Introduction

In electronic devices, transient overvoltage events such as electrostatic discharge (ESD), lightning strikes, and surge voltages can instantly damage precision circuits. ESD diodes and TVS (Transient Voltage Suppression) diodes are two types of key protection components, and the selection should be based on the application scenario:

ESD diode: Mainly used for anti-static purposes, it has a certain surge protection capability and is suitable for static protection of signal interfaces, Vbus (USB bus power supply), VCC and other power supplies.

TVS diode: It is suitable for protection against surge voltages (such as lightning surges and switching transients), and is commonly found in industrial equipment (power supplies, communication equipment) and automotive electronics.

In a typical protection circuit, diodes are connected in parallel at both ends of the signal/power line and ground, as shown in the following figure:

In this article, the EMC guy from Leimao will assist engineers in quickly choosing the appropriate protection devices from three aspects: parameter analysis, selection steps, and case analysis.

The principles of ESD/TVS diodes

The protective diode needs to meet the following core requirements:

"No interference" during normal operation:

Reverse operating voltage (VRWM) : It must be higher than the peak value of the circuit's maximum operating voltage (VRWM≥ maximum operating voltage). For example, for a 5V circuit, devices with VRWM≥5V should be selected

Leakage current (IR) : At the maximum operating temperature (such as 85℃), IR must be lower than the allowable value of the circuit (μA or nA level).

Parasitic capacitance (CJ) : For high-frequency signal lines (such as USB 3.0), CJ<0.5pF is required.

2. "Precise clamping" during overvoltage:

Clamping voltage (VC) : It must be lower than the withstand voltage limit of the protected device (for example, if the chip withstand voltage is 10V, then VC≤10V).

Surge current (IPP) : Select the pulse type based on the application scenario, and then choose according to the pulse type and test level, referring to the test conditions of IEC 61000-4-2 (ESD) or IEC 61000-4-5 (surge).

Analysis and Selection Table of Key Parameters

Table 1: Reference for Voltage (VRWM) Selection

Table 2: Suggestions for Matching Capacitors (CJ) with Signal Types

Selection steps and case analysis

1. Determine the application scenarios: for consumer electronics, industrial equipment, or automotive electronics? Signal path or power path? Electrostatic protection or surge protection? What testing standards are required for surge protection? The requirements of PCB layout for packaging.

2. Parameter considerations: Operating voltage VRWM and temperature range TA, leakage current IR and capacitance CJ, clamping voltage VC and inrush current IPP.

Case 1: USB 3.0(Signal)ESD Protection for Mobile Phones (Consumer Electronics)

l Vbus power cord:

Model n: ESDA05CP (VRWM=5V, VC=10V, IPP=8A/8/20μs)

n verification: VC≤10V (lower than the chip withstand voltage of 15V), in compliance with ±15kV contact discharge and ±25kV air discharge.

l D+/D- data cable:

n Type selection: ULC0502P3 (CJ=0.6pF, IEC 61000-4-2 ±30kV air discharge);

n Verification: The data signal Cj of USB2.0 is ≤0.6pF, which does not affect the signal integrity.

l SSTX/SSRX high-speed signal line:

Model n: ULC0524P (CJ=0.3pF, IEC 61000-4-2 ±30kV Air discharge).

Case 2:12V DC power surge Protection

Select ESD/TVS devices with appropriate protection current based on the environment where the power supply is located. If the IEC61000-4-5 surge high-level test is required, high-power SMC devices should be chosen.

The secondary 12V DC power supply for consumer electronic devices can adopt ESD devices SD12C/SD1271P6W. They have a small package to save space and meet IEC61000-4-2, level 4, with contact discharge at 30KV and air discharge at 30KV. It also has a certain surge resistance capability as per IEC61000-4-5 (Lightning) 15A (8/20μs).

l Industrial equipment (such as PLCS, sensors, and power modules for communication base stations), dealing with lightning surge (8/20μs waveform), grid switching transients, and reverse electromotive force of switching power supplies, IEC 61000-4-5 (grades 1-4);

Operating voltage (VRWM) : It is generally recommended that the Vrwm of the TVS diode be greater than 1.2 times the power supply voltage. Choose 15V, such as SMBJ15CA, to avoid frequent false triggering of the TVS due to the voltage fluctuations of the power supply itself.

n Clamping voltage (VC) : It needs to be lower than the withstand voltage of the protected device. For example, if the withstand voltage of the DCDC at the back end is 40V, select VC≤40V. (If the working voltage and the withstand voltage range at the back end are narrow, there are back-bounce TVS devices available for selection. For example, for a 24V DC power supply with a withstand voltage of 35V at the back end, LM1K24CA, SMB package is small, low residual voltage VC=35V.) The protection level of a single chip can reach 2KV.

n Selection recommendation Leave sufficient protection margin, pay attention to increase heat dissipation measures in high temperature environment to prevent damage caused by overheating of TVS DIODE ‌. When necessary, multi-level protection can be adopted, with GDT discharging and amplifying the current and TVS precisely clamping. (Cascade order: GDT→TVS)

Case 3:12V Car Power Surge Protection

Unlike industrial power supplies, automotive power supplies have greater fluctuations and stricter test standards. They need to pass a series of tests in the ISO 7637-2/ ISO 16750-2 standard. The most stringent one in this standard is the Pulse 5A waveform and parameters as above.

Working voltage (VRWM) : For a 12V system, 24V devices (such as SMBJ24CA) are generally selected.

Clamping voltage (VC) : Lower than the withstand voltage of automotive electronic devices

Surge current: ISO 7637-2 pulse 5A (peak voltage 200V) and ISO 16750-2 load drop test

Temperature range: -40℃ to +125℃ (ECC-Q101 certified)

Summary and Suggestions

Selection priority: VRWM > VC > CJ (high-frequency scenarios);

l Scene adaptation

Consumer electronics: Low CJ + high ESD level (such as ±15kV contact discharge);

n Industrial equipment: High IPP (such as 200A surge), low clamping voltage VC;

n Automotive Electronics: Automotive-grade devices that comply with ISO 7637-2/ ISO 16750-2 standards and meet ACQ-101 certification requirements;

Key point: It is necessary to confirm that the parameters meet the standards through actual tests to avoid theoretical selection deviations.

Layout: The TVS lead length is ≤20mm, and the ground wire is directly connected to the power supply ground layer to reduce parasitic inductance.

Leimao Electronics has its own EMC laboratory and offers free preliminary tests. If you need any assistance, you can contact the Leimao EMC delivery person.

It is hoped that through the parameter analysis and case study of the EMC delivery guy from Leiditech, engineers can quickly locate the target devices and avoid system failures caused by improper selection. For further selection support, you can follow the official account of Leiditech Electronics to obtain various interface protection solutions or contact the Leimao EMC delivery person to get customized solutions.

Leiditech, also known as Lemao Electronics, 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. Lei MAO has an experienced R&D team that can provide personalized customization services based on customer needs and offer the best solutions to customers.