Transformers
Recommended transmitter and receiver trans-
former specifications are shown in Table A2. The
transformers in Table A3 have been tested and
recommended for use with the CS61574A and
CS61575. Refer to the "Telecom Transformer Se-
lection Guide" for detailed schematics which
show how to connect the line interface IC with a
particular transformer.
In applications where it is advantageous to use a
single transmitter transformer for 75Ω and 120Ω
E1 applications, a 1:1.26 transformer may be
used. Although transmitter return loss will be re-
duced for 75Ω applications, the pulse amplitude
will be correct across a 75Ω load.
Selecting an Oscillator Crystal
Specific crystal parameters are required for
proper operation of the jitter attenuator. It is rec-
ommended that the Crystal Semiconductor
CXT6176 crystal be used for T1 applications and
the CXT8192 crystal be used for E1 applications.
Designing for AT&T 62411
For additional information on the requirements of
AT&T 62411 and the design of an appropriate
system synchronizer, please refer to the Crystal
Semiconductor Application Notes: "AT&T 62411
Design Considerations – Jitter and Synchroniza-
tion" and "Jitter Testing Procedures for
Compliance with AT&T 62411".
Transmit Side Jitter Attenuation
In some applications it is desirable to attenuate
jitter from the signal to be transmitted. A
CS61575 in local loopback mode can be used as a
jitter attenuator. The inputs to the jitter attenuator
are TPOS, TNEG, TCLK. The outputs from the
jitter attenuator are RPOS, RNEG and RCLK.
Line Protection
Secondary protection components can be added
to provide lightning surge and AC power-cross
immunity. Refer to the application note "Secon-
dary Line Protection for T1 and E1 Line Cards"
for detailed information on the different electrical
safety standards and specific application circuit
recommendations.
Parameter Receiver Transmitter
Turns Ratio
1:2 CT ± 5% 1:1 ± 1.5 % for 75 Ω E1
1:1.15 ± 5 % for 100 Ω T1
1:1.26 ± 1.5 % for 120 Ω E1
Primary Inductance
600 μH min. @ 772 kHz
1.5 mH min. @ 772 kHz
Primary Leakage Inductance
1.3 μH max. @ 772 kHz 0.3 μH max. @ 772 kHz
Secondary Leakage Inductance
0.4 μH max. @ 772 kHz 0.4 μH max. @ 772 kHz
Interwinding Capacitance 23 pF max. 18 pF max.
ET-constant
16 V-μs min. for T1
12 V-μs min. for E1
16 V-μs min. for T1
12 V-μs min. for E1
Table A2. Transformer Specifications
CS61574A CS61575
30 DS154F3
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