This article examines the impact of ESD in automobiles and outlines some of the best circuit protection devices and techniques for minimising ESD.
Electrostatic discharge or ESD occurs when there is a sudden discharge of electricity between two bodies, typically due to contact, dielectric breakdown (e.g. moist air separating the objects), or short circuits.
ESD can also build up due to the constant rubbing of two dissimilar materials (aka triboelectric charging). When an ESD strike occurs, the electric field or spark generated can damage sensitive components. However, with a suitable ESD protection device, the excess voltage can be diverted from the PCB within a fraction of a second.
A warning label for an electrostatic-sensitive device.
ESD Protection Techniques in Automobiles
Automotive infotainment, security, and driver-assistance features leverage advances in component miniaturisation, which allows for higher computing power within smaller geometries. However, as under-the-hood electronics are sensitive to ESD, automakers must use ESD protection to ensure the optimum safety and reliability of components.
According to the IEC 61000-4-2 standard, automakers must ensure at least Level 4 ESD immunity, which translates to ±8kV contact discharge, and ±15kV when in the air. However, some carmakers go above and beyond these requirements (up to ±15kV contact discharge, and ±25kV when in the air). Efficient ESD protection can improve the safety and reliability of automotive electronics.
We will now discuss how electrical engineers can utilise ESD protection devices in specific areas of automobiles, such as media interfaces (USB and HDMI connectors) and lighting modules.
ESD Protection in Media Interfaces
USB 3.0/3.1/Type-C ports in modern cars and trucks enable high-speed data transfer (up to 5Gb/s in USB 3.0 and 10Gb/s in USB 3.1) and charging for portable devices, such as smartphones, wearables, and tablets. However, these connections may be susceptible to ESD damage (e.g. through frequent plugging and unplugging, or contact with charged bodies).
ESD in USB ports can cause latent or catastrophic failures in PCB components, such as ICs, MOSFETs, and RF antennas. High-definition multimedia interface, or HDMI, ports utilised in rear-seat infotainment systems are also prone to damage during overvoltage events.
Both HDMI and USB 3.0 connectors have pin configurations that include differential pairs for the transmitting high-speed signals. For adequate ESD protection in these ports, engineers can integrate silicon ESD (SESD) devices.
SESD devices are uni-directional or bi-directional—components capable of providing ESD protection up to tens of kilovolts (kV) for both contact and air discharge. Additionally, they have ultra-low capacitances and low insertion losses (suitable for high-speed signals).
A USB device connected to a car's infotainment system.
ESD Protection in Automotive Lighting
Light-emitting diodes, or LEDs, utilised in automobiles’ interior and exterior lighting schemes are affected by ESD events, which causes premature failures and potential safety issues. Automotive LED modules comprise built-in ESD protection devices to protect these components. Otherwise, engineers can connect polymer ESD (PESD) protection devices in parallel with LED input terminals to prevent ESD intrusion.
A useful component for minimising ESD in automotive electronics is the transient voltage suppression (TVS) diode. TVS diodes protect sensitive circuits from damaging voltage spikes by shunting the excess current in the system, and then they ‘reset’ themselves after the voltage level returns to normal.
TVS diodes are uni-directional or bi-directional components that clamp down voltage levels that rise above a breakdown threshold. During ESD events, they can respond within nanoseconds, providing reliable protection.
Testing for ESD Immunity in Automotive Systems
One of the best-recognised standards for testing the ESD immunity of automotive components is the ISO 10605 standard. ISO 10605 provides procedures for simulating ESD due to human contact inside or outside of a vehicle using test voltages of 15kV to 25kV for air gap discharge and 2 kVto 15kV for contact discharge.
The device under test (or DUT), such as an automotive-qualified part placed on a test bench, receives thousands of kilovolts from an ESD simulator via a discharge gun. Automakers will interpret the test data to determine the amount of damage and choose the most suitable ESD protection device.
We can do a lot more with automobiles these days, owing to innovative driver-centric features, such as infotainment systems, GPS and location mapping, hands-free communications, and many more. For example, drivers can place calls, consult maps, and more—all at the push of a button (or even through voice commands in many cases).
Given the growing trend of cars with built-in infotainment, security, and driver assistance features, the number of electronics under the hood are on the rise. Thus, there is now a greater need to safeguard them from electrostatic discharge impacting the overall safety and reliability of the vehicle. Integrating ESD protection using TVS diodes and silicon and polymer devices are just some of the ways that electrical engineers can help safeguard the future of mobility.