CPC7691
Whenever the LATCH enable control pin is at logic 1,
the data latch is active and data is locked. Subsequent
more information. The attributes of ringing switch SW4
may make it possible to eliminate the need for a
zero-cross switching scheme. A minimum impedance
of 300 Ω in series with the ringing generator is
recommended.
IN
input changes will not result in a change to
RINGING
the control logic or affect the existing switch state.
The switches will remain in the state they were in
when the LATCH pin changes from logic 0 to logic 1
and will not respond to changes in input as long as the
2.7 Power Supplies
Both a +5 V supply and battery voltage are connected
to the CPC7691. Switch state control is powered
exclusively by the +5 V supply. As a result, the
CPC7691 exhibits extremely low power consumption
during active and idle states.
LATCH is at logic 1. However, neither the T input
SD
nor the T output control functions are affected by
SD
the latch function. Since internal thermal shutdown
control and external “All-off” control is not affected by
the state of the LATCH enable input, T will override
SD
state control.
Although battery power is not used for switch control, it
is required to supply trigger current for the integrated
internal protection circuitry SCR during fault
2.5 T Pin Description
SD
conditions. This integrated SCR is designed to
The T pin is a bi-directional I/O structure with an
SD
activate whenever the voltage at T
or R
drops 2
BAT
BAT
internal pull-up current source with a nominal value of
16 μA biased from V
to 4 V below the applied voltage on the V
pin.
BAT
.
DD
Because the battery supply at this pin is required to
source trigger current during negative overvoltage
fault conditions at tip and ring, it is important that the
net supplying this current be a low impedance path for
high speed transients such as lightning. This will
permit trigger currents to flow enabling the SCR to
activate and thereby prevent a fault induced negative
As an output, this pin indicates the status of the
thermal shutdown circuitry. Typically, during normal
operation, this pin will be pulled up to V but under
fault conditions that create excess thermal loading the
CPC7691 will enter thermal shutdown and a logic low
will be output.
DD
overvoltage event at the T
or R
nodes.
BAT
BAT
As an input, the T pin is utilized to place the
SD
CPC7691 into the “All-Off” state by simply pulling the
input low. For applications using low-voltage logic
2.8 Battery Voltage Monitor
The CPC7691 also uses the V
pin to monitor
BAT
devices (lower than V ), Clare recommends the use
DD
battery voltage. If system battery voltage is lost, the
CPC7691 immediately enters the all-off state. It
remains in this state until the battery voltage is
restored. The device also enters the all-off state if the
system battery voltage goes more positive than –10 V,
and remains in the all-off state until the battery voltage
goes more negative than –15 V. This battery monitor
feature draws a small current from the battery (less
than 1 μA typical) and will add slightly to the device’s
overall power dissipation.
of an open-collector or an open-drain type output to
control T . This avoids sinking the T pull up bias
SD
SD
current to ground during normal operation when the
all-off state is not required. In general, Clare
recommends all applications use an open-collector or
open-drain type device to drive this pin.
2.6 Ringing Switch Zero-Cross Current Turn Off
After the application of a logic input to turn SW4 off,
the ringing switch is designed to delay the change in
state until the next zero-crossing. Once on, the switch
requires a zero-current cross to turn off, and therefore
should not be used to switch a pure DC signal. The
switch will remain in the on state no matter the logic
input until the next zero crossing. These switching
characteristics will reduce and possibly eliminate
overall system impulse noise normally associated with
ringing switches. See Clare application note AN-144,
Impulse Noise Benefits of Line Card Access Switches for
This monitor function performs properly if the
CPC7691 and SLIC share a common battery supply
origin. Otherwise, if battery is lost to the CPC7691 but
not to the SLIC, then the V
pin will be internally
BAT
biased by the potential applied at the T
pins via the internal protection circuitry SCR trigger
current path.
or R
BAT
BAT
R00E
PRELIMINARY
13
CLARE [ CLARE ]
