LUCL9312AP-D AGERE [Agere Systems], LUCL9312AP-D Datasheet - Page 28

• Manufacturer Part Number: LUCL9312AP-D
• Description: Line Interface and Line Access Circuit Forward Battery SLIC and Ringing Relay for TR-57 Applications
• Manufacturer: AGERE [Agere Systems]

Forward Battery SLIC and Ringing Relay for TR-57 Applications
Supervision
Ring Trip
Ring trip is set by the value of RS1.
The ring trip threshold at the ring trip inputs is ±2.5 V
minimum, ±3.5 V maximum.
A resistor value of 400
the ring trip current threshold to ±7.5 mA typical.
Ring trip is asserted upon entering the ringing mode
until the second zero crossing of ringing. This is either
a positive-going zero crossing (between –40 V and
–30 V at –50 V V
(between –10 V and –20 V at –50 V V
threshold for positive-going and negative-going zero
crossings is the result of hysteresis of approximately
20 V. The act of turning on the switch may or may not
produce a ringing zero crossing, therefore, there may
be a delay of up to almost one cycle of ringing or 50 ms
until NSTAT is high.
Ring trip will not be asserted unless the ring trip thresh-
old is exceeded for two zero crossings. This is either a
positive-going zero crossing (between –40 V and –30 V
at –50 V V
(between –10 V and –20 V at –50 V V
threshold for positive-going and negative-going zero
crossings is the result of hysteresis of approximately
20 V.
Note that since the ringing voltage is monitored at
RSW, one zero crossing can occur at switch turn-on
depending on initial conditions.
Ring trip is asserted immediately if the ring trip input is
15 V ± 3 V.
Switching Behavior
The solid-state ring relay in the L9312 device is able to
provide either make-before-break or break-before-
make timing with respect to switching into and out of
the ring mode. If switching is done directly into and out
of the ring mode, the design of the L9312 will give
make-before-break switching with respect to both the
ring and tip side switches. To achieve break-before-
make switching, the user should via software control
enter an intermediate all-off mode when switching into
and out of the ring mode. The all-off state should be
held a minimum of 8 ms.
Make-Before-Break Operation
The break switches are constructed from DMOS tran-
sistors. The tip side ring return is also a DMOS transis-
28
BAT
) or a negative-going zero crossing
BAT
(continued)
) or a negative-going zero crossing
, as shown in Figure 4, will set
BAT
BAT
). The different
). The different
tor. Because the on resistance of the break switches is
less than the tip side ring return switch, the break
switches are physically bigger. This implies a larger
gate to source capacitance, with inherently slower
switching speeds since it will take longer to charge or
discharge the gate to source capacitance of the break
switches (to change the state of the switch). The ring
access switch is a pnpn type device. The pnpn device
has inherently faster switching speeds than any of the
DMOS type switches.
Going from the active to ring mode, the smaller tip side
ring return switch and the pnpn ring access switch will
change states before the larger break switches. Thus,
the ring contacts are made before the line break
switches are broken: make-before-break operation.
Going from the ring mode to active or scan, the natural
tendency is for the smaller tip side ring return DMOS to
break or open, before the larger DMOS can turn on.
This would not be make-before-break operation on the
tip side. Thus, circuitry is added to speed up charging
of the tip break switch, to speed up the turn on of that
switch to give make-before-break operation on the tip
side.
On the ring side, going from the ring mode to the active
or scan mode, the pnpn will not turn off until the ring
current drops below the hold current of the pnpn device
(which is typically 500 A); this is effectively zero cur-
rent for zero current turn off. This can take up to one-
half cycle of ringing to occur. With this inherent delay in
switching by the pnpn ring access switch, the break
switches will make contact before the ring access
switch breaks contact; so again, make-before-break
switching is achieved.
With the make-before-break switch, there will be a
period of time (depending on ring signal frequency but
measured in tens of microseconds) where all four
switch contacts will be on. This means that the ring
generator will be connected through the current-limited
break switches to the input of the SLIC device. Current
will be limited by the break switch current limit, and this
will not damage the SLIC. This current may, however,
cause a false glitch at the NSTAT supervision output
that will need to be digitally filtered. The board designer
should consider any ramifications of this state on the
overall system or ring generator and battery design.
The major benefit of make-before-break switching is
that it will minimize any impulse noise generated during
ringing cadence. In many cases when operating the
switch in the make-before-break mode, no special
design to switch at zero current and voltage crossing is
required. Impulse noise generation when using solid-
state relays is documented in the Impulse Noise and
the L758X Series of Solid State Switches Application
Note.
Agere Systems Inc.
July 2001