Introduce the requirements of TVS for ESD protection of several common handheld devices

Audio input/output: The signal rate of the audio circuit is relatively low, and the requirements for device capacitance are not too high. Around 100pF is acceptable. Some designs combine headphones and microphones together, while others have separate circuits

In this case, a single TVS can be chosen, while in the latter case, if two circuits are adjacent, a multi-channel TVS array can be used, and only one device can be used to protect both circuits.

Buttons/switches: The data rate of these circuits is very low, and there are no special requirements for the capacitance of the devices. Ordinary TVS arrays can handle it.

Data video/USB 2.0: The data rate can reach up to 480Mbps, and some videos have a data rate of over 1G. Therefore, low capacitance LCTVS should be selected. It usually involves connecting a low capacitance diode in series with the TVS diode to reduce the capacitance of the entire circuit (which can be lower than 3pF) and meet the requirements of high-speed circuits.

SIM card/antenna: There is a device specifically designed for this type of port that integrates ESD (TVS)/EMI/RFI protection into one chip, fully reflecting the infinite integration solution of chip devices.

Power supply/charging port: As it is a DC circuit, high capacitance devices can be used. This port may be subject to high-energy impact, and devices that integrate TVS and overcurrent protection functions can be selected.

When selecting devices for different purposes, it is important to avoid operating them near their design parameter limits. Devices with fast response times and high sensitivity should also be selected based on the characteristics of the protected circuit and the potential to withstand ESD shocks

This is crucial for effectively utilizing protective devices, and devices that integrate other functions should also be considered first.

Many semiconductor manufacturers offer various forms of TVS diode packaging, especially micro packages such as SOT23 and SC-70, as well as flip chip packages of the same size as chips. They only occupy about 4.8mm2 on the board, but can

Simultaneously protecting multiple lines. Recently, many new products have been adapted to the high integration and miniaturization requirements of portable devices. Integrating EMI/RFI/ESD protection into one device not only effectively reduces space, but also greatly reduces costs, lowers device procurement and processing costs. For ports that require both protection functions, it can be considered the first choice for designers.

PCB layout coordination

For portable devices, the increasing complexity and precision of various integrated circuits make them more sensitive to ESD, and the previous universal circuit design is no longer suitable. While using TVS diodes to protect against ESD damage, it is necessary to

Cooperate with a reasonable PCB layout.

Firstly, it is important to avoid self perception. For sudden and drastic pulses like ESD, it is likely to cause parasitic self inductance in the circuit, resulting in strong voltage surges that may exceed the IC's tolerance limit and cause damage. Load generation

The self induced voltage is directly proportional to the intensity of power supply changes, and the transient characteristics of ESD impact are prone to induce high self induction. The basic principle for reducing parasitic self inductance is to shorten the shunt circuit as much as possible, taking into account the grounding circuit, TVS, and protected circuit

All factors including the circuits between lines and the pathways from interfaces to TVS. So TVS devices should be as close as possible to the interface and the protected line, in order to reduce the chance of self inductance coupling to other adjacent lines.