CPC7695_12 Datasheet, PDF (18/25 Pages) IXYS Corporation – Line Card Access Switch

INTEGRATED CIRCUITS DIVISION
PRELIMINARY
CPC7695
Start up scenario 4 will start up with all switches in the
All-Off state but upon the acceptance of a valid V_DD
the LCAS will revert to any one of the legitimate states
listed in the truth tables and there after may randomly
change states based on input pin leakage currents
and loading. Because the LCAS state after power-up
can not be predicted with this start up condition it
should never be utilized.
On designs that do not wish to individually control the
LATCH pins of multi-port cards it is possible to bus
many (or all) of the LATCH pins together to create a
single board level input enable control.
2.6 V_BAT Pin
and SW4 are opened (broken) before the switch
contacts of SW1 and SW2 are closed (made). With
the CPC7695, make-before-break and
break-before-make operations can easily be
accomplished by applying the proper sequence of
logic-level inputs to the device.
The logic sequences for either mode of operation are
given in “Make-Before-Break Operation Logic Table
(Ringing to Talk Transition)” on page 19,
“Break-Before-Make Operation Logic Table (Ringing to Talk
Transition)” on page 19 and “Alternate Break-Before-Make
Operation Logic Table (Ringing to Talk Transition)” on
page 20. Logic states and explanations are shown in
“Truth Tables” on page 15.
2.6.1 Protection
2.6.2 Battery Voltage Monitor
The CPC7695 also uses the V_BAT pin to monitor
battery voltage. If the system battery voltage is lost,
the CPC7695 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 –10V
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 A typical) and will add slightly to the device’s
overall power dissipation.
2.7.1 Make-Before-Break Operation
To use make-before-break operation, change the logic
inputs from the Ringing state directly to theTalk state.
Application of theTalk state opens the ringing return
switch, SW3, as the break switches SW1 and SW2
close. The ringing switch, SW4, remains closed until
the next zero-crossing of the ringing current. While in
the make-before-break state, ringing potentials in
excess of the CPC7695 protection circuitry thresholds
will be diverted away from the SLIC.
This monitor function performs properly if the
CPC7695 and SLIC share a common battery supply
origin. Otherwise, if battery is lost to the CPC7695 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.
2.7 Ringing To Talk State Switch Timing
The CPC7695 provides, when switching from the
Ringing state to theTalk state, the ability to control the
release timing of the ringing switches SW3 and SW4
relative to the state of the break switches SW1 and
SW2 using simple TTL logic-level inputs. The two
available techniques are referred to as
make-before-break and break-before-make operation.
When the switch contacts of SW1 and SW2 are closed
(made) before the ringing switch contacts of SW3 and
SW4 are opened (broken), this is referred to as
make-before-break operation. Break-before-make
operation occurs when the ringing contacts of SW3
18
PRELIMINARY
R00F