PROTECTION SOLUTIONS

Protection Must Fit the Application

Two factors are important in choosing circuit protection components; understanding what the equipment needs to be protected against, and ensuring that the protection itself does not impair the normal operation of the system. The most common solutions are small silicon-based zener or TVS (Transient Voltage Suppressor) diodes or MultiLayer Varistors (MLVs) such as those available from Bourns.



There are several ways of assessing the risk to equipment from ElectroStatic Damage (ESD). ICs are typically rated to 1kV or 2kV contact voltage to protect them against damage during assembly. IEC 61000-4.2 specifies Human Body Models (HBMs) up to 8kV, although there are suggestions that this may be increased since HBMs can reach 25kV in static-rich environments.

The ESD protector has a reaction time associated with it when tested under the high dV/dT (8kV/ns) conditions that govern the overshoot of the protector. It is therefore important to ensure that the IC or circuit being protected can support this peak voltage.

For high data-rate lines, the capacitance of the protector may become an issue. The Bourns ChipGuard CG0603MLC-xxLE air-gap varistor and CDSOD323-T05C TVS Diode were designed to provide ultra-low capacitance of 0.5pF and 3pF, respectively while having almost negligible leakage current. These devices have negligible effect on signal quality at 480Mbit/s, and can be considered in applications at 1Gbit/s and beyond. For applications below 480Mbit/s, designers can consider the cost-effective CDDFN4-T05 device with a higher maximum capacitance of 10pF.

Although power supplies are generally immune to ESD conditions, ferrite beads are commonly used to add additional series inductance to limit the impulse amplitudes under fast transients. Overvoltage protection solutions that can support higher energy densities, such as the Bourns CDDFN2-T4.7C or CDSOD323-T05C, can be considered to reduce the strain on other components.

Bourns’ solutions for USB interconnections include the MF-NSMF150-2 surface mount resettable fuse to prevent damage on the USB Vbus line. USB 1.1 data lines may be protected with the CD143A-SR05, while higher data rate USB 2.0 connections require use of the CDSOD323-T05C or CG0603MLC-05LE devices. The CDSOT23-SR208 steering diode array, capable of protecting four lines in a single package, is the solution of choice for space-constrained applications such as USB OTG.

Features

• Range of circuit protection components
• TVS diodes
• Resettable fuses
• Varistors
• Low capacitance options: down to 0.5pF
• Cost-effective options for lower data rates: 10pF
• Integrated chip-type solutions protecting multiple lines
• IEC 61000-4.2 compliant

Applications

• Portable electronics
• Mobile telephones
• Video and graphics cards
• Sensors
• USB interfaces
• Ethernet interfaces

For further information, including the Bourns Shortform Catalogue, please click here