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I want to use a 824021 TVS diode in my circuit. The input is 5V and the clamping for tehe TVS diode is at 7V.

Which of the following two connection diagrams is correct A or B? Or a better way to put it is, do I have to connect both terminals or can I just use the one terminal as shown in A?

A:

enter image description here

B:

enter image description here

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  • \$\begingroup\$ diagram B shows two diodes connected \$\endgroup\$
    – jsotola
    Oct 29, 2021 at 21:21
  • \$\begingroup\$ So the image in the middle is the TVS diode 824021. Do I need to connect the other terminal (second diode terminal) or can I leave it open? \$\endgroup\$
    – JoeyB
    Oct 29, 2021 at 21:22
  • \$\begingroup\$ you can leave it open \$\endgroup\$
    – Maple
    Oct 29, 2021 at 21:28
  • \$\begingroup\$ Both is correct. \$\endgroup\$
    – user263983
    Oct 30, 2021 at 0:19

2 Answers 2

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It depends on what you are protecting. While it is your choice, in your circuit you must consider the signals you are protecting.

If you put two diodes in parallel then you double the capacitance. This might impact the signals you are protecting. In this case the diode capacitance is about 60-70 pF, which is not insignificant. Doubling that to 120-140 pF could be quite a problem. For example, consider you might be protecting an HDMI high speed signal.

The most important element is that you look carefully at the impedance of the wires/tracks from your outer edge (connectors) to the protected circuits. Make sure you have ground pours on the PCB and impedance controlled signal tracks. When the TVS avalanches you need some early impedance/résistance against which to drop the excess voltage.

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You don't have to do anything, I mean: it is your choice.

Connecting only one diode and leaving the other pin open (your first schematic) is perfectly fine. You would then simply not use the diode connected to the unconnected pin.

But since you have two diodes anyway, I would use both in parallel as is shown in your 2nd schematic. You would get a slightly better protection because two diodes in parallel can handle more current than only one diode.

So: you can choose, both schematics are OK. I would prefer the 2nd schematic.

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