2795N Datasheet, PDF (1/2 Pages) Bel Fuse Inc. – HIGH FREQUENCY MAGNETICS Application Note for Miniature Pulse Transformer

HIGH FREQUENCY MAGNETICS
Application Note for Miniature Pulse Transformer
TM9919A
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.
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).
Receive Data
2795N
Transformer
4
3
RR
RTIP
ZO
(Line)
75
120
100
Transmit Data
2 _CC
RS
5
1
6
RR
T1
2795N
Transformer
3
4
RT
RRING
Device
(1 Channel)
TTIP
ZO
(Line)
2
5 ¹²⁰
100 _RT
6
1
T2
75
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 [phone] • Fax [phone] • www.belfuse.com
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