2795N

HIGH FREQUENCY MAGNETICS Application Note for Miniature Pulse Transformer 2795N Transformer Application Note The 2795N transformer provides two transformation ratios to match both 120Ω and 75Ω line impedances with Lucent 5 V transceivers. The ratio of the two transformer impedance ratios is within 0.07% of the ratio of the two line impedances. This virtually perfect match allows the transformer to work with a single terminating network design for both line impedances. The transformer can also be used for 100Ω lines with a change in resistor values. For 2795N data sheet refer to document TM9918. TM9919A Suggested External Line Termination Network for Lucent 5 V Line Transceivers A suggested line termination network consisting of the 2795N transformer, a capacitor, and resistors arranged to provide the proper voltage gain and impedance matching to the characteristic impedance of the transmission line is shown below. The diagram shows the appropriate external components for a receive line interface and a transmit line interface for one channel. The network is designed to operate with both E1 cable impedances (75Ω and 120Ω) with no change in components. For DS1 applications (100Ω), only the resistor values need to be changed. The same transformer can be used for all three cable impedances in both receive and transmit operation. Figure 1 below shows the proper connections for each cable impedance. The components and values are listed in Table 1 (see next page). 2795N Transformer Receive Data 4 3 RR RTIP CC ZO (Line) 75 2 5 1 120 100 T1 6 RS RR RRING Device (1 Channel) 2795N Transformer Transmit Data 3 4 RT TTIP 2 ZO (Line) 6 T2 5 1 75 120 100 RT TRING Figure 1. Connections for each cable impedance ©1999 Bel Fuse Inc. Specifications subject to change without notice. 06.99 Bel Fuse Inc. 198 Van Vorst Street, Jersey City, NJ 07302 • Tel 201-432-0463 • Fax 201-432-9542 • www.belfuse.com T136 HIGH FREQUENCY MAGNETICS TM9919A Application Note for Miniature Pulse Transformer 2795N Transformer Application Note Symbol ZO CC RR RS RT T1, T2 Name Characteristic impedance Center tap capacitor Receive series resistor Receive shunt resistor Transmit series resistor Bel part number Value 75Ω (E1) 0.1 µF 36.5Ω 64.9Ω 25.5Ω 2795N 120Ω (E1) 0.1 µF 36.5Ω 64.9Ω 25.5Ω 2795N 100Ω (DS1) 0.1 µF 30.1Ω 53.6Ω 4.6Ω 2795N Table 1. Line termination components and values ©1999 Bel Fuse Inc. Specifications subject to change without notice. 06.99 CORPORATE Bel Fuse Inc. 198 Van Vorst Street Jersey City, NJ 07302 Tel 201-432-0463 Fax 201-432-9542 www.belfuse.com FAR EAST Bel Fuse Ltd. 8F / 8 Luk Hop Street San Po Kong Kowloon, Hong Kong Tel 852-2328-5515 Fax 852-2352-3706 www.belfuse.com EUROPE Bel Fuse Europe Ltd. Preston Technology Management Centre Marsh Lane, Suite F23, Preston Lancashire, PR1 8UD, U.K. Tel 44-1772-556601 Fax 44-1772-888366 www.belfuse.com T137