LE87220KQC Zarlink, LE87220KQC Datasheet - Page 12

• Manufacturer Part Number: LE87220KQC
• Description: World Wide xDSL Line Driver 24-Pin QFN Tray
• Manufacturer: Zarlink

Specifications of LE87220KQC

• Package: 24QFN
• Transmission Media Type: Copper
• Power Supply Type: Analog
• Typical Operating Supply Voltage: 3.3 V
• Minimum Operating Supply Voltage: 3.13 V
• Maximum Operating Supply Voltage: 3.46 V

RECEIVER AND HYBRID CIRCUIT
The receive and hybrid circuit architecture depends greatly on the data AFE being used in the design. Some data AFEs have
built-in input differential amplifiers for the receive circuits. These amplifiers should be used to implement the receive and hybrid
functions. If the AFE does not have such amplifiers, then external low noise amplifiers are required to implement these functions.
Figure 4 shows a typical implementation of the receive and hybrid functions.
COMPONENTS SELECTION
The DC blocking capacitor C
TIP (A) and RING (B) terminals. The value of the line side capacitor depends on transformer primary inductance chosen to give
desired –3 dB high pass point. According to T1.413, the impedance measured across TIP (A) and RING (B) at 4 kHz must be
greater than 1100 Ω, which requires a capacitance of less than 35 nF for the series combination of C
blocking capacitor.
The minimum transformer primary inductance required is dictated by the low end of the upstream frequency band, which is
typically around 25-30 kHz. Since the transformer primary inductance shunts the line, it should be relatively high to avoid signal
attenuation and maintain an acceptable match across the desired bandwidth. A high impedance can be obtained by using a
transformer with a high primary side inductance while maintaining relatively low DC resistance for minimum insertion loss.
Besides using it for its isolation and high common-mode rejection it is also used as part of the high-pass splitter function.
If the -3 dB point is chosen to be around 20 kHz, the minimum primary (line side) inductance required would be
For the Le87220 device, a transformer primary side inductance of >800 µH is recommended
DATA AFE
6
is required on the primary or line side of the transformer in order to avoid applying a DC short across
UPP
UPN
L
PRI
RECEIVER AND HYBRID CIRCUIT
Figure 4. Receive and Hybrid Circuit
=
----------------------------- -
2π 20 kHz
+
+
-
-
Z
(
LOOP
Zarlink Semiconductor Inc.
AGND
)
=
----------------------------- -
2π 20 kHz
C
C
12
12
13
(
100
R
R
R
R
6
7
8
9
)
≈
796 µH
R
R
4
C
5
C
10
11
.
REC+
HYB+
HYB-
REC-
6
and any external DC