Part Number Selection Guide: Shanghai Leiditech Electronics Low Capacitance Multi-channel ±15kV ESD Protection Array - Comprehensive Analysis

A、Overview

Shanghai Leiditech Electronic: The ULC0542T/SR05/USRV05-4/ULC0524P series is a low-capacitance ESD protection diode array specifically designed for high-speed data interfaces. Its core function is to protect sensitive electronic equipment on communication lines from damage caused by electrostatic discharge (ESD) and transient voltages. It also takes into account electrostatic protection and high-speed signal transmission. It is one of the core product lines of Shanghai Leiditech Electronic in the field of ESD protection.

Core features and advantages

• ULC0542T features a dual-channel ESD protection structure and can be used for high-speed signals such as Gigabit Ethernet, USB 3.0, and HDMI;
• SR05 is a three-channel device, suitable for USB 2.0 applications, providing both 2-channel I/O and Vbus support;
• USRV05-4/ULC0524P has an ultra-low junction capacitance 4-channel design. A single chip can protect four channels of I/O and can be used for the protection of 100/1000 Mbps networks, digital/analog video interfaces, SIM card interfaces, LVDS interfaces, etc.
• Electrostatic Discharge (ESD) protection capability: The ESD diodes produced by Shanghai Leiditech Electronic all comply with the IEC 61000-4-2 standard, corresponding to the domestic standard GB/T 17626.2. They can withstand ESD pulses of ±15kV for the human model, ±8kV for contact discharge, and ±15kV for air discharge. The protection level reaches IEC 61000-4-2 Level 4. This protection level can meet the static protection requirements of the vast majority of industrial and consumer electronics.
• Electrical performance: ULC0542T (dual channel): Typical Cj = 0.8pF; USRV05-4/ULC0524P (quad channel): Typical Cj = 0.6pF (suitable for high-speed data transmission), the maximum leakage current is 1nA, the power supply voltage range is wide (suitable for +0.9V to +5V), and the low junction capacitance and low leakage current are the key to ensuring distortion-free transmission of high-speed signals;
• Encapsulation and environmental adaptability: Shanghai Leiditech Electronic provides ultra-small size packages such as 3-pin DFN1006-3 (1mm×0.6mm), 4-pin SOT143 (2.4mm×2.9mm), 6-pin SOT-26 (2.8 mm × 2.9 mm), and 8-pin SOP-08 (5mm×6mm). The operating temperature range is -40°C to +85°C, the storage temperature range is -55°C to +150°C, and it supports lead-free/RoHS compliance requirements.

B、Application

Ÿ   High-speed data interface: USB 2.0, USB OTG, FireWire, Ethernet

Ÿ   Video devices: SVGA video connection, various video transmission terminals

Ÿ   Mobile terminals and communication devices: Mobile phones, portable electronic devices

Ÿ   Other sensitive electronic devices: High-speed I/O interface scenarios requiring ESD protection

The low-capacitance multi-channel ESD protection array of Shanghai Leiditech Electronic, with its outstanding protective performance and compatibility for high-speed transmission, has been widely applied in these fields and has become the preferred protection solution for many electronic equipment manufacturers.

C、Working principle and protection mechanism

1. Structure

Each channel of the multi-channel protection device is composed of a pair of diodes. The ESD current pulses are directed to GND through the diodes, working in conjunction with the device's inherent ESD protection to limit the ESD peak voltage: ±25V for the human model, ±30V for contact discharge, and ±30V for air discharge.

2. Clamping voltage calculation

·         Ideal circuit: Forward ESD pulse VC = VCC + VF; Reverse ESD pulse VC = -VF (VF is the forward voltage drop of the diode)

·         In practical applications (taking into account parasitic inductances L1/L2/L3), the influence of line parasitic series inductance needs to be considered (as shown in the above figure). At this time, the clamp voltage formula is corrected as follows:

o    For forward ESD pulse: VC = VCC + VF (D1) + (L1 + L2) × d (IESD) / dt

o    For reverse ESD pulse: VC = - [VF (D2) + (L1 + L3) × d (IESD) / dt]

In the above formulas, IESD is the ESD current pulse, and L1, L2, and L3 are parasitic inductances.

3. Current characteristics of ESD events

Leiditech EMC team reminds that in an electrostatic discharge (ESD) event, the current pulse rises from 0 to the peak value within a nanosecond time (as shown in the figure above). For example, in a 15kV IEC-61000 air discharge ESD event, the pulse current will rise to approximately 45A within 1ns (the current change rate di/dt = 45×10⁹), and the inductance will cause an additional 450V increase in the clamping voltage. Even with a 10nH inductance corresponding to a 0.5-inch (12.7mm) circuit board trace, if there is parasitic inductance caused by unreasonable wiring, the actual clamping voltage on the protected signal line will be significantly increased. Regardless of the specified diode clamping voltage of the device, if there is parasitic inductance due to unreasonable wiring, it will significantly increase the actual clamping voltage on the protected signal line.

4. Requirements for bypass capacitors

A 0.1μF capacitor with low equivalent series resistance (low ESR) must be used between VCC and GND. This bypass capacitor can absorb the charge transferred during ±8kV IEC 61000 contact discharge ESD events.

Ideally, the power rail (VCC) can absorb the charge generated by the positive ESD shock without changing the regulated output. However, in reality, all positive power rails of the power supply have an effective output impedance. If the effective output impedance of the power supply is 1Ω, according to Ohm's law, the clamp voltage will increase according to the formula V = I * R. For example, a +8kV IEC 61000-4-2 ESD event will generate a 24A current spike. At this time, the clamp voltage will increase by VC = 24A * 1Ω = 24V. Leiditech EMC team emphasizes an unreasonable layout without a proper bypass design will further raise the clamp voltage, seriously affecting the protection effect, and this is also a common cause of protection failure in practical applications.

D、Application Design PCB Layout Suggestions:

Based on the years of practical ESD protection experience of Shanghai Leiditech Electronic and the professional summary by Leiditech EMC Team, the following are key PCB layout suggestions for application design, which can maximize the protective performance of the ESD protection array:

1. Shorten the wiring length between the connector or input terminal (I/O terminal) and the protected signal line;

2. Use separate power layer and ground layer to reduce parasitic inductance and decrease the impedance of ESD current flowing to the power rail;

3. Ensure that the return path of ESD transient current to GND and VCC is as short as possible;

4. Minimize the conductive power loops and ground loops;

5. Do not place critical signals near the PCB edge;

6. Parallel a low ESR ceramic capacitor between VCC and GND, and the capacitor should be as close to the VCC pin as possible;

7. Also, parallel a low ESR ceramic capacitor between the power supply terminal of the protected device and GND, and the capacitor should be as close to the power supply pin of that device.

Leiditech EMC team reminds that when selecting a Part Number, it is necessary to combine the actual application voltage level, channel number, interface type and PCB packaging space, and precisely match by referring to the above material number table. At the same time, strictly follow the PCB layout suggestions to achieve efficient and reliable ESD protection. Shanghai Leiditech Electronic can also provide professional selection support services to help customers avoid common mistakes in high-speed interface protection.