MC145572AC Freescale Semiconductor, MC145572AC Datasheet - Page 223

• Manufacturer Part Number: MC145572AC
• Manufacturer: Freescale Semiconductor

Specifications of MC145572AC

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

MOTOROLA
E.3
The equation for calculating R x can be reduced to:
Substituting in values gives:
R x = 5000 *(135 – 7.9 *1.25 2 – 8.2 – 2 *5) / (8.2 + 7.9 *1.25 2 + 2 *5000 *1.25 2 + 2 *5 – 135)
CALCULATION OF TRANSMIT NOISE FILTER CAPACITOR
Once the transmit series resistor values have been calculated, the transmit noise filter capacitor can
be calculated for a 160 kHz cutoff frequency. This capacitor in conjunction with the transmit series
resistors acts as a low pass filter to remove the high frequency switching noise in the output signal
of the MC145572 TxP and TxN pins.
The nearest commercial value can be used.
The analysis yields the following line interface circuit (see Figure E–4).
= 33.65
= 33.7
R x = R i * (R L – N 2 * R p – 2 * R TP – R s ) / (R s + N 2 * R p + 2 * N 2 * R i + 2 * R TP – R L )
Freescale Semiconductor, Inc.
MC145572
For More Information On This Product,
RxN
RxP
TxN
TxP
Figure E–4. Calculated Line Interface Circuit
Go to: www.freescale.com
C1 = 1 / [2 * (2 * PI * 160000 * 33.7)]
MC145572
C1 = 1 / [2 * (2 * PI * f * R x )]
33.7
33.7
C1 = 0.015 F
0.015
F
1
F
5
5
T
N
R
E–3
(3)
(4)