At the medium-to-low end of the power spectrum there are modest power conversion requirements such as those commonly found in “Internet of Things” (IoT) equipment, which necessitate the use of power conversion ICs that deal with modest levels of current. These are usually in the range of 100’s milliamps of current, but can be higher if there are peak power demands that are needed by an onboard power amplifier for the transmission of data or video. Accordingly, the proliferation of wireless sensors supporting the numerous IoT devices has increased the demand for small, compact and efficient power converters tailored to space and thermal constrained device form factors.
However, unlike many other applications, many industrial and medical products typically have much higher standards for reliability, form factor and robustness. As you would expect, much of the design burden falls on the power system and its associated support components. Industrial, and even medical IoT products, must operate properly and switch seamlessly between a couple of power sources such as the AC mains outlet and a battery backup. Furthermore, great lengths must be taken to protect against faults, while also maximizing operating time when it is powered from batteries to ensure that normal system operation is reliable whichever power source is present. Accordingly, the internal power conversion architecture used within these systems need to be robust, compact and require minimal heat sinking.
Power Supply Design Considerations
It is not unusual for an industrial IoT system designer to use linear regulators in a system that incorporates wireless transmission capability. The primary reason being that it minimizes EMI and noise emissions. Nevertheless, although switching regulators generate more noise than linear regulators, their efficiency is far superior. Noise and EMI levels have proven to be manageable in many sensitive applications if the switcher behaves predictably. If a switching regulator switches at a constant frequency in normal mode, and the switching edges are clean and predictable with no overshoot or high frequency ringing, then EMI is minimized. Moreover, a small package size and high operating frequency can provide a small tight layout, which minimizes EMI radiation. Furthermore, if the regulator can be used with low ESR ceramic capacitors, both input and output voltage ripple can be minimized, which are additional sources of noise in the system.
It is common for the main input power to today’s industrial and medical IoT devices to be a 24V or 12V DC source from an external AC/DC adapter and /or battery bank. This voltage it then further reduced to either 5V and/or 3.xV rails using synchronous buck converters. Nevertheless, the number of internal post-regulated power rails in these medical IoT devices has increased while operating voltages have continued to decrease. Thus, many of these systems still require 3.xV, 2.xV or 1.xV rails for powering low power sensors, memory, microcontroller cores, I/O and logic circuitry. Nevertheless, the internal power amplifier used for data transmission can require a 12V rail with up to 0.8A of current capability to transmit any recorded data to a remote centralized hub.
Traditionally, this 12V rail has been supplied by step-up switching regulators, requiring specialized switch-mode power supply design know how, and needs a large solution footprint on the printed circuit board (PCB).