CPC7583
(TSD) as a control are 0 which forces the device to the “all
off state” or float which allow logic inputs to remain active.
This may require use of an open collector buffer.
less negative the SCR on voltage, the SCR will not crow-
bar, 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 directed to ground. The
negative cycle of the transient will cause the SCR to con-
duct when the voltage exceeds the battery reference volt-
age by two to four volts, steering the current to ground.
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 signal. The switch will remain in
the on state no matter what logic input until the next zero
crossing. These switching characteristics will reduce and
possibly eliminate overall system impulse noise normally
associated with ringing access switches. The attributes of
ringing access switch may make it possible to eliminate
the need for a zero cross switching scheme. A minimum
impedance of 300Ω in series with the ring generator is
recommended.
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 ap-
plied to the line though a properly clamped external pro-
tector, the current seen at pins 6 (TBAT) and pin 23 (RBAT) will
be a pulse with a typical magnitude and duration of 2.5A
and < 0.5ms.
Power Supplies
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 lim-
ited by the dynamic DC current limit response of the two
break switches. The DC current limit, specified over tem-
perature, is between 80mA and 400mA and the circuitry
has a negative temperature coefficient. As a result, if the
device is subjected to extended heating due to power cross
Both a +5V supply and battery voltage are connected to
the CPC7583. CPC7583 switch state control is powered
exclusively by the +5V supply. As a result, the CPC7583
exhibits extremely low power dissipation during both active
and idle states.
Battery Voltage Monitor
The CPC7583 also uses the voltage reference to monitor
battery voltage. If battery voltage is lost, the CPC7583 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) and will add slightly to the
device’s overall power dissipation.
fault, the measured current at pin 6 (TBAT) and pin 23 (RBAT
)
will decrease as the device temperature increases. If the
device temperature rises sufficiently, the temperature shut-
down 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 110ϒC placing
the device in the “all off” state regardless of logic input.
During this thermal shutdown mode, pin 13 (TSD) will read
Protection
0V. Normal output of TSD is +V .
DD
Diode Bridge/SCR
The CPC7583 uses a combination of current limited break
switches, a diode bridge/SCR clamping circuit and a ther-
mal shutdown mechanism to protect the SLIC device or
other associated circuitry from damage during line tran-
sient events such as lightning. During a positive transient
condition, the fault current is conducted through the diode
bridge and to ground. During a negative transient of two or
four volts more negative than the battery, the SCR con-
ducts and faults are shunted to ground via the SCR and
diode bridge.
If presented with a short duration transient such as a light-
ning event, the thermal shutdown feature will not typically
activate. But in an extended power cross transient, the
device temperature will rise and the thermal shutdown will
activate forcing the switches to an “all off” state. At this
point the current measured at pin 6 (TBAT) and pin 23 (RBAT
)
will drop to zero. Once the device enters thermal shut-
down it will remain in the “all off” state until the temperature
of the device drops below the activation level of the ther-
mal shutdown circuit. This will return the device to the state
prior to thermal shutdown. If the transient has not passed,
current will flow at the value allowed by the dynamic DC
current limiting of the switches and heating will begin again,
reactivating the thermal shutdown mechanism. This cycle
Also, in order for the SCR to crowbar or foldback, the on
voltage (see Table 11) of the SCR must be less negative
than the battery reference voltage. If the battery voltage is
Rev. E
12
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