CPC7582 Datasheet, PDF (9/12 Pages) Clare, Inc. – Line Card Access Switch

CPC7582
Ring Access Switch Zero Cross Current Turn Off
After the application of a logic input to turn SW4 off,
the ring access 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 sig-
nal. The switch will remain in the on state no matter
what logic input until the next zero crossing. For prop-
er operation, pin 13 (R_Ring) should be connected using
proper impedance to a ring generator or other ac
source. These switching characteristics will reduce
and possibly eliminate overall system impulse noise
normally associated with ringing access switches. The
attributes of ringing access switch SW4 may make it
possible to eliminate the need for a zero cross switch-
ing scheme. A minimum impedence of 300Ω in series
with the ring generator is recommended.
Power Supplies
Both a +5V supply and battery voltage are connected
to the CPC7582. CPC7582 switch state control is
powered exclusively by the +5V supply. As a result,
the CPC7582 exhibits extremely low power dissipa-
tion during both active and idle states.
The battery voltage is not used for switch control but
rather as a reference by the integrated secondary pro-
tection circuitry. The integrated SCR is designed to
trigger when pin 2 (T_BAT) or pin 15 (R_BAT) drops 2 to 4V
below the battery. This trigger prevents a fault induced
overvoltage event at the T_BAT or R_BAT nodes.
Battery Voltage Monitor
The CPC7582 also uses the voltage reference to mon-
itor battery voltage. If battery voltage is lost, the
CPC7582 will immediately enter the “all off” state and
remain in this state until the battery voltage is restored.
The device will also enter the “all off” state if the battery
voltage rises above –10V and will remain there until the
battery voltage drops below –15V. This battery monitor
feature draws a small current from the battery (<1µA
typ.) and will add slightly to the device’s overall power
dissipation.
Protection
Diode Bridge/SCR
The CPC7582 uses a combination of current limited
break switches, a diode bridge/SCR clamping circuit
and a thermal shutdown mechanism to protect the
SLIC device or other associated circuitry from damage
during line transient events such as lightning. During a
positive transient condition, the fault current is con-
ducted through the diode bridge to ground. Voltage is
clamped to the diode drop above ground. During a
negative transient of 2 - 4 volts more negative than the
battery, the SCR conducts and faults are shunted to
ground via the SCR and diode bridge.
Also, in order for the SCR to crowbar or foldback, the
on voltage (see Table 8) of the SCR must be less neg-
ative than the battery reference voltage. If the battery
voltage is less negative the SCR on voltage, the SCR
will not crowbar, however it will conduct fault currents to
ground.
For power induction or power cross fault conditions,
the positive cycle of the transient is clamped to the
diode drop above ground and the fault current direct-
ed to ground. The negative cycle of the transient will
cause the SCR to conduct when the voltage exceeds
the battery reference voltage by two to four volts,
steering the current to ground.
Current Limiting function
If a lightning strike transient occurs when the device in
the talk/idle state, the current is passed along the line
to the integrated protection circuitry and limited by the
dynamic current limit response of break switches SW1
and SW2. When a 1000V 10x1000 pulse (LSSGR
lightning) is applied to the line though a properly
clamped external protector, the current seen at pins 2
(T_BAT) and pin 15 (R_BAT) will be a pulse with a typical
magnitude and duration of 2.5A and < 0.5ms.
If a power cross fault occurs with device in the talk/idle
state, the current is passed though the break switches
SW1 and SW2 on to the integrated protection circuit
and is limited by the dynamic DC current limit
response of the two break switches. The DC current
limit, specified over temperature, is between 80mA
and 425mA and the circuitry has a negative tempera-
ture coefficient. As a result, if the device is subjected
to extended heating due to power cross fault, the
measured current at pin 2 (T_BAT) and pin 15 (R_BAT) will
decrease as the device temperature increases. If the
device temperature rises sufficiently, the temperature
shutdown mechanism will activate and the device will
default to the “all off” state.
Temperature Shutdown
The thermal shutdown mechanism will activate when
the device temperature reaches a minimum of 110°C
placing the device in the “all off” state regardless of
logic input. During this thermal shutdown mode, pin 7
(TSD) will read 0V. Normal output of TSD is +V_DD
Rev. 1.0
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