An electrochemical gas sensor is a device that measures the concentration of gases by detecting the current signal generated from the oxidation or reduction reactions of the target gas on the electrode surface. It plays a crucial role in industrial safety, environmental monitoring, indoor air quality assessment, and portable gas detection equipment.

The core principle is as follows: The target gas undergoes oxidation or reduction reactions on the electrode surface under constant potential control. The generated current is proportional to the gas concentration, thereby converting the gas concentration into a measurable electrical signal.

Take the Alphasense CO-AX carbon monoxide sensor as an example. Its typical applications include industrial safety monitoring and home gas leakage warning. The measurement range is 0 - 2000 ppm, with a sensitivity of approximately 50 nA/ppm. The core circuit of this sensor is: U3 sensor with three electrodes (WE/CE/RE) is connected to the constant potential control module. The nA-level reaction current is converted into a voltage signal by a transimpedance amplifier, which is then sent to the MCU for processing. A LDO is provided to supply a stable power supply.

                                                                               配图来自ADI

Leiditech's Guide on Electrostatic Surge Protection for Electrochemical Sensor Circuits

1. Sensor interface（WE/CE/RE）

The parallel low-capacitance ESD (Leiditech SD05C) features bidirectional protection, which is suitable for the three-electrode signal range. With a low capacitance of 11pF, it can reduce the attenuation of nA-level weak current signals, ensuring that the clamping voltage is within 13V under IEC 61000-4-2 level 4 (contact discharge ±8kV, air discharge ±15kV) testing, which is lower than the power supply withstand voltage limit of the subsequent ADA4505-2 operational amplifier.

2. Constant potential control module and transimpedance amplifier

The feedback network of the transimpedance amplifier (with a 100kΩ resistor) is recommended to be paralleled with ESDA05CC (in SOD-523 package). A 39pF capacitor is matched to the circuit's reactance characteristic. With a 20A current capacity, it can handle sudden surges and protect the high-impedance feedback node from being electrostatically damaged.

3. Signal output terminal and interface with MCU

l After the sensor signal is amplified and connected to the MCU (such as the AIN1± pins of AD7798), it passes through an RC filter network (1kΩ + 100pF) with a cutoff frequency of 1.6MHz, which is suitable for the bandwidth of the sensor signal (≤10Hz). At the same time, it is connected in parallel with ESDA33CP30 (3.3V) or SMDA05CCN (5V), both of which meet the IEC 61000-4-2 level 4 protection requirements.

The UART interface (RXD/TXD) of the MCU adopts ESDA33CP30 (3.3V) or ULC0542C (5V), providing bidirectional protection signals. With low junction capacitance, it is compatible with serial communication rates up to (≤115200bps), ensuring that data transmission is not affected by the protective components.

4. Power module

An TVS device is added at the 12V power input to resist grid surges.。

For VCC 3.3V, Lebao uses ESD0321CW (DFN0603 package, 30pF capacitor, 21A discharge current); 

For VCC 5V, Lei Ma uses PTVS0542H100 (DFN1006 package, 105A) to reduce power supply ripple and electrostatic interference.

Leiditech is committed to becoming a leading brand in electromagnetic compatibility solutions and component supply, offering products such as ESD, TVS, TSS, GDT, MOV, MOSFET, Zener, and inductors. Leiditech has an experienced R&D team that can provide personalized customization services based on customer needs, offering the best solutions to customers.