Feature description

Designed to protect submicron 3-V or 5-V, the SN65220 device is dual-supply, the SN65240 and

The circuits from the noise transient SN75240 device are four unidirectional transient voltage suppressors (TVS). these devices

Port ESD Protection Exceeds: Provides electrical noise transient protection for -15kV Human Body Model Universal Serial Bus (USB) low-speed and full-speed ports.

– The 35 pF input capacitance of the 2-kV machine model makes it unsuitable

For Hi-Speed USB 2.0 applications.

Available in WCSP chip scale package

Isolation Voltage: 6V (Min) Any cable I/O may be affected by electrical noise transients from various sources. these noises

Low current leakage: 1-µA max at 6V transient can cause damage to USB transceiver

Low capacitance: 35 pF (typ) and/or USB ASIC if they are of sufficient size and duration.

Electrostatic discharge performance of application SN65220, SN65240,

Measure USB full-speed hosts, hubs or peripherals and SN75240 devices on the system

Port level, in line with IEC61000-4-2. However, system design affects the results of these tests. Achieving a high level of compliance requires careful board design and layout techniques.

A Simplified TVS Current-Voltage Schematic

Typical characteristics TA = 25°C unless otherwise noted.

Transient Voltage Suppressor Current vs Voltage

Parameter measurement information

Leakage current measurement

Breakdown voltage measurement

Detailed description

Overview

The SN65220, SN65240 and SN75240 devices integrate multiple unidirectional transient voltage suppressors (tv). Figure 4 shows the equivalent circuit diagram of a single TVS diode.

For positive transients, only the Q1 transistor determines the switching characteristics. When the input voltage reaches the Zener voltage VZ, the Zener diode D1 conducts; therefore, the base-emitter voltage VBE is allowed to increase. At VIN=VZ+VBE, the transistor starts to conduct. Thereafter, its on-resistance decreases linearly with increasing input voltage.

For negative transients, only diode D2 determines the switching characteristics. Here, switching occurs when the input voltage exceeds the diode forward voltage VFW.

Functional block diagram

SN65240 SN65220 and SN75240

Air Conditioning Ground B, B, D

Feature description

The SN65220, SN65240 and SN75240 series of unidirectional transient voltage suppressors provide transient protection for USB low-speed and full-speed ports. These TVS diodes provide a minimum breakdown voltage of 6.5V to protect USB transceivers and USB asic and are typically implemented in 3-V or 5-V digital CMOS technology.

Device functional mode

TVS diodes have two functional modes of high impedance and conduction.

Under normal operating conditions, i.e. in the absence of high voltage transients, the breakdown voltage of the TVS diode will not exceed and the device maintains high impedance.

In the presence of high voltage transients, the breakdown voltage is exceeded. Then, the TVS diode conducts and becomes low impedance. In this mode, excess transient energy is shunted directly to the local circuit ground, preventing electrical damage to the USB transceiver.

Application and Implementation

Notice

The information in the application section below is not part of the TI component specification and TI does not warrant its accuracy or completeness. TI's customers are responsible for determining the suitability of parts for their purpose. Customers should verify and test their design implementation to confirm system functionality.

Application Information

Universal Serial Bus (USB) has become a popular solution for connecting PC peripherals. USB allows devices to hot-plug existing PC systems without restarting or shutting down the PC. Due to the attractive hot-plug capability of USB systems, there is frequent human-to-human interaction with USB systems, so large-scale ESD attacks and damage to critical system components are possible. ESD protection included on existing hardware is typically in the 2-kV to 4-kV range for the human body model (HBD) and 200-V to 300-V for the machine model (MM). ESD voltage levels found in normal USB operating environments can exceed these levels. The SN75240, SN65240 and SN65220 devices will enhance the robustness of existing USB hardware to ESD attacks common to environments where USB may be used.

typical application

Figure 5 illustrates a typical USB system and application of the SN75240, SN65240 and SN65220 devices. The D+ data line must be connected to pin A, the D- data line to pin B, and the existing ground line to the device ground to increase the amount of ESD protection provided to the USB port.

The suppressor is designed with an extremely low maximum current leakage of 1 μA, an extremely low typical capacitance of 35 pF, and an isolation voltage of minimum 6 V, the SN65220 device will provide additional protection to the USB system hardware during ESD events without introducing High capacitance and current leakage levels typical of external transient voltage suppressors. The addition of a SN75240, SN65240 or SN65220 device facilitates both full-speed and low-speed USB 1.1 bandwidth standards.

Detailed design procedure

To effectively protect the USB transceiver, use a TV diode with a breakdown voltage close to 6 V, such as the SN65220, SN65240, or SN75220 devices.

Since the TVS junction capacitance is 35 pF, these TVS diodes should only be used in USB transceivers with a maximum 12 Mbps full speed capability.

Place the TVS diode as close to the board connector as possible to prevent transient energy from entering further board space.

Connect TVS diodes between the data lines (D+, D-) and the local circuit ground (GND).

Since noise transients represent high-speed frequencies, ensure a low-inductance return path for transient currents by providing a solid ground plane and connecting the TVS terminal to ground using two vias.

Apply Curve

Power supply suggestion

Unlike other semiconductor components that require a supply voltage to operate, the SN65220, SN65240 and SN75240 transient suppressors are combinations of multiple pn diodes activated by transient voltages. Therefore, these transient suppressors do not require an external voltage supply.

Layout Guidelines

Multiple ground pins reduce connection resistance to ground. To improve circuit operation, connections to all ground pins must be provided on the system printed circuit board. If the equipment is not properly grounded, the speed and protection of the equipment will be reduced.

The ground termination pad should be connected directly to the ground plane on the board for best performance. A single trace-to-ground conductor will not provide an efficient path for fast rise time transient events including electrostatic discharge due to parasitic inductance.

The nominal inductance value of the PCB trace is approximately 20 nH/cm. This value may seem small, but apparently "short length" traces may be enough to produce significant L(di/dt) effects and fast rise time ESD peaks.

Mount the TV as close to the I/O socket as possible to reduce transient radiation, which is grounded.

Notice

The direct connection paths of the lines are brought to the suppressor mounting pads to minimize parasitic inductance in the inrush current conduction path, thereby minimizing the L(di/dt) effect.

layout example

USB via power ground plane

Via the power plane connector