Parameters and how to select TVS models for application

TVS Transient Voltage Suppressor. TVS diodes come in unidirectional and bid types, with unidirectional TVS typically used in DC power circuits and bidirectional TVS used in circuits with alternating voltage. Unidirectional TVS diodes are used in circuits, where they remain in an off state (high resistance) when the circuit is operating normally, without affecting normal operation. When a transient voltage spike occurs in the circuit and the TVS's breakdown voltage (avalanche), the TVS quickly changes from high resistance to low resistance, discharging the transient overcurrent caused by the abnormal overvoltage ground, and at the same time clamping the abnormal voltage at a lower level, thus protecting the subsequent circuit from damage caused by abnormal overvoltage. When the abnormal overvoltage disappears the TVS resistance returns to high resistance. The seven major parameters of TVS As shown in the above figure, TVS has the following seven major parameters: .VRWM Reverse Breakdown Voltage/Reverse Working Voltage The highest working voltage of the TVS, the highest working peak voltage or DC peak voltage that can continuously applied without causing deterioration or damage to the TVS. For AC voltage, it is expressed by the effective value of the highest working voltage. At VRWM, the TVS considered to be non-working, i.e. not conducting. The highest working voltage in circuit design must be less than VRWM, otherwise it will cause the TVS to and the circuit to malfunction. 2.IR Reverse Leakage Current The reverse leakage current is generally the standby current. The maximum current flowing through the TV under specified temperature and highest working voltage conditions. The leakage current of TVS is generally measured under the reverse working voltage, and for a certain model of TVS, IR should be the specified value range. For a voltage value VRWM applied to both ends of the TVS, the current read from the ammeter is the leakage current IR of the TVS For TVS of the same power and voltage, when VRWM is less than or equal to 10 V, the leakage current of bidirectional TVS is twice that ofidirectional TVS. Generally, the leakage current < 100 nA, for some analog ports, the leakage current will affect the sampling value of ADC, so smaller the leakage current of TVS, the better. 3.VBR Breakdown Voltage Breakdown voltage (breakdown voltage), the voltage at which ESD begins to work, is generally the voltage at which the TVS passes 1 mA, and the time of applied current generally does not exceed 400 ms to avoid the device. Min and max are deviations in the breakdown voltage of the TVS, and generally TVS has a deviation of ±5%. Measurements where VBR falls between and max are considered acceptable. 4.IPP Peak Pulse Current Peak current, the peak of a given pulse current waveform. TVS typically uses a current waveform of 0/1000 us or 8/20 us. 5.VC Clamping Voltage Clamping voltage, the peak voltage across the TVS when peak pulse current IPP is applied to the specified waveform. IPP and VC are parameters that measure the ability of the TVS to resist surge pulse current and limit voltage in circuit, and the two parameters are interrelated. For the same model of TVS, the larger the IPP, the stronger the ability to withstand current impact, and if VC is under the same IPP, it indicates that the clamping characteristics of the TVS are better. 6.Cj Junction Capacitance Junction capacitance is parasitic capacitance in TVS, which needs to be paid attention to in the protection of high-speed IO ports, and excessive junction capacitance may affect the quality of the. According to the protection signal rate, select the appropriate junction capacitance, and the following gives the recommended ESD junction capacitance size range for common interfaces.
7. TVS Power TVS power is the power at which the TVS will not be damaged by the surge current pulse when surge protection. TVS Selection (5a test pulse is taken as an example) 1. Determine the reverse stand-off voltage VRWM of the TVS di For example: if the product is a 24V system, the reverse stand-off voltage is generally required to be greater than or equal to the supply voltage, but the need for overvoltage performance testing, 36V is selected. 2. Determine the peak current of the TVS For example: the highest peak of the a pulse is 202V, and the output internal resistance of the test equipment is 4Ω (both of these are related to the test equipment and test standards) Then it can be known that the peak current Ipp of the TVS should not be less than 50.5A. 3. Determine the clamping voltage of TVS The clamping voltage Vcmax is generally 1.5~2 times of the reverse stand-off voltage VRWM, so the clamping voltage Vc range is selected as 54V~72V. 4. Determine the peak power of the TVS diode According to the clamping voltage and peak current it can be known that the peak power Pppm range of the TVS diode is 2.7kW~3.6kW. It should be noted that the a pulse is different from the surge pulse, its pulse width is large and the duration is long. When the pulse width is 5~10ms, the peak value reaches maximum of 202V, at this time, it is required that the power of the TVS diode should be above 3.6kW; while at 00ms, the voltage pulse peak is 84V, at this time, it should be required that the TVS power should be above 1.5kW. selecting the model, it is necessary to pay attention to the power-time curve of the device. 5. Confirm the selection: According to the above parameters, the TVS diode is used to protect the 5a pulse. The TVS diode is a unidirectional conducting TVS diode. The reverse stand-off voltage this TVS is 36V, and the maximum current is 114A, which meets the requirements. Look at the power-time curve above, power of the device protection at 10ms is 5.3kW, which is higher than the protection requirement of the peak power of 3.6kW; the power at 100ms is 1.8kW. Higher than the protection requirement of 1.5kW, so the selection is completed

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