2795T

HIGH FREQUENCY MAGNETICS Application Note for Miniature Pulse Transformers TM00145B 2795T and 2795Y Transformers Application Note The 2795T and 2795Y transformers provide two transformation ratios to match both 75Ω and 120Ω line impedances with Lucent 3.3 V transceivers using a single terminating network design. These dual-ratio transformers can also be used for 100Ω lines with a change in resistor values. The 2795T is optimized for the receive function, while the 2795Y is optimized for the transmit function. The 2795T can be used for both receive and transmit operation; the 2795Y is designed for transmit operation only. Suggested applications for a single-transformer design solution (two 2795T transformers) are shown in Figure 1. The recommended two-transformer design solution (2795T and 2795Y) is shown in Figure 2. For 2795T and 2795Y data sheet refer to document TM00145. Single-Transformer Design and Common Termination Network A typical line termination network using the 2795T transformer for both the receive interface and the transmit interface is shown below for a single channel. The termination network consists of capacitors and resistors arranged to provide the proper voltage gain and impedance matching to the characteristic impedance of the various transmission lines. 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. Connections for cable selection are made on the line side for the receive interface and on the device side for the transmit interface. The components and suggested values are listed in Table 1. Capacitor CS provides high-frequency return loss enhancement. ©2000 Bel Fuse Inc. Specifications subject to change without notice. 07.00 Bel Fuse Inc. 198 Van Vorst Street, Jersey City, NJ 07302 • Tel 201-432-0463 • Fax 201-432-9542 • www.belfuse.com T1-103 HIGH FREQUENCY MAGNETICS TM00145B Application Note for Miniature Pulse Transformers 2795T and 2795Y Transformers Application Note 2795T Transformer 4 3 Receive Data RR RTIP CC ZO (Line) 75 120 100 Transmit Data 2 5 1 T1 2795T Transformer 3 4 6 RS RR RRING Device (1 Channel) RT TTIP CS RT 2 ZO (Line) 6 T2 120 100 5 1 75 TRING Figure 1. Connections for two 2795T transformers Symbol Zo CC RR RS RT CS T1 T2 Name Characteristic impedance Center tap capacitor Receive series resistor Receive shunt resistor Transmit series resistor Shunt capacitor Bel part number—receive Bel part number—transmit Value 75Ω (E1) 120Ω (E1) 0.1 µF 0.1 µF 158Ω 158Ω 114Ω 114Ω 6.2Ω 6.2Ω 470 pF 470 pF 2795T 2795T 2795T 2795T 100Ω (DS1) 0.1 µF 132Ω 95.3Ω 1.2Ω 470 pF 2795T 2795T Table 1. Components and values for two 2795T transformers ©2000 Bel Fuse Inc. Specifications subject to change without notice. 07.00 Bel Fuse Inc. 198 Van Vorst Street, Jersey City, NJ 07302 • Tel 201-432-0463 • Fax 201-432-9542 • www.belfuse.com T1-104 HIGH FREQUENCY MAGNETICS Application Note for Miniature Pulse Transformers TM00145B 2795T and 2795Y Transformers Application Note Two-Transformer Design and Common Termination Network A typical line termination network using the 2795T transformer for the receive interface and the 2795Y transformer for the transmit interface is shown below for a single channel. The termination network consists of capacitors and resistors arranged to provide the proper voltage gain and impedance matching to the characteristic impedance of the various transmission lines. 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 2795T transformer is used for all three cable impedances at the receive interface. The 2795Y transformer is used for all three cable impedances at the transmit interface. Figure 2 below shows the proper connections for each cable impedance. Connections for cable selection are made on the line side for both receive and transmit interfaces. The components and suggested values are listed in Table 2. Capacitor CS provides high-frequency return loss enhancement. Receive Data 2795T Transformer 4 3 RR RTIP CC ZO (Line) 75 120 100 Transmit Data 2 5 1 T1 2795Y Transformer 4 2 6 RS RR RRING Device (1 Channel) 3 RT TTIP ZO (Line) 75 120 100 CS 5 1 T2 6 RT TRING Figure 2. Connections for one 2795T transformer and one 2795Y transformer ©2000 Bel Fuse Inc. Specifications subject to change without notice. 07.00 Bel Fuse Inc. 198 Van Vorst Street, Jersey City, NJ 07302 • Tel 201-432-0463 • Fax 201-432-9542 • www.belfuse.com T1-105 HIGH FREQUENCY MAGNETICS TM00145B Application Note for Miniature Pulse Transformers 2795T and 2795Y Transformers Application Note Symbol Zo CC RR RS RT CS T1 T2 Name Characteristic impedance Center tap capacitor Receive series resistor Receive shunt resistor Transmit series resistor Shunt capacitor Bel part number—receive Bel part number—transmit Value 75Ω (E1) 120Ω (E1) 0.1 µF 0.1 µF 158Ω 158Ω 114Ω 114Ω 7.15Ω 7.15Ω 330 pF 330 pF 2795T 2795T 2795Y 2795Y 100Ω (DS1) 0.1 µF 132Ω 95.3Ω 1.8Ω 330 pF 2795T 2795Y Table 2. Components and values for one 2795T transformer and one 2795Y transformer ©2000 Bel Fuse Inc. Specifications subject to change without notice. 07.00 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 G7, Preston Lancashire, PR1 8UD, U.K. Tel 44-1772-556601 Fax 44-1772-888366 www.belfuse.com T1-106