Le75183
Data Sheet
9.0 Switching Behavior
When switching from the power ringing state to the idle/talk state via simple logic level input control, the Le75183 is
able to provide control with respect to the timing when the ringing access contacts are released relative to the state
of the line break contacts.
Make-before-break operation occurs when the line break switch contacts are closed (or made) before the ringing
access switch contact is opened (or broken). Break-before-make operation occurs when the ringing access contact
is opened (broke) before the line break switch contacts are closed (made).
Using the logic level input pins INRING, INTESTin, and INTESTout, either make-before-break or break-before-make
operation of the Le75183 is easily achieved. The logic sequences for either mode of operation are given in Table 13
and Table 14. See the Truth Tables (Table 16 and Table 17) for an explanation of logic states.
When using an Le75183 in the make-before-break mode, during the ring-to-idle transition, for a period of up to
one-half the ringing frequency, the ring break switch and the pnpn-type ring access switch can both be in the ON
state. This is the maximum time after the logic signal at INRING has transitioned that the ring access switch is
waiting for the next zero current cross, so it can close. During this interval, current that is limited to the dc break
switch current-limit value will be source from the ring node of the SLIC.
This current is presented to the internal protection circuit. If the SCR-type protector is used (A or C codes), if by
random probability the ring-to-idle transition occurs during a portion of the ring cycle when the ringing voltage
exceeds the protection circuit SCR turn-on voltage, and if current in excess of the SCR’s turn-on current is also
available, the SCR may turn on. Once the SCR is triggered on, if the SLIC is capable of supplying current in excess
of the holding current, the SCR may be latched on by the SLIC.
The probability of this event depends on the characteristics of the given SLIC and of the holding current of the
Le75183 A or C device. The SCR hold current distribution is designed to be safely away from the test limit of 80
mA. The higher the distribution, the lower the probability of the latch.
If this situation is of concern for a given board design, either use the A or C series device in the break-before-make
mode (eliminates the original 25 ms current pulse) or use a B series device (eliminates the SCR).
Break
Switches
3 & 4
Ring
Return
Switch 7
Ring
Access
Switch 8
All Other
Access
Switches
INRING
INTESTin
INTESTout
TSD
State
Power
Timing
1
0
0
1/Float
—
Open
Closed
Closed
Closed
Open
Open
Closed
Closed
Open
Open
Open
Open
Ringing
SW8 waiting for next zero
current crossing to turn off
maximum time—one-half
of ringing. In this transition
state, current that is limited
to the dc break switch
current-limit value will be
sourced from the ring node
of the SLIC.
Make-bef
ore-break
0
0
0
0
0
0
1/Float
1/Float
Zero cross current has
occurred.
Idle/Talk
Table 9 - Make-Before-Break Operation
16
Zarlink Semiconductor Inc.
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
