cx28380 Mindspeed Technologies, cx28380 Datasheet - Page 32

• Manufacturer Part Number: cx28380
• Description: Cn8380 Quad T1/e1 Line Interface
• Manufacturer: Mindspeed Technologies

XTIP and XRING. The recommended value for Ct is 200 pF. If other components are also connected to XTIP/
XRING, such as surge protection diodes, Ct’s value should be adjusted to maintain a total parallel capacitance of
approximately 200 pF.
Rt is a parallel termination resistor selected to provide the required transmitter return loss, typically –18 dB. If an
application does not have a return loss requirement, Rt can be omitted in order to reduce total power consumption.
The standard transformer recommended has a turns ratio of 1:2. This turns ratio is required if parallel termination
(Rt) or series resistors (Rs) are desired. The alternate transformer has a turns ratio of 1:1.36. This transformer can
be used only if all of the following are true:
•
•
•
See Option E in
unterminated, standard transformer configuration.
Resistors (Rs) in series with Tx TIP and Tx RING line connections are sometimes used with surge protection
circuits. Without compensation, the addition of these resistors decreases the transmit pulse amplitude. The
CX28380 provides an option in Host Mode to boost the output level if resistors are installed. Compensation is
optimized for the use of 5.6 Ω Rs values. In Hardware Mode, these resistors are required.
Figure 2-8.
Tables 2-4
information for all termination options supported. The resulting return loss value is also listed. All five options are
supported in Host Mode, whereas only options C and D are supported in Hardware Mode.
Before selecting a termination option, see
Termination tables below to select a termination option.
2.4.6.1.1
Option A uses the standard 1:2 transformer, no series protection resistors (Rs), and no parallel termination (Rt) for
T1 applications. In E1 applications, Rt is included because it is usually required to provide a minimal level of line
impedance matching. Option A is applicable in Host Mode only.
29380-DSH-001-B
Parallel termination (Rt) is not used.
Series resistors (Rs) are not used.
T1 DSX-1 transmit pulse is not used.
through
Transmit Termination Components
Table
Option A
2-8
8380_012
2-8. Transmitter power consumption is reduced by approximately 30%, compared to the
provide recommended termination component values and CX28380 configuration
Preliminary Information / Mindspeed Proprietary and Confidential
CX28380
XRING
XTIP
Mindspeed Technologies
Table
Ct
2-3, to select an application mode. Then see the Transmit
Rt
Transformer
1:N
®
Rs
Rs
Tx RING
Tx TIP
Circuit Description
24