Understanding WLAN Thermal Issues

Understanding WLAN Thermal Issues

Wireless local area networks (WLAN) or Wi-Fi networks are systems in the home that manage information and data transfer, both locally and to the internet. We are now at the point where we expect our home security system, refrigerator, oven, HVAC, laptop, cell phone, and other household electronic equipment to not only talk to each other but converse with us. The trend today is to create smaller and lower power WLAN devices to handle all these entities. The WLANs are expanding by leaps and bounds in the household with a great deal of attention on tackling the distributed WLAN system's footprint and thermal problems. So, what does a WLAN thermal problem look like?

Smart controls for temperature, security, and sound rely on WLAN or Wi-Fi networks.

Some say that the power amplifier (PA), low-noise amplifiers (LNAs), and filters are the thermal (many times measured as Watts or power) eaters. Generally, these devices "eat" power or emit heat by running at faster data rates, creating linearity and accuracy re-transmit problems, or experiencing efficiency losses due to ambient temperature changes.    

These are legitimate problems, but the device that drives the power supply for all these functions also holds the highest position of prominence when it comes to the power and PCB “overeating” problem. The definitive combination of operational specifications for such a device are high efficiency and small size.

To solve these problems, I would start by examining traditional power-supply generation solutions. A simple LDO that down-converts the power-supply voltage is an excellent beginning. The LDO solution is the easiest to implement with a small-sized chip and a few resistors/capacitors, but its efficiency is dreadful. For a 24V to 5V LDO conversion, you will have a 21% efficiency rating. Additionally, high output currents demand bulky heatsinks which will send the small-sized LDO advantage down to the bottom of the list.    

A better approach is to use a step-down DC-DC switching regulator or buck converter. With a buck converter, a discrete inductor and switching strategy manages the conversion of our 24V to 5V power supply, with higher efficiency marks. This improves the efficiency of this power-supply solution from 21% to 80%.

The layout for a traditional buck converter consumes ~35.64mm2 of space (Figure 2). 

Traditional buck converter PCB layout (35.64mm2)

But, I did say that there is a discrete inductor involved, which consumes the PCB real estate. These devices need additional capacitors to fully implement power-supply conversion along with a degree of design engineering smarts to complete the switching regulator design’s component selection.  

The buck converter in Figure 1 tackles the LDO efficiency problem, but we are still battling the overall size issue because of the overbearing inductor’s size. We can do better.

Let's ratchet it up with a buck converter module. A buck converter module absorbs the inductor into the IC package, which theoretically reduces the PCB real estate even further. But to make this theory go to the next step, we need to select a buck converter module that utilizes a degree of packaging creativity.

Several buck modulator vendors have implemented the next step by stacking the built-in inductor on top of the integrated circuit (Figure 3).

Micro system-level IC packaging, as illustrated by the MAXM15462 uSLICTm power module, has inductor and buck converter IC stacking.

The power module in Figure 3 integrates the inductor and the buck converter in one simple compact package. In the finished package, the only external components needed are three capacitors and four resistors (Figure 4).

Inductor / IC circuit buck module brings the PCB layout to even smaller package dimensions; 2.6mm x 3mm x 15mm (W x L x H).

The buck module with inductor/IC circuit stacking dramatically reduces the PCB space occupied by the standard buck converter solution. The Figure 4 layout (27.93mm2) is 27% better than the traditional buck converter layout (35.64mm2).

Our distributed household WLAN systems continue to be used across the household landscape. One of the challenges in front of WLAN designers is to implement these systems with high power efficiency and low PCB real estate. A good starting point begins with a sound power-supply strategy and then moves on to the remaining components. We saw that a typical LDO solution falls short in terms of efficiency. The traditional IC switching buck converter falls short on size, design cycle time, and PCB area utilization. The package that stacks the IC and inductor in one package provides high efficiency and small size, bringing down the WLAN system’s temperature and size.