2795T Datasheet, PDF (1/4 Pages) Bel Fuse Inc. – HIGH FREQUENCY MAGNETICS Application Note for Miniature Pulse Transformers

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 [phone] • Fax [phone] • www.belfuse.com
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