Sidactor Protection Thyristor Products Page 43 SIDACtor Protection Thyristor Products

SIDACtor Protection Thyristors 2017 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 02/23/17 TIA-968-A applies to all terminal equipment connected to the Public Switched Telephone Network (PSTN) in the USA, and holds the "rule of law" by congressional order. The purpose of TIA-968-A is to provide a set of uniform standards to protect the telephone network from any damage or interference caused by the connection of terminal equipment. This standard includes environmental simulations such as vibration tests, temperature and humidity cycling, drop tests and tests for hazardous voltages and currents, as well as tests for signal power levels, line balance, on-hook impedance, and billing protection. All these standards must be met before and after the environmental tests are applied. TIA-968-A compliant equipment must undergo an overvoltage test that includes a Type A and Type B Metallic Voltage Surge and a Type A and Type B Longitudinal Voltage Surge. These surges are part of the environmental simulation, and although a provision does allow the EUT to reach an open circuit failure mode during the Type A tests, failures must: 1. Arise from an intentional design that will cause the phone to be either disconnected from the public network or repaired rapidly 2. Be designed so that it is substantially apparent to the end user that the terminal equipment is not operable [A common example of an acceptable failure would be an open circuit due to an open connection on either Tip or Ring.] For Type B surges, equipment protection circuitry is not allowed to fail. The EUT must be designed to withstand Type B surges and continue to function in all operational states. Overvoltage Test The Type A and Type B Metallic Voltage Surges are applied in both the positive and negative polarity across Tip and Ring during all operational states (on-hook, off-hook, ringing, and so on). The Type A surge is an 800 V, 100 A peak surge while the Type B surge is a 1000 V, 25 A peak surge, as presented in Table 3.29. Metallic Voltage Surge Table 3.29 TIA-968-A Voltage Surge Surge Type Peak Voltage (V PK ) Rise & Decay Time (Voltage Waveform) Peak Current (A) Rise & Decay Time (Current Waveform) Repetitions Each Polarity Metallic A 800 10x560 s 100 10x560 s 1 Longitudinal A 1500 10x160 s 200 10x160 s 1 Metallic B 1000 9x720 s 25 5x320 s 1 Longitudinal B 1500 9x720 s 37.5 5x320 s 1 Notes: For Type A surges, the EUT may pass either "operationally" or "non-operationally." For Type B surges, the EUT must pass "operationally." The peak current for the Type A longitudinal surge is the total available current from the surge generator. The peak current for the Type B longitudinal surge is the current supplied to each conductor. Longitudinal Voltage Surge The Type A and Type B Longitudinal Voltage Surges are applied in both positive and negative polarity during all operational states. The Type A surge is a 1500 V, 200 A peak surge applied to the EUT with Tip and Ring tied together with respect to Ground. The Type B Longitudinal Voltage Surge is a simultaneous surge in which 1500 V and 37.5 A are applied concurrently to Tip with respect to Ground and Ring with respect to Ground, as presented in Table 3.29. Note : Type B surge requirements guarantee only a minimum level of surge protection. For long term reliability of terminal equipment, consideration should be given to complying with Type A surges operationally. Another important aspect of TIA-968-A is on-hook impedance, which is affected by transient protection. On-hook impedance is analogous to the leakage current between Tip and Ring, and Tip, Ring, and Ground conductors during various on-hook conditions. "On-hook Impedance Measurements" (next paragraph) outlines criteria for on-hook impedance and is listed as part of the Ringer Equivalent Number (REN). The REN is the largest of the unitless quotients not greater than five; the rating is specified as the actual quotient followed by the letter of the ringer classification (for example, 2B). On-hook Impedance Limitations On-hook impedance measurements are made between Tip and Ring and between Tip and Ground and Ring and Ground. For all DC voltages up to and including 100 V, the DC resistance measured must be greater than 5 M. For all DC voltages between 100 V and 200 V, the DC resistance must be greater than 30 k. The REN values are then determined by dividing 25 M by the minimum measured resistance up to 100 V and by dividing 150 k by the minimum measured resistance between 100V and 200V. On-hook impedance is also measured during the application of a simulated ringing signal. This consists of a 40 V rms through 150 V rms ringer signal at frequencies ranging from 15.3 Hz to 68 Hz superimposed on a 56.5 V dc for a class "B" ringer. During this test, the total DC current may not exceed 3 mA. In addition, the minimum DC resistance measured between Tip and Ring must be greater than 1600, while the DC resistance measured between the Tip and Ring conductors and Ground must be greater than 100 k. The REN values for the simulated ringing test are determined by dividing the maximum DC current flowing between Tip and Ring by 0.6 mA, and by dividing 8000 by the minimum impedance value measured. On-hook Impedance Measurements Regulatory Requirements (continued) TIA-968-A (formerly known as FCC Part 68)

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