CS61304A Cirrus Logic, Inc., CS61304A Datasheet - Page 29

• Manufacturer Part Number: CS61304A
• Description: T1-E1 Line Interface Unit for CPE-ISDN PRI
• Manufacturer: Cirrus Logic, Inc.

The receiver transformer has a grounded center
tap on the IC side. Resistors between the RTIP
and RRING pins to ground provide the termina-
tion for the receive line.
The transmitter transformer matches the 75
transmitter output impedance to the line imped-
ance. Figures A1-A3 show a 0.47 F capacitor in
series with the transmit transformer primary. This
capacitor is needed to prevent any output stage
imbalance from resulting in a DC current through
the transformer primary. This current might satu-
rate the transformer producing an output offset
level shift.
Transformers
Recommended transmitter and receiver trans-
former specifications are shown in Table A2. The
transformers in Table A3 are recommended for
use with the CS61304A. Refer to the "Telecom
Transformer Selection Guide" for detailed sche-
matics which show how to connect the line
interface IC with a particular transformer.
Selecting an Oscillator Crystal
Specific crystal parameters are required for
proper operation of the jitter attenuator. It is rec-
ommended that the Crystal Semiconductor
DS156PP2
Secondary Leakage Inductance
Primary Leakage Inductance
Interwinding Capacitance
Primary Inductance
Turns Ratio
ET-constant
Parameter
Table A2. Transformer Specifications
600 H min. @ 772 kHz
1.3 H max. @ 772 kHz
0.4 H max. @ 772 kHz
16 V- s min. for T1
12 V- s min. for E1
1:2 CT 5%
23 pF max.
Receiver
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
CS61304A in local loopback mode can be used
as a jitter attenuator. The inputs to the jitter at-
tenuator 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 "Telecom Line Protection
Application Note" for detailed information on the
different electrical safety standards and specific
application circuit recommendations.
1:1.26 1.5 % for 120
1:1.15 5 % for 100
1.5 mH min. @ 772 kHz
0.3 H max. @ 772 kHz
0.4 H max. @ 772 kHz
1:1 1.5 % for 75
16 V- s min. for T1
12 V- s min. for E1
Transmitter
18 pF max.
CS61304A
E1
T1
E1
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