CPC75282 Datasheet, PDF (13/19 Pages) Clare, Inc. – Line Card Access Switch

INTEGRATED CIRCUITS DIVISION
PRELIMINARY
CPC75282
2.3 Switch Logic
2.3.1 Start-up
The CPC75282 uses smart logic to monitor the V_DD
supply. Any time the V_DD is below an internally set
threshold, the smart logic places the control logic to
the all-off state until the LATCH_x input is pulled low.
Prior to the assertion of a logic low at the LATCH_x pin,
the switch control inputs must be properly conditioned.
2.3.2 Switch Timing
With the CPC75282, 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 13 and
“Break-Before-Make Ringing to Talk Transition
Logic Sequence CPC7592xA/B” on page 14. Logic
states and explanations are shown in “Truth Tables”
on page 11.
When switching from the ringing state to the idle/talk
state, the CPC75282 provides the ability to control the
release timing of the ringing switches, SW3 and SW4,
relative to the state of the switches, SW1 and SW2,
using simple logic inputs. The two available
techniques are referred to as make-before-break and
break-before-make operation. When the break 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
and SW4 are opened (broken) before the switch
contacts of SW1 and SW2 are closed (made).
2.3.3 Make-Before-Break Operation
To use make-before-break operation, change the logic
inputs from the ringing state directly to the idle/talk
state. Application of the idle/talk 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 CPC75282
protection circuitry thresholds will be diverted away
from the SLIC.
State
Ringing
Make-
before-
break
Idle/Talk
(CFG=0, P3=0)
P2 P1
1
0
0
0
0
0
2.3.4: Make-Before-Break Operation Logic Table (Ringing to Talk Transition)
LATCH_x
0
OFF_x
1
Timing
Break
Switches
1_x & 2_x
Ringing
Return
Switch
3_x
-
Off
On
SW4 waiting for next zero-current
crossing to turn off. Maximum time is
one-half of the ringing cycle. In this
transition state current limited by the DC
On
Off
break switch current limit value will be
sourced from the ring node of the SLIC.
Zero-cross current has occurred
On
Off
Ringing Test
Switch Switches
4_x
5_x & 6_x
On
Off
On
Off
Off
Off
R00E
PRELIMINARY
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