Adaptive Power Converter Family Boosts Battery Life in CDMA/WCDMA Phones

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. 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 patent-pending 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 40µs. 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 75mΩ switch, and the SC251 a 200mΩ 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 600mA and an output range of 0.3V to 3.6V, while the SC251 is rated for a maximum average current of 800mA and an output range of 0.5V to 3.3V. Both devices are rated for input voltages between 2.7V and 5.0V.

Both devices provide an on-board low-dropout voltage regulator (LDO) that provides a voltage bias that is required for operating a power amplifier, eliminating the need for an additional part. The SC250 and SC251 provide a regulated 2.85V, with the SC250 providing up to 20mA and the SC251 providing up to 10mA.

“These devices mark the launching of our new family of application specific buck regulators – targeted at improving power amplifier efficiency. PA current consumption is the biggest contributor to battery drain in a CDMA or WCDMA handset,” said Ven Shan, Vice President of Marketing for Semtech’s Power Management Group. “The true innovation of these devices lies in the adaptive nature of the power transfer scheme as well as the integrated PA biasing and their small size and low profile, which allow designers to add this functionality without impacting the size of their phones.”

The ultra small SC250 features a 2.3mm x 2.3mm MLPD-W8 package with a low profile of just 0.8 mm max. The SC251 comes in an industry-competitive 3mm x 3mm MLPD-10 package. Both devices are RoHS and WEEE compliant.

Both devices include a full range of protection features, including over current limit, thermal protection and undervoltage lockout - another benefit over straight battery-to-PA configurations.

The SC250 is available immediately in production quantities and is priced at $1.36 each in 1,000-piece lots. The SC251 is available immediately in production quantities and is priced at $1.38 each in 1,000-piece lots.