PWM) control method to maximise output current.

Applying an external PWM signal to the select pin reduces the output current, thereby allowing white LED dimming.

TI's new TPS61150 high-frequency boost convertor with two regulated current outputs drives white LEDs in LCD backlights for the sub and main displays in clamshell phones.

As with the TPS61140, this device's output current can be reduced by implementing a PWM signal on the select pins or an analogue voltage on the ISET pin, resulting in PWM dimming of the white LEDs.

The TPS61150 regulator's 1.2MHz fixed switching frequency reduces output ripple and avoids audible noises 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.

The TPS61140 and TPS61150 eliminate the need for any external active power components, while maintaining a high degree of efficiency and design flexibility.

The devices incorporate a power MOSFET and power diode.

In addition, the high switching frequency reduces the sise requirements of the external inductor and capacitor.

The TPS61140 and TPS61150 are available in volume production from TI and its authorised distributors.

The devices come in tiny 10-pin 3 x 3mm QFN packages, and are priced at $1.85 for the TPS61140 and $1.65 for the TPS61150 in quantities of 1000 units.

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