Protecting Keyboards From Electrostatic Discharge (ESD) Events
17 May 2023 / by Anindita Bhattacharya
The Importance of Keyboard ESD Protection
Since the dawn of computers, the keyboard has been the primary communication mechanism between human and machines. Over the years, many technologies and interfaces have changed, but the keyboard has barely changed in both form and function. Recently, I bought an exclusive wireless keyboard. Initially, it communicated with the computer via Bluetooth without any issues. However, after a month or so, it suddenly stopped. When I opened the internal circuit, I was surprised that the keys had no electrostatic discharge (ESD) protection. Any electronic device's keypad, side keys or push buttons are vulnerable to ESD due to constant human interaction with them. Adding ESD protection devices in a keyboard/keypad/side keys can avoid disastrous situations such as the failure of my keyboard. Let us discuss ESD in general and how we can protect our electronic devices from it.
Electrostatic Discharge (ESD) and Its Impact on Keyboard ESD
ESD happens as a result of static electricity discharges. Static electricity is the combination of charged particles on the surface of any device or element. When an element with a higher charge comes in contact with another element with a lower charge, electrons flow from one element to another. An electric field can also induce the sudden flow of electrostatic charge. This transfer of charges may lead to a rapid flow of high current for a short time, and an ESD event occurs, reaching up to thousands of volts. Think of it this way; what if you were hit by lightning? That is a naturally occurring ESD event. Every time an ESD event happens, you have the potential to damage the internal circuitry of the keyboard controller, thereby causing it to fail; tiny lightning strikes happen to your equipment. The keyboard/keypad/side keys are contained in a non-conductive case, and touching the contacts directly with a finger is impossible. However, the flow of electrostatic charge can happen via air discharge, even in a non-conductive case. Hence, keyboard/keypad/side key ESD protection is not just important; it is essential to the long-term dependability of the controller circuit.
Recommendations on Protecting a Keyboard from ESD with Circuit Protection Devices
ESD protection can be achieved by placing a transient voltage suppression (TVS) diode on a data line to protect against transient events in less than a nanosecond. Under normal operating conditions, the TVS diode presents a high-impedance path to the protected circuit, making the TVS appear open. During a transient event, the TVS diode offers protection by providing a low-impedance way to divert the transient current from the circuit. You can learn more about what TVS diodes are here.
Figure 1. ESD protection of a keyboard
Examples of ESD Protection Circuits and Devices for Keyboards and Side Key Protection
Figure 1 shows the ESD protection of a keyboard matrix with TVS diodes. Keyboards are normally powered at an operating voltage of 5V via a USB interface or 2 to 4 AA batteries for wireless communication. Semtech's TVS diode, µClamp®5031ZA, features outstanding ESD protection characteristics. It has an operating voltage of 5V and is rated for a maximum peak pulse current of 7.5A (tp=8/20µs). The typical clamping voltage at a peak current of 4A is 7.5V. The dynamic resistance shown in Figure 2 is only 0.008Ω. µClamp5031ZA provides transient protection as per the specification in IEC 61000-4-2 (ESD) at ±30kV (Air) and ±30kV (Contact). The ESD clamping waveform of +8kV contact is shown in Figure 3. This bidirectional TVS diode is available in a tiny 0201 DFN package (0.6x 0.3 x 0.25 mm).
Figure 2. TLP characteristic of µClamp5031ZA
Figure 3. ESD Clamping (+8kV Contact) of µClamp5031ZA
Side Key Protection for Portable Devices
Another part we can mention here for protecting either a keyboard or side keys of a portable device is µClamp0541Z. The side keys may suffer from ESD strikes when they come in contact with a user. Most of the side keys of any portable device are DC switches working at an operating voltage of 5V or less. Semtech's µClamp0541Z features superior ESD protection characteristics and is perfectly suited to safeguard side keys and keypads from ESD events (Figure 4). It has an operating voltage of 5V and is rated for a maximum peak pulse current of 2A (tp=8/20µs). The typical clamping voltage at a peak current of 2A is 15V. µClamp0541Z is capable of withstanding high ESD with voltages ranging from ±17kV (Air) and ±17kV (Contact) as per IEC 61000-4-2 standard. The low dynamic resistance of 0.78Ω and a minimum reverse breakdown voltage of 6V ensure system-level protection against transient events. The TLP characteristic of the part is shown in Figure 5. The bi-directional µClamp0541Z comes in industry-standard ultra-small 0201 (0.6 x 0.3 x 0.25mm) packaging.
Figure 4. ESD protection of side keys
Figure 5. TLP characteristic of µClamp0541Z
Multi-Line ESD Protection for Keyboards and Keypads
So far, we have been discussing single-line protection from ESD. However, the number of keypad/side-key protection lines varies with the applications. Semtech offers options for the protection of multiple lines. At the same time, engineers can select unidirectional or bi-directional TVS diodes per the protection requirements. Ultra-low capacitance is not compulsory to protect the side keys and keyboards. Figure 6 shows the protection of four data lines of a keypad with Semtech's µClamp0504A. µClamp0504A has an operating voltage of 5V and is rated for a maximum peak pulse current of 7A (tp=8/20µs). The typical clamping voltage at a peak current of 7A is 12V. µClamp0504A is available in a SOT-666 package (1.7 x 1.7 x 0.6 mm).
Figure 6. ESD protection of four lines of a keypad
Ensuring Longevity and Reliability with ESD Protection
A keyboard, keypad, or side keys are still essential parts of our electronic devices in 2023. When you are designing a keyboard for a computer or any other device with keypads and push buttons, you should strongly consider adding protection devices like ESD protection circuits or ESD protection diodes to ensure that they are safe from ESD surges and to create a longer life and a higher perception of quality in your product. It may certainly add components to the BOM, but the users will appreciate a fault-free, glitch-free use of a keyboard for years rather than buying a new one in a short period of time. The last thing any user would want is to experience lost communication to their computer or failure of their new input device. Semtech is a prominent manufacturer of TVS diodes that protects many of the world's most modern electronic devices. Use Semtech's TVS diodes to foolproof your circuit. Learn more about Semtech's Circuit Protection products at the link below.
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