原创 Leiditech ESD protection introduction

 2013-9-3 14:02  710 8 8 分类: 消费电子

Leiditech ESD protection introduction

Here we discuss the ever-increasing need for electronic static discharge protection in today’s rapidly expanding mobile devices market. With this in mind, the circuit protection division of Leiditech inc. has been focused on providing circuit protection solutions. Whether, the end application is an antenna interface Ethernet router or USB data port on portable electronic products, Leiditech’ portfolio of overvoltage and over current protection products provides a solution for the application.

Leiditech offers three different technologies in its line of ESD protection products:

1) transient voltage suppressor diodes utilize avalanche breakdown of the silicon diode, in discrete or array configurations

2) ESD suppressor products use multilayer varistor technology with options of discrete or array configurations and

3) Schottky diodes implement a “rail-to-rail” clamp technique, in either discrete or array configurations, and can provide the necessary ESD protection.

ESD protection products are necessary to protect against ESD transient entering the system or device which will damage or destroy the electronics. The end application for ESD protection products are broad, ranging from Telecom, Consumer, Medical, Industrial and Computing. With every electronic human interface port or connector considered a possible entrance for ESD transients into the downstream circuitry of a system or device, the requirement for ESD protection will be large. On the back of the typical set-top box, shown here, the wide variety of interface ports that will require ESD protection products can be seen. For these USB, Firewire 1394, Ethenet and HDMI ports, ESD protection is required to limit product damage and increase the robustness of the equipment.

Human body ESD voltages are nature determined can be reached 15KV or more which will damage the IC. The key to selecting overvoltage protection is to consider what the equipment needs to be protected against. Therefore, it is practice to protect all “people interactive” data ports to limit the product damage and increase the robustness of the equipment. The external ESD protector then becomes the first lever of ESD protection with the IC providing residual second lever protection in the design.

The international Electro-technical Commission (IEC) developed a human body model (HBM) ESD event that would allow designers to design adequate protection into their electrostatic applications. The IEC defined the ESD discharge impulse with a rise time of less than 1ns and decay times of 60ns designed four levels of protection. IEC 61000-4-2 specifies HBMs up to 8 KV contact for ESD incursions that would be considered in portable equipment. IC protection with a level 1 specification will become secondary protection scheme where a primary protector is required against 8KV impulses. It is therefore important to ensure the IC or circuit being protected can support this peak voltage.

The most common method for ESD protection is to use small silicon-based transient voltage suppressor(TVS) diodes in avalanche breakdown mode as the first level of protection against ESD.

A wide range of working peak operating voltages is available in unidirectional or bidirectional configurations, arranged in discrete or array packages. TVS diodes provide ESD protection per IEC 61000-4-2 while their enhanced construction can provide additional electrical fast transient (EFT) and surge protection to the IEC 61000-4-4 and IEC 61000-4-5 standards respectively.

Leiditech offers ESD suppressor products using ceramic technology as an alternative ESD protection solution. The ESD Suppressor has a threshold voltage increase where the initial resistance is high. As the voltage increases, the resistance reduces with a resultant exponential increase in the current through the device. This allows the overvoltage disturbance to be shunted away from the circuit it is protecting while the energy is dissipated in the protector. Once the electrical disturbance has passed, the ESD suppressor will return to its high-resistance off-state. The technology provides an ultra-low capacitance 0.05pf maximum rating which makes them very attractive for high speed applications.

Some designs prefer to use a “rail-to-rail” clamping technique for ESD protection and Leiditech can satisfy this scheme with discrete or array schottky diode solutions. Using the Vcc line as positive and the Gnd, or Vdd, lineas negative, ESD transients on data lines can be diverted to either the positive or negative rail. A range of Schottky/Steering diodes are available in discrete and array SMT packages that would be ideal for this application.

The USB(Universal Serial Bus) specification provides a platform to allow a single USB port to drive up to 127 USB peripherals from a single host termination (PC). USB also allows remote powering from a broad range of low power after-market accessories including travel lights, mobile phone chargers, and laptop backup hard drives not requiring their own power supplies. USB 1.1 provided data transfer rates of up to 12 Mbps while USB 2.0 provided data transfer rates up to 480Mbps.

In a USB 2.0 application, the overvoltage protection can be provided using a 5V low capacitance TVS diode such as ####### or a 0.5pf ESD suppressor such as the #######.

Alternatively, the use of a steering diode array with ####### is another possible solution using a “rail-to-rail” clamp technique to the Vcc rail and ground. To meet the USB 2.0 overcurrent protection requirement for self-powered hubs and hosts, the use of a Leiditech such as the #####or ###### would be an ideal solution. In this example when the PPTC resettable fuse trips on over-current, it removes or reduces the current to all the affected downstream facing ports.

For applications that provide 2*USB ports, then the SRV05-4 device using integrated technology, can provide a more cost-effective manufacturing solution.

The new USB 3.0 standard was released in Nov 2008. New higher speed transfer rate of 5Gbps and higher 900Ma current limiter on Vbus will be required. The USB 3.0standard requires for additional data lines. The super speed of 5Gbps will still require ESD protection solutions but with a lower capacitance rating. Shown here a Leiditech circuit protection products that will meet the new USB 3.0 standard.

For applications that provide 2*USB 3.0 ports, the ######## device using integrated technology can provide a more cost-effective manufacturing solution.

The High-Definition Multimedia Interface(HDMI provides for transmitting digital television audiovisual signals from DVD players, set-top boxes and other audio visual sources to television sets, projectors and other video displays. HDMI can carry all standard and high definition consumer electronics video formats. It also can carry control and status information in both directions.

The HDMI connector has a pin that allows the source to supply +5.0V and 55mA minimum to the cable and sink. With high-speed communication on the 8 data lines, ESD protection with ultra-low capacitance is required.

ESD Protection solutions can include a discrete package option suing the ####### with a minimum 0.05 pF or alternatively, array solutions shown here using ######## ,making them ideal for meeting the requirement.

While TVS diodes are a popular choice for voltage clamp protection, their capacitance in Ethenet applications can hinder performance. To overcome this problem for high-speed communication ports, TVS diodes are used within bridge diode networks as shown here.

The trade-off with this arrangement is an increase of components. However, the lower capacitance bridge diode is in series with the much higher capacitance of the TVS diode, minimizing the added capacitance. The schematic shows tow bridge diodes in series to further reduce the line capacitance and increase the protection voltage by the additional VF value.

TVS diodes are also considered in secondary ESD protection schemes. It is important to determine the energy transfer across the windings so the a TVS diode can be suitably selected for the application. A TVS diode reference voltage will increase as current flow through it increases.

Here, a 3.3V TVS diode array solution using the ######## in a small DFN10 package is shown on a high-speed GigaBit Ethernet port.

New Ethernet power solutions such as Power over Ethernet (POE) and Power over Ethernet Plus (POEP) are being developed.

In summary, Leiditech ESD Protection products provide new, high-density integrated passive &active component technology with significant benefits such as cost-reduction and enhanced performance for any application.