Section 150-431-114
Release 01
Page 10
6. HDSL LINE VOLTAGE OPTION
6.01
The symmetry of the HDSL line powering voltage
can be set by the S2 switch, located on the printed
circuit board, as shown in Figure 5.
6.02
The factory default setting is unipolar (-). It sets
the HDSL line voltage to 0 V on loop 2 and to
either -130 V (for non-doubler applications) or -200 V (for
doubler applications) on loop 1. This setting keeps the
HDSL cable pair voltage at or below ground potential,
thereby avoiding corrosion problems caused by cable
voltages more positive than ground.
6.03
The bipolar selection sets the HDSL line voltage
to +65 V on loop 2 and -65 V on loop 1, for non-
doubler applications. Doubler applications will have +100
V on loop 2 and -100 V on loop 1. This setting reduces
the maximum ground referenced voltage to 100 V, but
applies positive voltage to the cable pairs, which could
accelerate corrosion on the cable pairs.
6.04
The line voltage power supply, used for both
options, is ground referenced, but also ground
isolated by 200 kohms. This ground isolation reduces
problems due to induced noise currents and large surge
voltages, which are ground referenced. It also reduces
ground fault currents, which improves the product’s safety.
The safety issue thus depends solely on the differential
voltage across loop 1 and loop 2, and is independent of
S2’s setting.
6.05
Jumper JP2 allows the factory burn-in monitor
program to be initiated by applying -48 V to pin
20 during factory testing. If the slot into which the HLU is
located uses pin 20 for any reason, cut the JP2 resistor in
half to avoid unwanted initiation of the factory burn-in
program.
Figure 5. HDSL Line Voltage Switch S2, Factory Burn-In Disable Jumper JP2