By Brian Condell and Michael Jackson
If you’re in the business of designing industrial sensors for smart factory applications, then power density is one of your daily challenges. On the one hand sensor enclosures are shrinking but on the other, everyone wants them to have more features. Even if you can make the electronics physically fit inside the sensor casing, there is another unseen factor that can cause your device to fail – power dissipation in the form of heat. Many industrial sensors use either an M8, or a larger M12 cable connector (Figure 1) and this impacts the size of the sensor enclosure and hence the amount of heat that it can dissipate. IO-link provides your sensor with the intelligence it needs but to get around the problem of heat, you need to know what to look for when deciding on what transceiver to use. In this blog, we provide you with some useful design tips to help you make the right choice.
Figure 1 - Industrial sensor with M12 connector
Suppose you want to design an IO-Link sensor with a total power dissipation that does not exceed 400mW if it’s using an M8 connector or 600mW for an M12 (for example).
Apart from a transducer (pressure/temperature/proximity), your sensor will also typically include the following:
- Analog front-end (AFE),
- Status LEDs
- Cable driver output stage
Industrial sensors use a 24VDC (typical) voltage, but in a harsh factory environment, this often climbs to levels up to 25% higher. While these voltage levels can be safely used to power the output driver stage, the AFE, LEDs, and microcontroller require much lower voltages (typically 2.5V to 5V) for operation. Many IO-Link transceivers provide a linear regulated output (LDO) voltage but using this to power these circuits can have a major impact on power consumption. For example, consider the following power budget for a small sensor drawing only 15mA of current from the L+ DC rail. Because of the inherent inefficiency in how an LDO works, this relatively low-power sensor exceeds the ~400mW power-budget for an M8-connected enclosure, meaning you would have no option other than to use the larger M12. A 30mA sensor would be even worse – dissipating 1000mW in total and exceeding the target figure for an M12 connected enclosure.
Figure 2 - Power Budget for LDO-powered sensors
One way to reduce power dissipation is to use a DC-DC buck converter instead of an LDO. For example, using a 3V DC-DC buck converter to power your 30mA sensor would use only 90mW of power. Assuming the converter is 90% efficient (meaning 9mW of power loss), the total power dissipated in the sensor would be approximately 200mW (Figure 3). Clearly, using a DC-DC converter helps to reduce power dissipation by nearly 80%, but this comes at the expense of using extra external circuitry (bulky discrete components such as an inductor, diodes, and capacitors), which may not even fit in the sensor enclosure.
Figure 3 - Comparing power dissipation using a DC-DC converter vs. LDO
The best overall solution is an IO-Link transceiver with an integrated DC-DC converter, like the MAX22513 (Figure 4). This IC can supply up to 300mA (comfortably exceeding the 200mA minimum specified for IO-Link) from a programmable output voltage (2.5V to 12V). It also includes an auxiliary IO Link channel which can be used for DI/DO sensor switching while data is being transferred on the C/Q channel. Additionally, this transceiver comes with integrated surge protection (up to ±1kV/500Ω) circuitry, which means you get robust performance without the need for external TVS diodes.
Figure 4 - MAX22513 IO-Link Transceiver with Integrated DC-DC
Even with all these extra features, the overall area of this WLP device is only 2.1 × 4.1mm. For even more space-constrained sensors, the MAX22514 is a variant of the MAX22513 which comes in an even smaller WLP measuring only 2.5 x 2.6 mm. Conveniently, both transceivers can also be used in the design of IO-Link Devices and IO-Link Masters.
The MAX22513 and MAX22514 really are the answer to the space vs. power conundrum for your smart factory sensors!