May 21, 2019
| By: Anthony T. Huynh
Principal Member of the Technical Staff, Applications, Industrial Power, Maxim Integrated
From industrial internet of things (IIoT) to network infrastructure equipment, next-gen electronic systems are being infused with new intelligence that requires more power in ever-shrinking spaces without impacting the thermal budget. As a result, conventional solutions are not a good fit. Yet, given time-to-market pressures, designers don’t have loads of time to design the power supply, and they must wrestle with limited space to dissipate the heat while also meeting shock, vibration, and EMI requirements.
What’s the best way to power shrinking equipment and sensors reliably without overheating? And to create these power supply designs quickly?
Sensors have historically included a sensing element and some way to get the sensing data to the programmable logic controller (PLC). Data would be unidirectional and be transferred in analog format. Analog data communication, however, is prone to noise, and there isn’t a way for the controller to diagnose, re-configure, or recalibrate the sensor directly. Over time, the technology advanced, and sensor manufacturers began integrating more functionality into these devices while reducing noise susceptibility via binary sensors. In binary sensors, data is still limited to unidirectional communication, and a technician is still needed on the factory floor to handle tasks such as manual calibration.
Figure 1. Digital manufacturing environments rely on smart sensors for real-time insights.
The emergence of IO-Link is bringing intelligence to the edge of the factory floor by allowing bidirectional communication between sensors and the controller (Figure 2). With this capability, the system can adjust, configure, and diagnose sensors in real time—just what is needed to meet the demands of Industry 4.0 and smart factories.
Unlike traditional factories built and optimized for a single product, a smart factory is designed to adapt quickly to changes in market demands. Real-time diagnostic capabilities facilitate predictive maintenance and can boost factory uptime.
Figure 2. PLC with IO-Link Sensor
The intelligent features in smart sensors increase the power dissipation of these sensors. At the same time, there is a trend among industrial equipment manufacturers toward miniaturization. This means that powering smart sensors calls for addressing heat and size challenges. To illustrate the challenges, let’s consider a smart proximity sensor with IO-Link (Figure 3). In this application, a microcontroller collects data from the sensing element, linearizes and calibrates it, and sends it to the IO-Link transceiver. From here, the data is sent to the system PLC. The IO-Link connector also provides 24V to power the sensor.
Figure 3. Example smart proximity sensor with IO-Link.
A traditional power solution for the sensor circuitry would involve a low drop-out linear regulator (LDO). Let’s look at the power dissipation of the sensor circuitry, power supply, and total device. Old-school analog sensor circuitry typically consumes about 15mA. The 24V industrial power rail can reach 30VDC maximum. The power dissipations are as follows:
IO=15mA, Vi=30V (maximum)
In this example, only 75mW is used to do real work (powering the sensor circuitry), while 375mW is lost in the LDO due to its inefficiency. Our device must dissipate 450mW in total power. Adding more smart features to the sensor will require more current, which is not good news for the device’s power dissipation. Using our calculation above, if we were to increase the sensor circuitry current to 30mA, then: IO = 30mA, PSensor = 150mW, PSUP = 750mW, and PDevice = 900mW. 900mW exceeds the power dissipation limit of most small proximity sensors. So, heat is a big issue.
An alternative to the traditional LDO power supply solution involves using a miniaturized DC-DC power module. As Figure 4 shows, at 15mA sensor current and with a conservative 75% efficiency, the DC-DC power module has only 25mW of power loss. This helps to minimize the total device power loss from 450mW to 100mW, a 4.5x reduction in power dissipation.
Figure 4. Power supply dissipation – LDO versus DC/DC converter solution.
Thanks to the high efficiency of the DC-DC power module, the sensor can support more circuitry and features because of minimized heat and support for more sensor current. A couple of examples of power modules that fit well into miniature sensors come from Maxim’s Himalaya uSLIC family: the MAXM17532, a 100mA ultra-compact, wide-input-voltage uSLIC device, and the MAXM17552, which can operate up to 60V input voltage. These compact modules save space, reduce heat, and help simplify power supply designs.
As Industry 4.0 continues to drive demand for smart sensors, addressing the challenges around powering these sensors is easier now thanks to highly integrated DC-DC power modules. Learn more on this topic from my article in Electronic Design, “Empower Design Innovation Through Ultra-Small Power Supply Designs.”