How to choose ESD (TVS)for your circuit
How to choose ESD (TVS)for your circuit


How to choose ESD (TVS)for your circuit

(1) According to the IEC61000-4-2 international standard, TVS chips must be resistant to ESD impacts of at least 8 KV (MB, contact) and 15 kV (BM, air), and different manufacturers will also adopt higher impact resistance standard. When designing the application, you can make corresponding choices according to the application requirements of the customer’s portable products.

(2) The capacitance of TVS is an important parameter for choosing TVS for data interface circuit. For a circuit with a higher data/signal frequency, the chip capacitance will interfere more with the circuit, resulting in greater noise or attenuated signal strength; therefore, the capacitance range of the selected device needs to be determined according to the circuit requirements. For high-frequency circuits, the capacitance should be selected as small as possible (such as LCTVS, the capacitance should not exceed 3 pF), and for circuits that do not require high capacitance, the capacitance of the capacitor can be selected to be higher than 40pF.

(3) When selecting TVS chip applications, if the circuit may withstand the impact of peak pulse voltage (surge voltage) from two directions, bipolar TVS should be selected; otherwise, unipolar TVS can be selected.

(4) When TVS is applied, the working Vc value should be lower than the maximum voltage of the protected device. Vc is the voltage of TVS in cut-off state, and also the voltage passing through TVS when ESD strikes, it cannot be greater than the withstand limit voltage of the protected circuit.

(5) When TVS is applied, it cannot be in a breakdown state during normal working conditions, and it must be kept below VR. Considering the requirements of both VR and VC to select an appropriate TVS.

(6) In TVS application, the power should be determined by VCIpp according to the known surge current IPP, and the corresponding device should be selected; if the approximate range of IPP cannot be determined, it is better to choose a TVS with higher power.  

(7) When using TVS, attention should be paid to the PM parameter (the maximum peak pulse power dissipation value that can be tolerated). Under a given maximum clamping voltage, the greater the power dissipation PM, the greater its surge current withstand capability; at a given power dissipation PM, the lower the clamping voltage VC, the greater its surge current tolerance. The greater the ability. In addition, the peak pulse power consumption PM is also related to the pulse shape, duration and ambient temperature.

(8) When using TVS, it should be noted that the transient pulses that TVS can withstand are non-repetitive, and the pulse repetition frequency (the ratio of duration to intermittent time) specified by the device is 0.01%. If repetitive pulses appear in the circuit, attention should be paid to the accumulation of pulse power, which may damage the TVS chip.  

(9) In TVS applications, for the protection of small current loads, it is necessary to add a current limiting resistor in the circuit. As long as the resistance value of the current limiting resistor is appropriate, it will generally not affect the normal operation of the line, and it can also reduce the interference generated.Therefore, in the application, a TVS with a smaller peak power can be selected to protect the low-current load line.