MC145572AE Freescale Semiconductor, MC145572AE Datasheet - Page 221

• Manufacturer Part Number: MC145572AE
• Manufacturer: Freescale Semiconductor

Specifications of MC145572AE

• Number Of Line Interfaces: 1
• Control Interface: HDLC
• Lead Free Status / Rohs Status: Compliant

MOTOROLA
E.1
E.2
INTRODUCTION
The intent of this appendix is to provide information about the MC145572 2B1Q interface circuit
(excluding protection, dc termination, etc.) to compute optimal component values for line interface
and transformer solutions. It also provides some basic explanation regarding the function of each of
the components in the 2B1Q interface circuit.
CALCULATION OF TRANSMIT SERIES RESISTORS
The transmit series resistor values, R x , depend on the amount of dc winding resistance of the trans-
former. The values of these resistors also depend on the impedance of the 1 F dc blocking capacitor,
C b . Any resistors added to the line side of the transformer for primary circuit protection may be added
to the dc winding resistance of the line side windings of the transformer. Portions of the line interface
circuit are internal to the MC145572. The entire line interface circuit model is shown in Figure E–1.
The total transmit circuit model is shown in Figure E–2. Due to the duplexer nature of the line interface
circuit, R x P and R x N are at virtual signal ground for transmitted signals. Thus, each R f appears in
parallel with each R g (see Figure E–2), but since R g is so low, R f can be ignored. The output imped-
ance of the transmit drivers has been included in this model, but will be subsequently ignored due
to its insignificant nature.
The transmit model is simplified to include the reflected impedances from the line side of the trans-
former. The output impedances of the transmit drivers are omitted here. This is shown in Figure E–3.
Tx DRIVER
LINE INTERFACE CIRCUIT COMPONENT
Freescale Semiconductor, Inc.
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Figure E–1. Line Interface Circuit Model
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R f
R f
MC145572
R i
R i
VALUE CALCULATIONS
R x P
R x N
T x N
T x P
R x
R x
C1
1:N
C b
R TP
R TP
R L
E
E–1