Power Converter Boosts Handset Battery Life

Oct 3, 2006 3:21 PM

The SC250 and SC251from Semtech are the first members of a dc-dc stepdown (buck) power converter family designed to improve battery life by providing adaptive dc power control in CDMA and WCDMA handsets. CDMA and WCDMA handsets experience wide swings in power consumption based upon their distance from a base station. The SC250 and SC251 are designed to work with the phone’s baseband processor to enhance the phone’s efficiency by adaptively controlling the dc power supply to the power amplifier (PA).

The SC250 performs a buck conversion to generate an output voltage that is linearly proportional to an analog input control voltage from the baseband processor. The buck conversion process reduces battery current when the PA outputs low power, greatly increasing talk time compared to directly connecting the PA to the battery.

The SC251 performs a similar function, but it utilizes a proprietary nonlinear transfer function that can eliminate the need for a software look-up table. The nonlinear transfer function is matched to the power requirements of certain CDMA and WCDMA PAs, reducing the need for software development and optimizing talk time. In addition, the SC251 provides the option to switch between two different transfer functions when used with a dual-mode PA. Each transfer function is optimized to match the dc power requirements of the different PA gain modes.

The adaptive buck converter starts up and responds to changes in requested output voltage in less than 40 µs. For increased efficiency at maximum transmit power, the devices feature a pass-through mode where an integrated switch connects directly between the battery and the output, bypassing the inductor. The SC250 has a 75-mΩ switch, and the SC251 a 200-mΩ switch, with a pin for driving an optional external FET when ultra-low series resistance is required.

The SC250 is rated for a maximum average current of 600 mA and an output range of 0.3 V to 3.6 V, while the SC251 is rated for a maximum average current of 800 mA and an output range of 0.5 V to 3.3 V. Both devices are rated for input voltages between 2.7 V and 5.0 V.

The SC250 features a 2.3-mm x 2.3-mm MLPD-W8 package with a maximum profile of just 0.8 mm. The SC251 comes in a 3-mm x 3-mm MLPD-10 package. Both devices are RoHS and WEEE compliant. The SC250 is priced at $1.36 each, and the SC251 is priced at $1.38 each, both for 1000-piece lots.