The LM3269 buck-boost dc-dc converter from Texas Instruments improves the efficiency of power amplifiers (PAs) in mobile devices. It cuts power consumption by as much as 50%, improving battery life and decreasing heat generation in the PAs. Also its optimized output power produces higher upload throughput rates in 3G or 4G LTE.

1. With the battery powering the PA directly, efficiency is low meaning significant waste of power and extra heat dissipation.

Previously, the PA was one of the biggest power hogs in mobile devices, like cell phones, tablets, and data cards. To get the linearity needed for 3G and 4G LTE operation, PAs operate in class A or AB, which is quite inefficient. Figure 1 shows the traditional approach with the battery directly powering the PA. With this arrangement, the amount of power wasted is significant.

2. Using the LM3269 from Texas Instruments buck-boost converter to power the PA, output voltage is adjusted to maximize power output but reduce wasted power. The control input comes from a signal in the transmit signal chain derived from RF power output feedback.

The power inefficiency is based on the power levels used, so the battery drives the LM3269. Figure 2 shows the product’s approach, where the output is optimized for a given desired power output level and the energy wasted is significantly minimized.

The switch-mode buck-boost dc-dc converter can output a dc supply voltage to the PA, which is below or above the input battery voltage. The adjustment in output is automatic and rapid with changes occurring in microseconds. The battery voltage can range from 2.7 to 5.5 V and the output voltage range is 0.6 to 3.8 V. The device has a switching frequency of 2.4 MHz and delivers up to 95% efficiency. Maximum load capacity is 750 mA, meaning it can supply multiple PAs. It comes in a 2- by 2- by 0.6-mm 12-bump microSMD package and sells for $1.20 in 1000-unit quantities.

Texas Instruments