Powering radio frequency (RF) components in battery-powered applications is tricky because RF components are very sensitive to noise and interference. To handle this challenge, you might choose to power your RF applications with low-dropout regulators (LDOs) to filter noise. Sure, LDOs do a great job filtering, but they have low efficiency. DC/DC converters are more efficient, but they can be noisy. What if you could get the best of both worlds – the efficiency of a DC/DC converter without that nasty disruptive noise? It’s possible if you power your wireless microcontroller unit (MCU) or other RF component using an RF DC/DC converter.
RF DC/DC converters, such as the LM3281, implement a low-noise design inside of the chip. This buck converter provides up to 1.2A output current and a peak efficiency of 94%, while maintaining good enough noise performance (Figure 1) to power an RF component such as a Wi-Fi® or ZigBee® transceiver, Bluetooth® front-end modules (FEMs) and others.
The SimpleLink™ Wi-Fi CC3200 Internet-on-a-chip™ solution is a wireless MCU that has built-in power management that allows it to operate from a 2.1-3.6V input range. Above 3.6V, the CC3200 requires an external converter to lower the voltage into the operating range, while a small, low IQ solution, such as the LM3281, can transition from a 5V USB supply, a 4.5V lithium-ion battery or another voltage rail above 3.6V.
Figure 1: LM3281 displaying <10nV/√Hz noise (8.6974nV/√Hz) when measured with a signal analyzer
In many wireless designs, low or idle current is very important. For example, in IoT applications, such as connected home thermostats, wireless MCUs might operate in idle mode most of the time to conserve power, so idle current efficiency is critical. The LM3281 features 0.1µA IQ in disable mode and 16µA typical IQ. It is able to provide good efficiency by operating in economy mode (ECO) in low-current regions below 1mA, as shown in Figure 2. With the SimpleLink Wi-Fi CC3200, there is no need to be concerned about ripple in ECO mode, since it features internal filtering using LDOs to prevent any interference to RF operation.
Figure 2: LM3281 displaying 80-90% efficiency operating in ECO mode below 1mA IOUT with 3.8VIN
In what IoT or other wirelessly connected applications could you use a wireless MCU and RF DC/DC converter solution?
Additional resources:
- Read this applications note on powering low-power RF products.
- Check out basic questions regarding bucks and nominal voltage of batteries in this E2E Community™ post.
- Learn more about the LM3281 evaluation module.
- Review a TI Designs reference design for a low noise power supply for WLAN applications.
