The SC250 and SC251 are the first members of a dc-to-dc step-down (buck) power converter family designed to improve battery life by providing adaptive dc power control. Developed by Semtech for CDMA and WCDMA handsets, the parts work with the baseband processor to enhance 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's 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, increasing talk time compared to directly connecting the PA to the battery.
The SC251 performs a similar function, but it uses a nonlinear transfer function that can eliminate 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 increasing 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 is rated for a maximum average current of 600 mA and an output range of 0.3 to 3.6 V, while the SC251 is rated for a maximum average current of 800 mA and an output range of 0.5 to 3.3 V. Both devices are rated for input voltages between 2.7 and 5.0 V. Both devices provide an on-board low-dropout voltage regulator (LDO) that provides a voltage bias that is required for operating a power amplifier.
The SC250 features a 2.3- by 2.3-mm MLPD-W8 package with a profile of 0.8 mm max. The SC251 comes in a 3- by 3-mm MLPD-10 package. Both devices are RoHS and WEEE compliant. The SC250 is available immediately in production quantities and is priced at $1.36 each in 1000-piece lots. The SC251 is available immediately in production quantities and is priced at $1.38 each in similar lots. More information is available at www.semtech.com.