Surge Arrestors Offer Ultra Low Capacitance for xDSL Applications

Fully compatible with digital transmission standards such as ADSL2 and ADSL2+, the SMP80MC family of micro-capacitance transient surge arrestors is the first series for which the junction capacitance does not depend on the device breakdown voltage. This is first family of devices to combine an 80A repetitive peak pulse current rating with a low capacitance of only 12pF, typical.

Telecommunications systems are particularly vulnerable to lightning-induced surges and two levels of protection are normally required: a primary suppressor on each line to absorb the major part of the overvoltage transient and secondary protection devices mounted on individual PCBs to eliminate the residual overvoltage spikes. The primary suppressors must have high surge current capabilities and be able to withstand very high voltages. ST’s TRISIL technology offers superior performance, including a long service life without ageing, tight voltage tolerance, fast response times and failsafe operation, compared to non-silicon alternatives, such as gas discharge tubes. Moreover, the failure mode in the event of an extreme lightning surge results in a short circuit that protects both equipment and personnel.

Compliant with major standards such as GR-1089 Core, ITU-T-K20/K21, VDE0433, VDE0878, IEC61000-4-5 and FCC part 68, the expanded family provides fast, bidirectional crowbar protection with maximum surge currents up to 80A (10/1000µs). By optimising the trade-off between repetitive peak pulse current and capacitance for broadband transmission, ST has engineered devices having a surge capability of 80A (10/1000µs) and a capacitance of 12pF at 50V.

Key parameters of the devices include voltage range from 120V to 270V, a maximum leakage current of only 2µA, a maximum breakover voltage up to 345V and a minimum holding current of 150mA. The devices are housed in surface-mount SMB packages (JEDEC DO-214AA).

Ideal for protecting telephone, fax, modem and similar sensitive equipment against lightning strikes and power crossing events, the SMP80MC devices are in full production and cost $0.18 in quantities of 2500 pieces.