ESD Protection TVS - Page 1
Forum section: electronics / beginners

author: Darlington
author_rank: Contributor
timestamp: July 21, 2025, 10:42:42 am
content: Hi guys,I would like to effectively protect the GPIO pins of an ESP2-S3-WROM1.I often see TVS diodes such as:PESD3V3L1BA (Nexperia)ESD5Z3.3T1G (OnSemi)But I don't understand how they can effectively protect the pins, as the clamping voltage is much higher than the maximum voltage applicable to the pin reported in the module's SOA.Why is this done?

author: xvr
author_rank: Frequent Contributor
timestamp: July 21, 2025, 12:38:54 pm
content: Single TVS is not enough for protection. Something like this circuit neededHere TVS D4 absorbs the ESD pulse, D5 and D6 limit the remaining ESD voltage to the power rails. Resistor R23 limits the current flowing through D5 and D6.D5 and D6 may be a part of the input circuit of a connected microcontroller.

author: PGPG
author_rank: Frequent Contributor
timestamp: July 21, 2025, 02:15:46 pm
content: Quote from: xvr on July 21, 2025, 12:38:54 pmIn this case it absorbs also a signal

author: fourfathom
author_rank: Super Contributor
timestamp: July 21, 2025, 02:38:49 pm
content: Quote from: PGPG on July 21, 2025, 02:15:46 pmAnd that is because (in the schematic) the TVS is backwards. When oriented the proper way there will be very little signal degradation due to the extremely low capacitance of the non-conducting TVS (< 2pF, often less than 0.5 pF.)

author: xvr
author_rank: Frequent Contributor
timestamp: July 21, 2025, 03:04:12 pm
content: QuoteYes, you right. My falut - TVS should be reversed.

author: Darlington
author_rank: Contributor
timestamp: July 21, 2025, 07:18:05 pm
content: Okay, now it's clear.The TVS diode alone is not enough; diodes must be placed on the power rail, but by doing so, isn't there a risk of breaking the MPU itself due to the increase in rail voltage?Which of the above diodes is the best choice, or are there any better ones?

author: xvr
author_rank: Frequent Contributor
timestamp: July 21, 2025, 09:48:15 pm
content: QuoteIt could. To avoid such break you should select R value to limit maximum current injected in power rail to value less than current, consumed by whole circuit.

author: MariuszD
author_rank: Regular Contributor
timestamp: July 22, 2025, 05:05:37 am
content: Diodes D5 and D6 are always inside the integrated circuit. For small currents, they serve as protection, for larger currents, they cause damage not only to a single pin but to the entire integrated circuit. ICs with good documentation provide the "maximum injected current" data, which is only a few mA, but the ESP32 documentation lacks this information. You need to protect the internal diodes with external diodes. But you don't know how much these diodes can withstand. Sometimes it is only 1mA, I think we can assume that the ESP32 can withstand injected current of 1mA. If you are using analog peripherals (e.g., ADC), causing the internal protection diodes to conduct will disrupt the operation of these peripherals.

author: Darlington
author_rank: Contributor
timestamp: July 22, 2025, 04:17:18 pm
content: @MariuszDI try to simulate everything with LTspice, trying to keep the injection current low, well below 1mA.My reasoning is as follows:The V2 generator is a function that varies from zero to the VC voltage of the TVS (ESD5Z3.3T1G).Resistor R2 determines the current of diode D1 when V2 approaches the output voltage of the LDO at 3.3V. Would it be a good idea to replace it with a PTC fuse?Resistor R1 determines the current of diode D3 inside the ESP32.R3 is the high input impedance of the GPIO pin, could the value be similar to reality for low-frequency signals?I set the same model for the four diodes.Could this work? How can I simulate an increase in rail voltage caused by high input voltage?Attached are screenshots of LTspice and *.asc files.

author: fourfathom
author_rank: Super Contributor
timestamp: July 22, 2025, 04:44:00 pm
content: I wouldn't use a PTC since they have a significant thermal delay before the onset of current limiting.

author: PGPG
author_rank: Frequent Contributor
timestamp: July 23, 2025, 10:43:35 am
content: Quote from: Darlington on July 22, 2025, 04:17:18 pmI don't use simulation at all (in past (90s-2005) I was using it practically to simulate only supply filters made from elements with their parasitics).Making a enough close to reality simulation is simply too time consuming in my opinion.In your case:Do you think that Rser=0.5 is good approximation of your supply not when it is loaded (like in normal work) but when it is supplied from its output side (not intended situation).

author: Darlington
author_rank: Contributor
timestamp: July 23, 2025, 04:18:24 pm
content: This is difficult for me to determine.Iis it possible to use a shunt such as the ATL43x as a Zener diode after the TVS diode so that the overvoltage is not connected to the rails but to ground?Quote from: PGPG on July 23, 2025, 10:43:35 am

author: PGPG
author_rank: Frequent Contributor
timestamp: July 23, 2025, 05:14:34 pm
content: Quote from: Darlington on July 23, 2025, 04:18:24 pmAt your last schematic you didn't had TVS diode but at input you had diodes to your supply (GND and VCC). It is why I drew your attention to what will happen if ESD current you direct into your supply.If there is TVS diode than problem is smaller as current into second protecting stage can be reduced by R.Problem with ESD is that it is very fast pulse. When humanity had oscilloscopes that could show a 5ns edge, the conclusion was that ESD builds up in 5ns. Now it looks that it rises in 1ns. But as we get tools allowing to see shorter slopes we then see that it is always our tool that determines the slope time we see and not ESD pulse itself.This means very high dI/dt and this means that inductance of even few mm wire is enough to get several voltages at it.I remember long time ago reading in one of D.Smith Tidbits that he got 200V at small voltage transil during ESD flowing through it.https://emcesd.com/Elements with feedback (like ATL43x) are too slow to have a chance to be able to react. But after the resistor which also has its inductance (what slows down the slope) this is a different story.