Step-down converter with linear bypass supports multimode PAs in mobile handsets

February 18, 2011 // By Paul Buckley
Maxim Integrated Products has introduced a step-down converter designed to power PA (power amplifier) modules in mobile phones. The company claims the MAX8989 is first DC-DC converter in the industry to support power management for multiple communication protocols (e.g., LTE, WCDMA, GSM, and EDGE).

The device is ideal for converged (multimode) PAs which is a solution utilized in Infineon’s proven SMARTi UE2 RF engine platform, which delivers unparalleled flexibility and efficiency to multistandard cellular phone systems.

The MAX8989 integrates a high-efficiency switching regulator with a parallel bypass LDO to guarantee maximum efficiency under all conditions. The approach enables designers to minimize the amount of power dissipated within the PA by regulating the PA’s output stage supply voltage. By controlling the PA supply voltage to meet transmission-power requirements, designers can extend 2G talk time by up to 25% and 3G talk time by up to 10%.

The integrated LDO serves to smooth the transition between step-down regulation and operation in dropout, allowing for a seamless transition to higher power levels. When in dropout, the LDO becomes a low-impedance (85 milliohm) bypass FET to ensure minimal power loss during periods of peak current demand. Additionally, the switching regulator is capable of a 100% duty cycle to further eliminate losses.

The MAX8989 supports up to 2.5 A, making it an excellent choice for powering GSM/EDGE PAs. The device is fully specified over the -40 to +85 degrees Celsius extended temperature range, and offered in a compact (1.6 mm × 1.6 mm, 0.69 mm max height), 9-bump wafer-level package (WLP). Prices start at $1.92 (1000-up, FOB USA). Samples and evaluation kits are available upon request.

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