BOURNS ® TCS ™ TRANSIENT CURRENT SUPPRESSOR WHITE PAPER A New Circuit Protection Device for VDSL Applications INTRODUCTION Bourns® TCS™ Devices Since the first electronic equipment was designed, engineers have had to deal with protecting their equipment against electrical surges, primarily Electrostatic Discharge (ESD) and lightning. Equipment interfaces can be exposed to a wide range of discharge events up to and including surges caused by lightning. Even with ESD-immune optical fibers transmitting data long distances, connection from the optical-electrical interface equipment to offices and residential buildings is still primarily through external conventional electrical cabling, exposing this equipment to high energy electrical surges. Modern electronics, in the quest for ever higher speed and lower cost, use ever denser IC technologies whose sensitivity to surges creates an increasingly difficult challenge for designers of electronic equipment. As technology advances, conventional circuit protection solutions have become less effective in protecting sensitive electronics from surges. Furthermore, these conventional solutions struggle to meet the signal integrity requirements for very high-speed transmissions. This white paper examines how the new Bourns® Transient Current Suppressor (TCS™) protection device can meet the surge protection and transmission performance challenges of modern communication systems.

BOURNS ® TCS ™ TRANSIENT CURRENT SUPPRESSOR WHITE PAPER A New Circuit Protection Device for VDSL Applications LIMITATIONS OF THE TRANSIENT VOLTAGE SUPPRESSOR Basic Operation of a Voltage Limiting Device Bourns® TCS™ Devices Electronic protection devices have been developed to absorb ESD energy at the interface, and one of the most commonly used devices is a Transient Voltage Suppressor (TVS) diode. The basic operation of a TVS diode is very simple (see figure 1). Ideally, it has an electrical characteristic as shown in figure 2, whereby the device appears as high impedance to the interface in...

BOURNS ® TCS ™ TRANSIENT CURRENT SUPPRESSOR WHITE PAPER A New Circuit Protection Device for VDSL Applications LIMITATIONS OF THE TRANSIENT VOLTAGE SUPPRESSOR (Continued) 12 IDEAL CLAMP ACTUAL TVS DIODE (CDSOT23-SRV05-4) Bourns® TCS™ Devices PEAK SURGE CURRENT (A) Comparison between an Ideal 5 V TVS Diode Characteristic (Black Line) and an Actual TVS Diode (Model CDSOT23-SRV05-4) (Red Line) In practice, a TVS diode appears high resistance until the breakdown voltage of the junction is reached. Beyond that point, the diode junction supports current flow in the form of avalanche, Zener or punch-through...

BOURNS ® TCS ™ TRANSIENT CURRENT SUPPRESSOR WHITE PAPER A New Circuit Protection Device for VDSL Applications LIMITATIONS OF THE TRANSIENT VOLTAGE SUPPRESSOR (Continued) Surge Event with Typical Ideal TVS Diode Bourns® TCS™ Devices Protected Device Let-through Energy Surge Surge Absorbed Energy The Protected Device Experiences the Same High Voltage Transient as the TVS Diode The potentially high level of let-through energy under surge conditions can be a major problem when using conventional TVS diodes for the protection of sensitive electronics in harsh environments.

BOURNS ® TCS ™ TRANSIENT CURRENT SUPPRESSOR WHITE PAPER A New Circuit Protection Device for VDSL Applications IMPACT OF TVS CAPACITANCE ON SIGNAL INTEGRITY Bourns® TCS™ Devices As data rates and transmission distances increase, a further consideration is the high frequency characteristics of the surge protection device during normal line use. High capacitance can cause unacceptable high frequency attenuation in the circuit, significantly limiting the capacity to drive high data rates. Junction capacitance is non-linear, and the dynamic capacitance variation with signal voltage can result in unacceptable...

BOURNS ® TCS ™ TRANSIENT CURRENT SUPPRESSOR WHITE PAPER A New Circuit Protection Device for VDSL Applications BOURNS® TCS™ TRANSIENT CURRENT SUPPRESSOR: A NEW APPROACH Bourns® TCS™ Devices The Transient Current Suppressor (TCS™) device is a new approach that significantly improves the level of protection when used in a two-stage configuration together with a voltage limiting device, in series with the protected signal line. The actual characteristics of the TCS™ device are shown in detail in figure 4. Normalized Current The problems inherent in achieving ideal TVS characteristics, in combination...

BOURNS ® TCS ™ TRANSIENT CURRENT SUPPRESSOR WHITE PAPER A New Circuit Protection Device for VDSL Applications BOURNS® TCS™ TRANSIENT CURRENT SUPPRESSOR: A NEW APPROACH (Continued) The TCS™ device configuration and circuit symbol are shown in figure 5. Bourns TCS Devices ® Normal Operation Protected Device Signal Bourns® TCS™ High-Speed Protector Very low resistance and insertion loss of TCS™ device barely affects the signal. Low capacitance, low cost diode clamp can be used, minimizing signal degradation. Surge Event with TCS™ Device Protected Device Very Low Let-through Energy Surge Surge Bourns®...

BOURNS ® TCS ™ TRANSIENT CURRENT SUPPRESSOR WHITE PAPER A New Circuit Protection Device for VDSL Applications BOURNS® TCS™ TRANSIENT CURRENT SUPPRESSOR: A NEW APPROACH (Continued) Bourns® TCS™ Devices When used in conjunction with a TCS™ device, the first stage clamp voltage level no longer needs to be critically chosen to match the protected device and its clamping characteristic may be much softer (resistive) than a single stage TVS diode would need to be. The voltage across the clamp voltage device can continue to rise, with the maximum limitation now being that the differential voltage developed...

BOURNS ® TCS ™ TRANSIENT CURRENT SUPPRESSOR WHITE PAPER A New Circuit Protection Device for VDSL Applications BOURNS® TCS™ TRANSIENT CURRENT SUPPRESSOR: A NEW APPROACH (Continued) Bourns® TCS™ Devices Several device options of resistance and current limit are available, and can be chosen for optimal cost and performance in the application: TCS™ Device Options Typical Current Limit (mA) The TCS™ device acts like a conventional linear low value resistor in series with the line, so there is no physical connection to ground for internal parasitic capacitance to occur. As with a resistor, the only...