Sidactor Protection Thyristor Products Page 11 SIDACtor Protection Thyristor Products

SIDACtor Protection Thyristors 2017 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 02/23/17 Selection Criteria When selecting a SIDACtor device, use the following criteria: Off-state Voltage (V DRM ) The V DRM of the SIDACtor device must be greater than the maximum operating voltage of the circuit that the SIDACtor device is protecting. Example 1: For a POTS (Plain Old Telephone Service) application, convert the maximum operating Ring voltage (150 V RMS ) to a peak voltage, and add the maximum DC bias of the central office battery: 150 V RMS 2 + 56.6 V PK = 268.8 V PK 4 V DRM > 268.8 V Example 2: For an ISDN application, add the maximum voltage of the DC power supply to the maximum voltage of the transmission signal (for U.S. applications, the U-interface will not have a DC voltage, but European and Japanese ISDN applications may): 150 V PK + 3 V PK = 153 V PK f V DRM > 153 V Switching Voltage (V S ) The V S of the SIDACtor device should be equal to or less than the instantaneous peak voltage rating of the component it is protecting. Example 1: V S V Relay Breakdown Example 2: V S SLIC V PK Peak Pulse Current (I PP ) For circuits that do not require additional series resistance, the surge current rating (I PP ) of the SIDACtor device should be greater than or equal to the surge currents associated with the lightning immunity tests of the applicable regulatory requirement (I PK ): I PP I PK For circuits that use additional series resistance, the surge current rating (I PP ) of the SIDACtor device should be greater than or equal to the available surge currents associated with the lightning immunity tests of the applicable regulatory requirement (I PK(available) ): I PP I PK(available) The maximum available surge current is calculated by dividing the peak surge voltage (V PK ) by the total circuit resistance (R TOTAL ): I PK(available) = V PK /R TOTAL For longitudinal surges (Tip-Ground, Ring-Ground), R TOTAL is calculated for both Tip and Ring: R SOURCE = V PK /I PK R TOTAL = R TIP + R SOURCE R TOTAL = R RING + R SOURCE For metallic surges (Tip-Ring): R SOURCE = V PK /I PK R TOTAL = R TIP + R RING + R SOURCE Example 1 : A modem manufacturer must pass the Type A surge requirement of TIA-968-A without any series resistance. I PK = 100 A, 10x560 s I PP 100 A, 10x560 s Therefore, either a "B" rated or "C" rated SIDACto r device would be selected. Example 2: A line card manufacturer must pass the surge requirements of GR 1089 with 30 on Tip and 30 on Ring. I PK = 100 A, 10x1000 s V PK = 1000 V R SOURCE = V PK /I PK = 10 R TOTAL = R SOURCE + R TIP = 40 I PK (available) = V PK /R TOTAL = 1000 V/40 4 I PP 25 A Off-State Capacitance (C O ) Assuming that the critical point of insertion loss is 70 percent of the original signal value, the SIDACtor device can be used in most applications with transmission speeds up to 30 MHz. For transmission speeds greater than 30 MHz, the new MC series is highly recommended. Holding Current (I H ) Because TIA-968-A 4.4.1.7.3 specifies that registered terminal equipment not exceed 140 mA dc per conductor under short-circuit conditions, the holding current of the SIDACtor device is set at 150 mA. For specific design criteria, the holding current (I H ) of the SIDACtor device must be greater than the DC current that can be supplied during an operational and short circuit condition.

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