TVS diode is a component commonly used to protect sensitive electronic circuits. It can absorb and suppress overvoltage events in the circuit in an ultra-short time, preventing transient events such as electrostatic discharge (ESD), lightning strikes, power supply fluctuations, etc. from damaging the system. Choosing a suitable TVS diode is crucial to ensuring the reliability of the circuit.
1. Working Voltage
The reverse working voltage (VRWM) of the TVS diode must be higher than the normal working voltage of the circuit to avoid leakage current during normal operation and affect system performance. It is usually recommended that the working voltage of the TVS diode be about 10% higher than the maximum working voltage of the circuit. For example, if the system voltage is 5V, it is more appropriate to choose a TVS diode with a VRWM of about 5.5V.
2. Breakdown Voltage (Breakdown Voltage, V_BR)
The breakdown voltage of a TVS diode refers to the threshold voltage at which it enters the on state. Generally, the breakdown voltage should be higher than the maximum working voltage of the circuit, but must be lower than the maximum absolute rated voltage of the circuit to ensure that the protection system can be quickly turned on when a transient event occurs. Therefore, when selecting a TVS diode, it is necessary to confirm that its breakdown voltage range can match the voltage window of the target application.
3. Clamping Voltage (V_C)
The clamping voltage of a TVS diode during a transient event is an important parameter, which indicates the maximum voltage value at which the diode limits overvoltage. V_C must be lower than the withstand voltage limit of the protected device to ensure that the device is not damaged. When selecting a TVS diode, you can obtain the V_C of the TVS diode by consulting the data sheet. In practical applications, it is recommended to select a TVS diode with a V_C slightly lower than the maximum withstand voltage of the device.
4. Peak Pulse Current (I_PP)
The peak pulse current (IPP) of a TVS diode determines the maximum current it can withstand during a transient event. When selecting a TVS diode, it is necessary to evaluate the maximum transient current that the system may encounter and select a model that can provide sufficient IPP. Usually, the specification of a TVS diode will give the I_PP value under different waveforms (such as 8/20μs). Make sure the device you choose can handle the worst current surges.
5. Response Time
The response time of TVS diodes is extremely short, usually in the picosecond (ps) level. For sensitive devices, response time is an important parameter because it determines whether the TVS can suppress transient voltages in time. Although most TVS diodes can be turned on in a very short time, for some high-speed data transmission circuits, it is still necessary to pay attention to whether their response speed is fast enough.
6. Package form and heat dissipation capacity
The package form of TVS diodes not only affects its installation method, but also its heat dissipation capacity. For high-power applications, such as power protection and industrial equipment, SMC or DO-214 packages with better heat dissipation performance need to be selected; for portable devices with limited space, small packages (such as SOD-323) can be selected. At the same time, it is necessary to ensure that there is a good heat dissipation path at the TVS installation location to avoid high temperature causing device failure.
7. Choice of bidirectional and unidirectional TVS
Depending on the application requirements, unidirectional or bidirectional TVS diodes can be selected. For DC circuits, unidirectional TVS is usually selected; for AC circuits or scenarios with bipolar signals, bidirectional TVS diodes are required. On data lines, interfaces such as USB or HDMI often use bidirectional TVS diodes to protect against possible electrostatic discharge of positive and negative polarities.
8. Leakage Current
Under normal working conditions, TVS diodes should try to avoid excessive leakage current, especially for devices that are sensitive to power consumption, such as battery-powered portable devices. When selecting, it is necessary to check the leakage current specification of the TVS diode and ensure that it is within the system's allowable range.
9. Compliance with standards and certification requirements
For certain key areas, such as automotive electronics and medical devices, TVS diodes also need to comply with specific industry standards (such as AEC-Q101 certification). When selecting TVS devices for these areas, models with corresponding certifications should be given priority to ensure their reliability and compliance.
The selection of TVS diodes requires comprehensive consideration of multiple factors such as voltage, current, response time, packaging form, and certification requirements. Reasonable selection of TVS diodes can effectively improve the electronic system's ability to resist transients and reduce equipment damage caused by voltage surges or electrostatic discharge.
