0
\$\begingroup\$

Once can find integrated TVS diodes without and with the VDD connected for high speed bus protections:

For example NXP IP4282CZ6 (no VDD):

enter image description here

For example Wurth 824015 (With VDD):

enter image description here

What is the practical difference in using/ operation between the 2? Both use Zener diode for the VDD to GND connection (low break voltage = high capacity which does not matter for VDD to GND connection). But the former has no VDD connected to the diodes anodes. Is the voltage peak supposed to go through the given Zener diode? In that case the capacity becomes an issue after all?

\$\endgroup\$
1
  • \$\begingroup\$ You'll have to ask the manufacturers, why they make devices that are essentially identical but with the VDD pinned out or not (e.g. SOT23-5 vs. SOT23-6, identical outline, no advantage in layout area). \$\endgroup\$ Jul 25, 2022 at 21:06

2 Answers 2

1
\$\begingroup\$

It depends on the topology of the sockets you want to protect.

For example, for USB where you have D+/D- and VBUS to protect, it is a good idea to have a VDD input on the protection device to cover all the pins of the USB connector (assuming there is no ID pin).

No worries, it won’t affect the line capacitance of I/Os inputs.

So, at the end they are options provided by the semiconductor vendors.

The text below from ST USBLC6-2SC6 datasheet may help you to better understand the current path and the 2 behaviors of the protection device in case of positive or negative surges: rail to rail ESD protection surge clamping voltage calculation rail to rail ESD protection current path, parasitic inductances and layout recommendations https://www.st.com/resource/en/datasheet/usblc6-2.pdf

\$\endgroup\$
2
  • \$\begingroup\$ Thank you for the answer. I understand the explanations from the DS, but there are a lot of integrated TVS dedicated for USB 2.0 without the path to the VDD (GND only). What could be the case here? \$\endgroup\$ Aug 1, 2022 at 7:27
  • 1
    \$\begingroup\$ You're welcome. Some people want to have a super robust protection on the VBUS and they prefer to use a much powerful TVS like SMA6J5.0A-TR. Sometimes as well, the VBUS voltage can be up to 9V, 15V and up to 20V with USB power delivery. So they cannot use the VDD pin of the protection which is a 5V protection cf ECMF02-4CMX8 \$\endgroup\$
    – Jean
    Aug 1, 2022 at 9:01
0
\$\begingroup\$

Some analog IC's have a maximum differential voltage much smaller than the supply, yet the common mode range is much larger. (Some FET input OA's)

CMOS logic has a critical differential relative to Vdd,Vss to prevent latchup.

These are just 2 applications with different requirements.

\$\endgroup\$
2
  • \$\begingroup\$ Thank you for the answer. I normally see no VDD options used for busses like USB, yet the VDD option is sometimes used as well...? \$\endgroup\$ Jul 25, 2022 at 21:04
  • \$\begingroup\$ 1. Product profile 1.1 General description The IP4282CZ6 is designed to protect high-speed interfaces such as HDMI, DVI and DisplayPort interfaces. The device includes high-level ElectroStatic Discharge (ESD) protection diodes for the TMDS signal lines. \$\endgroup\$ Jul 25, 2022 at 21:21

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.