IoT devices are commonplace in our everyday lives. From military applications to civilian household use, these nonstandard computing devices connect wirelessly to a network and have the ability to transmit data. However, IoT applications are plagued by unique electrical concerns that could compromise the lifespan and reliability of the connected devices. One such concern is how IoT devices could withstand constant ESD exposure without failing.
The obvious solution is of course, to use TVS Diodes as a mitigative measure. However, choosing a TVS diode for IoT devices isn’t as simple as it seems. You can’t approach ESD protection for IoT devices the same way as for typical applications like commercial alarm controllers or data loggers.
IoT devices bear unique characteristics that require certain types of TVS Diodes. In this article, we’ll explore the complexity of IoT devices, increased susceptibility to ESD, and how to choose the right TVS Diodes for protection.
Why IoT Devices Are More Susceptible To ESD
At a glance, it may seem that IoT devices are no different from other industrial or commercial electronic products. However, IoT devices tend to operate in challenging environments with high electrical and mechanical stress.
For example, military drones are used to survey battlefields, mapping out landscapes and adversarial positions in extreme temperatures and climate.
Temperature sensors and real-time equipment management applications on military fleets must withstand extreme cold and sudden bumps on tough terrain. These information sensors then transmit the data back to command centers.
There are health sensors attached to soldiers’ uniforms to offer proactive health surveillance back to command centers.
Medical implants must operate reliably for and beyond their rated lifespan in non-serviceable conditions.
Reliability and durability are key to developing IoT devices, but hardware designers face a threat that comes from none other than the users themselves. ESD, or electrostatic discharge, is a phenomenon whereby static electric charges are transferred from humans to IoT devices.
Certain types of IoT devices experience more direct contact with humans than others. For example, military and medical implant devices, smart command center touch panels, and even down to our smartwatches and home smart doorbell.
The frequent human exposure means the underlying IoT components will suffer more instances of ESD impulses. Highly charged ions may couple through the capacitive sensing button, touchscreen, and PCB tracks near the point of exposure. This will inevitably shorten the lifespan of the components or cause outright damage to the IoT device.
(Image from Military Wearable Sensors Market)
Why Conventional ESD Protection Is Not Enough
If you’re hoping to rely solely on component-level ESD protection, you’re taking a huge risk. While components like microcontrollers and wireless ICs are rated for ESD protection, they may not be enough for the robust requirement of IoT devices.
For example, the IEC 61000-4-2 standard specifies ESD protection of up to 15,000 V air discharge, but the actual charge released by humans can go up to 30,000 V or more. Not all components for IoT development are designed to withstand high discharge voltage. The MSP430FR25 series capacitive sensing microcontroller is only rated for 1,000 V based on the Human Body Model.
Regardless of your choice of components, you will require system-level ESD protection to ensure that the device withstands repetitive exposure to high static discharges. Component-level protection is likely to prevent the device from ESD failure during assembly and testing in a controlled environment but not real life usage.
Many of these IoT devices have to be prepared for a variety of conditions. For example, a person going for a slow jog with a smartwatch in the park may not pose many problems. But if he/she is wearing the smartwatch in a low-humidity carpeted room, the risk of exposure to high ESD voltage is significant. So, when it comes to soldiers wearing IoT devices in combat scenarios, they need to be protected from extreme circumstances.
How TVS Diodes Protect IoT Devices From ESD
It’s evident that banking on on-chip ESD protection is not wise as the total solution. As such, you’ll need additional protection on the system level. That’s where TVS diodes come in. A TVS diode is a semiconductor component for suppressing transient voltage and protecting components from sudden spikes.
In IoT devices, TVS Diodes play an important role to keep components from direct exposure to static discharges. It is placed in reverse bias configuration on the signal path prior to the component that requires protection.
The TVS Diode appears as an open circuit between the signal path and ground on normal conditions. As long as the voltage on the electrical path is below the reverse standoff voltage, no current will pass through the TVS Diode.
The TVS Diode starts conducting when the voltage on the electrical path exceeds the reverse standoff voltage. It will conduct a huge amount of current when its breakdown voltage is exceeded. At this point, the TVS Diode will shunt excessive current to the ground and clamp down, limiting the voltage level on the signal path.
To get optimum ESD protection, you’ll need to place the TVS Diodes before the components. Ideally, you’ll want to place TVS Diodes close to human interaction points. This ensures that static charges are safely shunted before reaching the components.
How To Choose TVS Diodes for IoT Devices
When it comes to choosing TVS Diodes for electronic development, you’ll need to ensure these parameters are within the required range.
- Reverse Standoff Voltage (VRM) – The maximum point where the TVS diode does not conduct.
- Reverse Breakdown Voltage (VBR) – The threshold where the TVS diode starts to conduct current.
- Clamping Voltage (VCL ) – The voltage level when the TVS is conducting current.
- Peak Pulse Current ( IPP) – The maximum current that the TVS diode can withstand without failing.
These parameters determine if the TVS Diode fits the operating voltage of the components, and the threshold for it to start conducting. Also, choosing the right parameters ensures that the TVS Diode clamps down to a voltage within the allowable limit and capable of shunting an expected amount of current.
(You can find a detailed description of the parameters in our article here.)
Besides the above parameters, you’ll need to pay attention to the following ones due to the unique nature of IoT devices.
With IoT devices like smart wearables getting smaller in size, the design area is becoming a luxury. Most TVS Diodes are available in the SOD882 package, but you will need form factors like the 0201, 01005, or smaller for IoT applications. Our SMCJ-series is a great option with a 0.28 m x 0.245 mm package dimension.
TVS Diodes vary in capacitance. A high capacitance value will cause integrity issues on high-speed signals. To protect high-speed interface on IoT devices, you’ll need one with low capacitance, or to configure it to limit the capacitance, preferably in single pF or lower.
Many IoT devices are battery-powered. In such designs, every microAmp of current consumed by the load matters. Therefore, you’ll need to choose a TVS diode with an ultralow leakage current when it’s not conducting. This ensures that the IoT device has an optimal battery lifespan.
TVS Diodes are pivotal in ESD mitigation for IoT devices. These tiny components safely keep electronic components from high static charges unleashed from human interaction. We’ve shown you why relying on component-level is not enough and why you’ll need to choose IoT-optimized TVS diodes.