CPC7595 Datasheet, PDF (19/25 Pages) Clare, Inc. – Line Card Access Switch

CPC7595
As an input, the T_SD pin can be utilized to place the
CPC7595 into the “All-Off” state by simply pulling the
input low via an open-collector type buffer. Using a
standard output with an active logic high drive
capability will sink the pull-up current resulting in
unnecessary power consumption.
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
overvoltage event at the T_BAT or R_BAT nodes.
Use of a standard output buffer with an active high
2.8 Battery Voltage Monitor
drive capability will not disable the thermal shutdown
The CPC7595 also uses the V_BAT pin to monitor
mechanism. The ability to enter thermal shutdown
during a fault condition is independent of the
connection at the T_SD input.
y _{The CPC7595’s internal pull up has a nominal value of}
r ^16μA.
a _{2.6 Ringing Switch Zero-Cross Current Turn Off}
After the application of a logic input to turn SW4 off,
in ^{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
lim ^{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
e _{more information. The attributes of ringing switch SW4}
may make it possible to eliminate the need for a
r _{zero-cross switching scheme. A minimum impedance}
of 300 Ω in series with the ringing generator is
P ^recommended.
battery voltage. If the system battery voltage is lost,
the CPC7595 immediately enters the all-off state. It
remains in this state until the system battery voltage is
restored. The device also enters the all-off state if the
battery voltage rises more positive than about –10 V
and remains in the all-off state until the battery voltage
drops below –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.
This monitor function performs properly if the
CPC7595 and SLIC share a common battery supply
origin. Otherwise, if battery is lost to the CPC7595 but
not to the SLIC, the V_BAT pin will be internally biased
by the potential applied to the T_BAT or R_BAT pins via
the internal protection circuitry SCR trigger current
path.
2.9 Protection
2.9.1 Diode Bridge/SCR
The CPC7595 uses a combination of current limited
break switches, a diode bridge/SCR clamping circuit,
and a thermal shutdown mechanism to protect the
2.7 Power Supplies
Both a +5 V supply and battery voltage are connected
to the CPC7595. Switch state control is powered
exclusively by the +5 V supply. As a result, the
CPC7595 exhibits extremely low power consumption
during active and idle states.
SLIC device or other associated circuitry from damage
during line transient events such as lightning. During a
positive transient condition, the fault current is
conducted through the diode bridge to ground via
F_GND. Voltage is clamped to a diode drop above
ground. During a negative transient of 2 to 4 V more
negative than the voltage source at V_BAT, the SCR
Although battery power is not used for switch control, it
conducts and faults are shunted to F_GND via the SCR
is required to supply trigger current for the integrated
or the diode bridge.
internal protection circuitry SCR during fault
conditions. This integrated SCR is designed to
In order for the SCR to crowbar or foldback, the SCR’s
activate whenever the voltage at T_BAT or R_BAT drops 2
to 4 V below the applied voltage on the V_BAT pin.
Because the battery supply at this pin is required to
source trigger current during negative overvoltage
on-voltage (see “Protection Circuitry Electrical
Specifications” on page 13) must be less than the
applied voltage at the V_BAT pin. If the V_BAT voltage is
less negative than the SCR on-voltage, or if the V_BAT
fault conditions at tip and ring, it is important that the
supply is unable to source the trigger current, the SCR
will not crowbar.
R00B
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