2
\$\begingroup\$

I have been wanting to update a design I have to include a USB to UART Bridge and while looking at the datasheet for the CP2102N saw what is in the image below. I have never worked with a TVS before so I am not entirely familiar with their specifications.

When the datasheet says to use "SP0503BAHT or equivalent USB ESD protection diodes (Recommended)" what exactly determines a TVS is 'equivalent' or 'better'?

While searching around I came across this post which has the TI TPD4S012 listed as a suitable USB TVS. I'm not looking for someone to verify that the TPD4S012 is a suitable replacement for the SP0503BAHT, rather, the understanding of what to consider when choosing.

CP2102N Datasheet

\$\endgroup\$
  • \$\begingroup\$ Why are TVS diodes shown in your picture - start from that point - understand why someone has decided it's a good idea for them to be there. \$\endgroup\$ – Andy aka Mar 20 '18 at 18:11
  • \$\begingroup\$ Certain RF rated TVS diodes have very low capacitance, as do some Gas Discharge Tubes (GDT). There are now tiny smd versions of TVS with only 1.5 pF of capacitance. \$\endgroup\$ – Sparky256 Mar 20 '18 at 23:08
2
\$\begingroup\$

Besides voltage and single or bidirectional the important parameters are the conductance or ESR and the capacitance .

the product of the two would be your figure of merit. The trade off Is that when ESR is reduced capacitance normally increases and capacitive loading the limit signal slew rate.

Because of the many variations , major distributors have search filters by application. From there choose the best bang for the buck.

Although many TVS diodes are rated for the induced lightning test 10/120 µs , this may be irrelevant for ESD protection where rise times on open cable contact can be sub-nanosecond

\$\endgroup\$
  • \$\begingroup\$ Since the SP0503BAHT has the spec of Rdyn: 1.0Ω to 1.4Ω; Cap: 30pF and is unidirectional, whereas the TPD4S012 is Rdyn: 1Ω to 1.2Ω; Cap: 0.8pF (on data lines) and is bidirectional as described in the answer provided by @crj11, then I am safe to say the TPD4S012 can replace the SP0503BAHT in this example. \$\endgroup\$ – SolveEtCoagula07 Mar 20 '18 at 19:13
  • \$\begingroup\$ They are similar maybe better in some tests, but not identical. Why not use the SP0503BAHTG which replaces SP0503BAHT? OK for speed USB2 \$\endgroup\$ – Sunnyskyguy EE75 Mar 20 '18 at 20:47
  • \$\begingroup\$ Also DRTR5V0U2SR \$\endgroup\$ – Sunnyskyguy EE75 Mar 20 '18 at 20:57
  • \$\begingroup\$ I thought it would be better to use something that is bidirectional and I was looking to find something a bit smaller than the SOT-143. \$\endgroup\$ – SolveEtCoagula07 Mar 20 '18 at 21:59
  • \$\begingroup\$ If space is a premium then the SON package is good \$\endgroup\$ – Sunnyskyguy EE75 Mar 20 '18 at 22:35
5
\$\begingroup\$

If you look at a parametric search for TVS diodes, you will see columns of the parameters that differentiate the diodes.

The most important are breakdown and clamping voltage, peak pulse power/current, and whether the device is bidirectional. Bidirectional diodes are back to back diodes so that they can clamp both positive and negative voltages. For high speed digital lines, the capacitance is also very important, since high capacitance will attenuate your digital signals.

If you choose a diode with similar breakdown/clamping voltages, peak pulse power/current, "bi-directionality", and capacitance, you should be OK.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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