Although the series coupling
impedance is minimized to
reduce insertion loss, it has to
be sufficiently large to limit
the peak current to the
desired level in the worst
expected powerline load
condition. The peak output
current is effectively limited by
the total series coupling
resistance, which is made up
of the series resistance of L2,
the series resistance of the
fuse and any other resistive
element connected in the
coupling network.
necessary to add an external
6.8 V bi-directional transient
voltage protector (as
component D1 shown in Figure driver circuit will be shut
17).
temperature stress. Should the
IC junction temperature reach
a level above 150°C, the line
down and the output of Status
(pin 1) is pulled to the logic
high state simultaneously.
Additional protection from
powerline voltage surges can
be achieved by adding an
appropriate Metal Oxide
Varistor (MOV) across the
powerline terminals after the
fuse.
The final feature is load
detection function. The
powerline impedance is quite
unpredictable and varies not
just at different connection
points but is also time variant.
The HCPL-8100 and HCPL-
0810 include a current sense
feature, which may be utilized
to feedback information on the
instantaneous powerline load
condition. Should the peak
current reach a level greater
Internal Protection and Sensing
The HCPL-8100 and HCPL-
0810 include several sensing
and protection functions to
ensure robust operation under
wide ranging environmental
conditions.
To reduce power dissipation
when not operating in transmit
mode the line driver stage is
shut down to a low power
high impedance state by
than 0.5 A , the output of
PP
pulling the Tx-en input (pin 2) The first feature is the V
status pin is pulled to a logic
CC
to logic low state.
Under Voltage Detection (UVD). high state for the entire period
In the event of V dropping
the peak current exceeds -0.25
A as shown in Figure 12.
Using the period of the pulse
together with the known
CC
External Transient Voltage
Protection
to a voltage less than 4 V, the
output status pin is switched
to a logic high state.
To protect the HCPL-8100 and
HCPL-0810 from high voltage
transients caused by power
surges and disconnecting/
connecting the modem, it is
coupling impedance, the actual
powerline load can be
calculated. Table 2 shows the
logic output of the Status pin.
The next feature is the over-
temperature shutdown. This
particular feature protects the
line driver stage from over-
Table 2. Status pin logic
Normal
VCC < 4 V
Over-Temperature
ITx-out < − 0.25 A
Status output
Low
High
High
High (pulsed)
HP [ HEWLETT-PACKARD ]
