ESP32 Incorrect VIN Pin Usage

Common Causes

⚠️
Supplying Voltage to VIN Without Regulation
Feeding raw voltage to VIN without understanding its path through onboard regulators can cause overvoltage or excessive heat, damaging the board.
🔁
Drawing Too Much Current from VIN
Using VIN to power external modules like servos or displays can overload the USB power source or onboard regulator, causing resets or brownouts.
🔌
Confusion Between VIN and 3.3V Pins
Miswiring 3.3V into VIN or vice versa can bypass or overload the voltage regulator, leading to boot failures or permanent board damage.
🧯
Reverse Current Path via VIN
Supplying power to both USB and VIN simultaneously without proper isolation may cause current backflow and damage to host ports or the board.

Symptoms

ESP32 Overheats or Smells Hot

Board becomes hot to the touch shortly after power-up, even without Wi-Fi or peripherals active.

Frequent Resets or Boot Loops

The board keeps rebooting or fails to start code execution when powered via VIN.

Brownout Detector Was Triggered

Serial output repeatedly shows: Brownout detector was triggered

No Boot When Powered from VIN

Board only boots when connected via USB, not when powered through VIN, indicating regulator issues.

Solutions

Understand Your Board’s Power Path

Check the schematic or datasheet to see if VIN is input to a 3.3V regulator or directly tied to USB 5V. Never exceed the input voltage range.

Limit Current Draw on VIN

If you’re drawing more than ~500mA from VIN to power external devices, consider using a separate power supply and isolating it from ESP32’s USB input.

Don’t Mix VIN and 3.3V Pins

VIN (or “5V”) and 3.3V are not interchangeable. Supplying 3.3V to VIN may not boot the board, and applying >3.3V to the 3.3V pin can damage the ESP32.

Use Diodes for Power Source Isolation

When powering from both USB and VIN, add Schottky diodes to prevent reverse current that could damage components.

More Details

ESP32 Incorrect VIN Pin Usage #

The VIN pin — sometimes labeled as "5V" or "RAW" — can be a source of confusion and frustration for ESP32 users. While it offers a convenient way to supply power to the board or tap into available voltage, improper use of this pin can result in boot failures, unstable behavior, or even permanent damage to your board.

This guide explains how VIN works, common mistakes, and how to power your ESP32 correctly.

What Is VIN on ESP32 Boards? #

The VIN pin is typically the input to the onboard voltage regulator. On most ESP32 DevKit and NodeMCU boards, VIN is directly connected to the USB 5V line. It provides a convenient way to power the board if you're not using USB, or to tap into the USB power line to supply external modules like sensors or relays.

But here's the catch: VIN is not regulated. Supplying incorrect voltages or drawing too much current from it can cause:

Regulator overheating
Brownouts during Wi-Fi activity
USB host damage from reverse current

Common Misuses and Their Effects #

🔥 Supplying Incorrect Voltage #

Many assume they can feed any voltage into VIN. But most boards expect 5V regulated input on this pin. Supplying more than 6V (or even 5.5V) can overwhelm the regulator, while voltages below 4.5V may not provide enough headroom for stable 3.3V output.

Brownout detector was triggered

...or just remain dark with no boot.

🔁 Drawing Excess Current for Peripherals #

It’s tempting to power servos, displays, or LED strips from VIN. But since VIN is often tied to USB, this current comes from your computer or USB charger. Drawing more than 500mA can cause:

USB port resets
ESP32 reboot loops
Serial disconnects mid-flash

⚠️ Confusing VIN with 3.3V #

Supplying 3.3V to VIN (instead of the proper 3.3V rail) bypasses the regulator and may leave the ESP32 underpowered. Conversely, sending 5V into the 3.3V pin can destroy the chip instantly.

Symptoms:

ESP32 only boots when USB is used
No serial output or LED activity
Sudden overheating or burnt smell

🔃 Dual Power Without Isolation #

If you connect USB and an external supply to VIN simultaneously, you risk creating a reverse current path. Without a blocking diode, this may damage your PC’s USB port or the board’s onboard regulator.

How to Use VIN Safely #

✅ Supplying Power via VIN #

Use a clean, regulated 5V supply to power the ESP32 via VIN. Check your board’s datasheet or schematic to confirm the voltage range (typically 4.5V–6V). If you're unsure, use USB power instead.

✅ Powering External Devices from VIN #

If you're drawing from VIN to power peripherals, make sure the total current draw stays below 500mA if powered by USB. For larger loads, use a separate 5V power source — and ground it to the ESP32.

✅ Isolate Power Sources #

When switching between USB and external power, use a Schottky diode on the VIN input to prevent reverse current. Alternatively, use jumper headers or switches to choose between power sources manually.

✅ Never Feed VIN into 3.3V Pins #

Use proper level shifting or voltage regulators if your external source is not 3.3V. Never "step down" voltage by connecting it to the wrong ESP32 pin — that's a recipe for disaster.

Conclusion #

VIN is a helpful feature — when used correctly. Misunderstanding how it interacts with the rest of the board's power circuitry is a leading cause of unexplained reboots, brownouts, and dead boards.

Double-check your wiring, mind the voltage levels, and never assume two boards have the same VIN behavior. When in doubt, use the USB connection and let the onboard regulator do its job.