Mobile device designers are facing changing standards and requirements to increase battery life and extend call and data transmission times. To help designers address these technical challenges, Fairchild Semiconductor (NYSE: FCS), a leading global provider of high-performance power and mobile solutions, has developed power management products for the RF domain of mobile terminals and tablets.

As part of its ongoing mobile initiative, Fairchild has developed the FAN5904 high-power, high-efficiency synchronous buck converter in close collaboration with customers to support GSM/GPRS/EDGE, 3G/3.5G, and 4G power amplifiers (PAs). The device reduces power consumption in wireless-enabled mobile devices, extending connection time by more than 60 minutes. The FAN5904 provides a compact solution footprint occupying less than 23.5 mm² and lowers operating temperatures by as much as 20ºC while maintaining the RF performance of the PA.

The FAN5904 supports high-power and low-power modes for GSM/EDGE PAMs, 3G/3.5G, and 4G PAs, respectively. In high-power mode, GSM Tx power is enabled, and the FAN5904 can provide up to 35dBm of output power even when a 3:1 VSWR antenna mismatch occurs for GSM/EDGE PAMs. The device operates in PWM mode under a 3MHz switching frequency condition, handling 2.3A and achieving up to 92% efficiency. For 3G/3.5G and 4G PAs, the FAN5904 operates in low-power mode and supports up to 29dBm of output power, including 3:1 VSWR conditions.

Under low-power mode conditions, the switching frequency of FAN5904 is 6MHz in PWM mode for heavier current loads. Under lighter current load conditions of 100mA or less, the FAN5904 switches to PFM mode to further optimize efficiency when the PA's output power is 20dBm. Since the FAN5904 operates at 3MHz in high-power mode and 6MHz in low-power mode, this can be implemented using one 470nH 2520 inductor and two 4.7µF 1508 capacitors, resulting in a PCB space of 20.5mm². For additional space savings, using a 470nH 2016 inductor allows the entire FAN5904 solution to be implemented in a space of less than 15mm².

The device's output voltage can be dynamically varied from 0.4V to 3.5V in proportion to the analog input VCON, which has a range of 0.16V to 1.40V provided by an external DAC. This allows the PA to be supplied with a voltage that supports maximum power addition efficiency. The FAN5904 also offers high-speed switching times, enabling the output voltage for power switching to be changed within 10µs. A current mode control loop, providing rapid transient response characteristics, ensures excellent line and load regulation capabilities.

The FAN5904 is available in a 1.71mm x 1.71mm WLCSP-16 package with a low profile and small form factor.

Fairchild Semiconductor is continuously developing innovative mobile designs through its diverse solutions that provide solutions to powerful design challenges, such as increased efficiency, reduced board space, signal fidelity protection, and design simplification. By integrating leading circuit technologies into ultra-small, advanced packaging, Fairchild reduces design size, cost, and power while providing benefits to mobile users. Fairchild engineers are working closely with leading mobile manufacturers to achieve faster time-to-market and improve performance in the next generation.