A Comparison of Varistors and Diodes

1. A Comparison of Varistors and Diodes

2. Varistors and Diodes Special Note:These comparisons hold whether comparing discrete chips (TransGuard vs. diode) or arrays (MultiGuard vs. diode)

3. Summary of Advantages • Varistors have many advantages over diodes. These include: • Reliability • High temperature performance • Board space consumption • Bipolarity • Turn On Time • Filtering characteristics

4. Reliability • Varistors survive many more ESD strikes than do diodes. 80000+ Pulses to Failure Energy

5. Reliability • A very small 0402 varistor provides more strike protection than a large SOT-23 diode

6. Current The ceramic material is doped Zinc Oxide where every grain is a Schottky Diode. The structure between the plates gives series/parallel diodes. The entire volume dissipates energy. Reliability

7. Varistor Better temperature performance Diode High Temperature Performance • Varistors maintain their energy handling capabilities at higher temperatures than diodes

8. 0402 TransGuard SOT 23 Diode 0.112” 0.067” 0.120” 0.020” Total Area = Total Area = 0.00134 in2 0.01340 in2 Board Space Consumption • Discrete varistors are much smaller than discrete diodes: Reduction of 90% in board space required!

9. Board Space Consumption • Varistor arrays consumer much less boards space than diode arrays 0508 MultiGuard SOT363 Diode Array Reduction of 37% in board space required! 0.098” 0.067” 0.080” 0.087” Total Area = 0.00536 in2 Total Area = 0.00853 in2

10. Board Space Consumption • Varistor arrays consumer much less boards space than diode arrays SO-8 Bi-directional Diode Array 0508 MultiGuard Reduction of >90% in board space required! 0.298” 0.067” 0.080” .197” Total Area = 0.00536 in2 Total Area = 0.0587 in2

11. Bipolarity • Diodes protect in only one polarity • Many of the diode array packages protect only in one polarity • In order to protect in both polarities like the varistors, the number of elements is cut in half! • A 4-element unipolar diode array is only a 2-element bipolar diode array!

12. Turn On Time • The performance of an ESD protection device is measured by the amount of energy that the device allows to be passed to the circuit (or device) being protected. • The key measure of a device’s ability to reduce the amount of energy passed is measured by the turn of time of the device. • The turn on time of varistors is much less than the tune on time of a diode

13. Turn On Time Sub-nanosecond turn on time

14. Turn On Time TransGuard Turn-on Time ~ 400ps Silicon TVS Turn-on Time ~ 1200ps ESD Waveform Unprotected Energy passed to circuit by the Diode

15. Filtering Characteristics • Diodes have very low capacitance, so they do not have filtering characteristics. • In fact, to achieve filtering and bipolar protection, 3 components must be used for the diode solution as compared to a single component for the varistor solution.

16. Filtering Characteristics • Again, varistors provide EMC filtering as seen in these S21 curves • Varistors can be manufactured to filter at different frequencies while still providing transient protection

17. Summary of Advantages • Varistors have many advantages over diodes. These include: • Reliability • High temperature performance • Board space consumption • Bipolarity • Turn On Time • Filtering characteristics