Datasheet

+ +
N1 N2
Phase
Neutral
Low-Voltage
Capacitor
High-Voltage
Capacitor
Power
Amplifier
MOV
TVS
PA
Power Supply
D2
D1
D3
AFE031
+ +
N1 N2
Phase
Neutral
Low-Voltage
Capacitor
High-Voltage
Capacitor
L
Power
Amplifier
AFE031
www.ti.com SBOS531D –AUGUST 2010–REVISED MAY 2012
LINE-COUPLING CIRCUIT
The line-coupling circuit is one of the most critical circuits in a powerline modem. The line-coupling circuit has
two primary functions: first, to block the low-frequency signal of the mains (commonly 50 Hz or 60 Hz) from
damaging the low-voltage modem circuitry; second, to couple the modem signal to and from the ac mains. A
typical line-coupling circuit is shown in Figure 50.
Figure 50. Simplified Line Coupling Circuit
For additional information on line-coupling interfaces with the AFE031, refer to Application Report SBOA130,
Analog Front-End Design for a Narrowband Power-Line Communications Modem Using the AFE031 (available
for download at www.ti.com).
CIRCUIT PROTECTION
Powerline communications are often located in operating environments that are harsh for electrical components
connected to the ac line. Noise or surges from electrical anomalies such as lightning, capacitor bank switching,
inductive switching, or other grid fault conditions can damage high-performance integrated circuits if they are not
properly protected. The AFE031 can survive even the harshest conditions if several recommendations are
followed.
First, dissipate as much of the electrical disturbance before it reaches the AFE031 with a multi-layer approach
using metal-oxide varistors (MOVs), transient voltage suppression diodes (TVSs), Schottky diodes, and a Zener
diode. Figure 51 shows the recommended strategy for transient overvoltage protection.
Figure 51. Transient Overvoltage Protection for AFE031
Note that the high-voltage coupling capacitor must be able to withstand pulses up to the clamping protection
provided by the MOV. A metalized polypropylene capacitor, such as the 474MKP275KA from Illinois Capacitor,
Inc., is rated for 50 Hz to 60 Hz, 250 VAC to 310 VAC, and can withstand 24 impulses of 2.5 kV.
Copyright © 2010–2012, Texas Instruments Incorporated 45
Product Folder Link(s): AFE031