ESP32 Forum

Hello everyone,
I'm designing a PCB for a commercial product using an ESP32-S3, and I'm facing a challenge with its 3.3V power rail protection against ESD and other fast transients.

Here's the core issue:

• The ESP32-S3 has a very strict Absolute Maximum Rating for its VDD33 power supply of 3.6V.

• My PCB's main power rail is 3.3V, regulated by an LDO.

• I'm looking for an appropriate TVS diode for this 3.3V line (ideally at the main input, or near the ESP32-S3's power pin).

The problem I'm encountering with available TVS diodes is the "protection gap":

• Most suitable TVS diodes I'm finding (e.g., Nexperia SOT-23-3, 1- or 2-channel, some bidirectional options exist) have a Working Voltage (Vwm) of 3.3V.

• However, their Breakdown Voltage (Vbr) is typically around 4.2V to 4.5V.

• This means there's a "window of vulnerability" for the ESP32-S3: if a transient occurs between 3.6V (ESP's max limit) and 4.2V (TVS's Vbr), the TVS diode would not activate, and the ESP32-S3 could be damaged.

For example, a common Nexperia SOT-23-3 TVS shows:

• Vwm: 3.3V

• Vbr: 4.2V

• Vcl (Clamping Voltage): 3.3V (once it conducts, it clamps well, but only after Vbr)

My questions are:

• Is this "window of vulnerability" (e.g., 3.6V to 4.2V) an acceptable risk in a commercial product, given that most ESD events are much higher kV peaks that would trigger the TVS? Or is it a critical flaw that needs to be addressed?

• Are there practical, cost-effective, and PCB-fabrication-friendly solutions (i.e., not ultra-tiny CSP/WL-CSP packages, nor complex multi-LDO cascades) to reliably protect the ESP32-S3 within its 3.6V absolute maximum?

• Have I overlooked a specific type of TVS diode (e.g., a dedicated ESD protection diode with an extremely low Vbr/Vcl for 3.3V lines) or a combination of components (e.g., TVS + Zener) that would effectively close this "gap" without significantly increasing BOM cost or manufacturing complexity for a vendible product?

My current PCB uses 2oz copper and has a minimum trace/space rule of 0.25mm. Ultra-small packages like CSP1006-2 are very difficult to route and manufacture reliably under these rules.

Any insights or recommended parts/strategies from experienced designers would be greatly appreciated!
Thank you!

Not an EMC expert, but I'd imagine the Vcc line is a lot less sensitive to ESD than anything else, because as you say ESDs are generally fast transients; high voltage but not too much current and very short. You'd have to run the numbers, but I'm hafway sure the decoupling you should have anyway will be able to shunt the voltage away to ground easily.

I recognise the issue. Indeed, voltages that are this critical (3V3 is operating voltage, 4V2 is damage) aren't easy to protect using TVS diodes. Go too low and the TVS will be conducting, just a bit, but it will dissipate some current into heat. Go too hight and your device is pushing up the daisies on a power surge.

Two thoughts come to my mind:
- if you add a huge electrolytic capacitor, it will probably already cut off the highest voltage peaks.
- there a circuits (and even specific IC's) called a crowbar switch that can protect a power line within very precise limits. If have used one once to avoid overloading a string of LED's that would need a very precise voltage (before specific current controlled power sources where widely available). Their purpose is, like a TVS, to short circuit the power line whenever it goes over your specified limit. But you can alter the circuit (like I did) to just isolate the power supply instead.

Having said this, I have found the Espressif IC's to be quite tolerant to whatever you hand to them on their pins, having experience with them since 2015...