3.3V power rail protection for esp32-s3 - Page 1
Forum section: electronics / projects

author: Ferrita
author_rank: Contributor
timestamp: July 28, 2025, 04:07:34 am
content: Hello everyone,I'm designing a PCB for a commercial product using an ESP32-S3, and I'm facing a challenge with its3.3V power rail protectionagainst ESD and other fast transients.Here's the core issue:TheESP32-S3has a very strictAbsolute Maximum Rating for its VDD33 power supply of 3.6V.My PCB's main power rail is3.3V, regulated by an LDO.I'm looking for an appropriateTVS diodefor 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 suitableTVS diodesI'm finding (e.g., Nexperia SOT-23-3, 1- or 2-channel, some bidirectional options exist) have aWorking Voltage (Vwm) of 3.3V.However, theirBreakdown 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 between3.6V (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: 3.3VVbr: 4.2VVcl (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) anacceptable riskin 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 therepractical, 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 acombination 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!

author: Georgy.Moshkin
author_rank: Frequent Contributor
timestamp: July 28, 2025, 05:37:54 am
content: I think the best solution is to use protection chips designed for USB. For example, USBLC6. Despite their design optimized for 5v, I would not be surprised if they provide better protection than custom design for 3.3v. I've used USBLC6 to protect DAC outputs of 3.3v MCU connected to external equipment through coaxial cable which is often exposed to static electricity. Plus, it protects 3.3v power rails against >5v transients. Reduced components count (same chip on USB port). Note that this is my naive solution, but I think it works well: I do not have MCU freeze/reboots when connecting to external equipment. It was common in my older signal generator without USBLC6 on DAC output.

author: David Hess
author_rank: Super Contributor
timestamp: July 28, 2025, 07:50:50 am
content: If you need that kind of protection, a TVS diode is not suitable for the reasons you identify. Some type of shunt protection circuit with a much tighter voltage tolerance is required. Usually the capacitance on the output of the regulator is enough for ESD protection.

author: xvr
author_rank: Frequent Contributor
timestamp: July 28, 2025, 11:16:02 am
content: QuoteThis is something like miracle. Can you share this TVS type with us? General TVS has Vcl a order of magnitude more than this.

author: Ferrita
author_rank: Contributor
timestamp: July 28, 2025, 02:45:30 pm
content: Hi xvr,Thank you again for your sharp eye and valuable insight! It led me to re-examine the datasheet very closely, and you were absolutely right to question the Vcl; it helped clarify things immensely.The specific TVS diode I was referring to is theNexperia PESD2USB3UXT-QR. Its datasheet indeed specifies a Vcl (Clamping Voltage) of 3.3V at IPP = 8A, measured under TLP conditions (tp = 100 ns; ANSI / ESD STM5.5.1-2008). It appears this part is specifically designed as an ESD protection device with a very tight clamping performance, which is fantastic for my ESP32-S3's strict 3.6V absolute maximum rating.My Proposed Full Protection StrategyGiven the ESP32-S3's sensitivity and the "window of vulnerability" (3.6V to 4.2V Vbr) that even this excellent TVS presents for slower/sustained overvoltages, I'm now considering a combined approach:Primary ESD/Fast Transient Protection: Using two of these Nexperia PESD2USB3UXT-QR diodes connected in a "back-to-back" configuration to provide robust bidirectional ESD protection on my 3.3V power rail. Its low 3.3V clamping voltage is ideal.Complementary Overvoltage Protection: Adding a 3.6V Zener diode (e.g., onsemi BZX84C3V6L) in parallel with the TVS. The Zener's role would be to shunt current if the voltage slowly or moderately rises to 3.6V, acting as a "secondary safeguard" for scenarios that might fall below the TVS's 4.2V Vbr but still exceed the ESP32-S3's 3.6V limit.The Zener would protect against those "slower" overvoltages that the fast TVS might not immediately address in its breakdown region, or simply as an additional layer of security. Both components would be in easy-to-route SOT-23-3 packages.Does this combined TVS + Zener strategy make sense for providing comprehensive protection in a commercial product, balancing reliability with manufacturability and cost? Any thoughts on this approach would be greatly appreciated.Thank!

author: langwadt
author_rank: Super Contributor
timestamp: July 28, 2025, 02:48:50 pm
content: why do you think you need protection on the 3.3V?

author: xvr
author_rank: Frequent Contributor
timestamp: July 28, 2025, 03:40:52 pm
content: QuoteVery strange device. Vcl stated in datasheet as 3.3V, but in Fig 3 Vcl is a much larger than Vbr, that stated 8V at max.Also, in Fig 10 and 11 Vcl is 150V (on 8KV ESD pulse)I wouldn't count on it.QuoteThis doesn't make sense. TVS itself is a zener (very specific, but still zener)

author: Ferrita
author_rank: Contributor
timestamp: July 28, 2025, 03:58:32 pm
content: Hi Langwadt, excellent question!The quick answer is that I'm learning because I have little experience and rely on the advice of the AI.I'm a programmer and have always been interested in electronics. As a hobbyist, I even made a personal invention using development boards. It's a popular invention, appealing, so I considered making it a reality (maybe it's just a dream).Now I have a beautiful oscilloscope, a power supply, and a multimeter, and I'm taking the step of building my first circuit without development boards.I have no experience or training in electronics, so I need help from the AI. Sometimes it gives me very good advice, and other times I find its advice is theoretical and not practical, especially considering the cost of developing a PCB to try to sell.If I get a solid and reliable PCB, I have to pass the certifications, and that's where the AI helps me the most. I don't know anything about certifications.I don't know if protecting the 3.3V output line of an LDO (LD29150DT33R), powered by a switching power supply (5V-80A), with TVS diodes and a zener diode makes sense or is theoretical overkill.To be honest, I also don't know if I need 6 capacitors at the circuit input, an inductor plus 3 capacitors, plus the 4 LDO capacitors, but the AI advises me to add a TVS diode and a zener diode to protect those 3.3V. It tells me it's a good strategy for certification and to reduce errors in "supposed" returns if I ever manage to market it.Maybe I'm creating an electronic Frankenstein

author: xvr
author_rank: Frequent Contributor
timestamp: July 28, 2025, 04:05:17 pm
content: QuoteThis is a question that you should start from, not ESD protectionWhat kind of PCB are you making?Will it be used as part of another device?Will it be powered externally (or from another PCB within the same device)?Will its inputs, outputs and power be accessible from the outside?

author: jc101
author_rank: Frequent Contributor
timestamp: July 28, 2025, 04:07:14 pm
content: What is the power source?Is it connected to anything else, or nicely self contained in a box?Edit: I see @xvr has already asked the pertinent questions.I am just doing a design with an ESP32-S3, it's USB powered. With a specific TVS for USB ESD protection before the LDO is all I'm planning on initially. I've never had anything downstream of an LDO take a hit during EMC/ESD testing, providing the inputs have good protection at the point of entry.

author: Ferrita
author_rank: Contributor
timestamp: July 28, 2025, 04:19:13 pm
content: Your answer has brought reality home to me. By showing me the images, I've now been able to verify that the specifications use ideal values and can "fool" inexperienced people like me. It's a good lesson.I think I'll use a common 3.6V Zener diode.Thank you for your time and attention!

author: Ferrita
author_rank: Contributor
timestamp: July 28, 2025, 04:44:38 pm
content: What kind of PCB are you making?I'm designing the power supply for a board that will include Bluetooth connectivity and frequency analysis for sound (which is why I use so many capacitors to avoid noise), intended for LED lighting.Will it be used as part of another device?Yes, it will be integrated into a custom housing as the main control unit of the luminaire.Will it be powered externally (or from another PCB within the same device)?It will be powered externally via a switching power supply accepting 5V DC from a wall adapter. This 5V then feeds an LDO that provides 3.3V to the board.Will its inputs, outputs and power be accessible from the outside?The only external part will be the power cable that runs to the wall. The circuitry is enclosed in an enclosure, as are the LEDs. The user has no access to the circuitry or any sensitive parts. I don't know if I'll need to use an external antenna for Bluetooth.Thank you all for your interest

author: Ferrita
author_rank: Contributor
timestamp: July 28, 2025, 04:56:12 pm
content: For the testing phase, I've included terminal blocks so I can have several individual PCBs (ESP32-S3, two Bluetooth modules, etc.). These terminal blocks will disappear in the final design. It's a 4-layer PCB (two ground and one 3.3V) made of 2oz. Many capacitors are used to mitigate the noise introduced by the power supply (5V-60/80A) to ensure the best possible audio analysis.I'm going to replace the "CSPSBULC3V3LB-TP" TVS diode with a common 3.6V Zener diode.Pcb:https://imgur.com/a/Lo9jr5D

author: xvr
author_rank: Frequent Contributor
timestamp: July 29, 2025, 03:42:53 pm
content: QuoteThis means that the ENTIRE PCB (not just the power supply) needs to be certified. Bluetooth inside is a very bad thing. It means that your device is an "intentional radiator" and you MUST have it certified by a "certification body" and that costs a lot of $$$.QuoteA custom enclosure does not turn your PCB into a separate module, so all the responsibility for protection (and certification) falls on your PCB.QuoteThis is good - at least you should not include in certification 'mains powered device'QuoteCan you install this LDO in you PCB? (I think so, because you have only one PCB in housing, as I understand). ESD protection of input 5V (to LDO) is much simpler, than the protection of 3.3V for ESP32.If 3.3V voltage will not be released to the outside, ESD protection is not needed.QuoteThen the only protection you'd need would be on the input connection of that power cable.QuoteLEDs can be sensitive part for ESD protection. Electrostatic discharge through the LED housing can penetrate into the device.

author: Ferrita
author_rank: Contributor
timestamp: July 29, 2025, 11:25:21 pm
content: Thank you very much for taking the time to review my inquiry and for your valuable feedback. I greatly appreciate your detailed comments.You've highlighted some critical points that are definitely top of mind for me, especially regarding certification and ESD protection.Regarding Bluetooth certification, you are absolutely correct. My initial message may have been unclear, but I am actually using a pre-certified Qualcomm QCC3083 module. This module comes with its own integrated antenna (although I don't know if it will be sufficient) and has already passed the necessary RF/EMC certifications. I understand that this significantly simplifies the final product certification process, as it eliminates the need to certify my PCB as an "intentional radiator" from scratch.Your comments regarding ESD protection for LEDs are also very insightful and a crucial concern. My invention can be touched by people; we like to touch things that glow, even though they don't require human contact to function. Therefore, the physical design of the enclosure poses a major challenge for me.The entire circuit, including the LEDs, will be completely isolated from the user within a robust enclosure. The power cable connects internally to a power supply, and the 5V line for my PCB is also isolated. My goal is to design the enclosure to be robust and prevent any direct contact with the LEDs or internal electronics. This includes ensuring adequate creepage and safety distances to prevent static discharges from leaping from the external surface to the internal components. Your comment reinforces the importance of this aspect of mechanical design to prevent static charges.Thanks again for your feedback. It really helps me refine my design strategy and consider all potential challenges.I'm in a constant learning phase, and thanks to these forums and people like you, I can learn and feel more confident.Thanks, xvr!

author: Ferrita
author_rank: Contributor
timestamp: July 30, 2025, 12:25:41 am
content: In light of the information I've received, reviewed, and compared, my decision was to eliminate the two TVS diodes and use Zener diodes with tolerances set to 2% (PDZ3.6B.115 and BZT52H-B5V6.115).I don't know if it's the best option, but with the knowledge I have today, I believe it's a valid solution.Thanks to everyone!

author: GigaJoe
author_rank: Frequent Contributor
timestamp: July 31, 2025, 01:45:22 am
content: can be zener (consider zener power dissipation for a long time, when VR fail , as in this case zener will feed circuit for a long time, or you complicate schematic to measure V per stm , and signal on overvoltage) ,or overvoltage crowbar circuit.add diode for polarity protection