Which is better bidirectional or unidirectional TVS diodes?
Bidirectional TVS diodes can absorb instantaneous large pulse power in both positive and negative directions, and clamp the voltage to a predetermined level. Bidirectional TVS is suitable for AC circuits, and unidirectional TVS is generally used for DC circuits.
Is the capacitance of a TVS diode proportional to its size?
Since the TVS diode’s capacitance is proportional to the physical size of the diode a practical solution is to decrease the overall size of the TVS diode which can effectively mitigate the performance degradation in the circuit due to parasitic capacitance.
How is the TVS diode connected to the circuit?
The TVS diode is connected in parallel with the protected circuit on the circuit board. When the instantaneous voltage exceeds the normal working voltage of the circuit, the TVS diode will produce an avalanche, providing an ultra-low resistance path for the instantaneous current. As a result, the instantaneous current is drawn through the diode.
What should be the PPR of a TVS diode?
TVS diodes should be selected correctly when using. The rated transient pulse power PPR should be greater than the maximum transient surge power that may occur in the protected device or line. TVS devices can be divided into unipolar and bipolar according to polarity.
The problem arose in the choice between unidirectional and bidirectional diodes. Doubts arose because I learned that the ESD voltage can be of different polarity, in some case a bipolar TVS could miss a pulse of reverse polarity and cause damage to the device. Tell me, is that so?
When does the ESD diode kick in for a positive spike?
For the positive spikes, the ESD diode will kick in into action soon after the voltage reaches the clamping voltage. For negative spike, the TVS diode acts as normal diode shorting the signal soon after the forward voltage of the diode is crossed.
What kind of TVS diode is used for negative spike?
For negative spike, the TVS diode acts as normal diode shorting the signal soon after the forward voltage of the diode is crossed. SMF series from little fuse has reverse stand off voltage starting from 5 V. General purpose ESD protection diode example is below: SP3222 0.9pF 30kV dual channel TVS for example can be used.
How to limit the value of an ESD strike?
Adding a small capacitor between the line and the ground also helps. Also consider adding a series resistor of a few 100 ohms depending on the baud rate of the UART. This will also helps in limiting the current value during an ESD strike.