Agere Communications Inc.
19
Data Sheet
September 2001
L7585G Full-Feature, Low-Power SLIC and Switch
Applications
(continued)
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 500
, as shown in Figure 4, will set
the ring trip current threshold to ±6.0 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
BAT
) or a negative-going zero crossing
(between –10 V and –20 V at –50 V V
BAT
). The different
threshold for positive-going and negative-going zero
crossings is the result of hysteresis of approximately
20 V.
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
BAT
) or a negative-going zero crossing
(between –10 V and –20 V at –50 V V
BAT
). The different
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.
False On-Hook Transients
I
If the L7585G is off-hook in the ground-start/tip open
state, the ground-start/tip ground state, or the
ground-start/tip amplifier state, due to an applied ring
ground, and it is switched to the forward battery
active state, it will not generate a false on-hook
longer than 10 ms in duration. This applies for loop
resistances of 0
to 2000
,
providing that all of the
following criteria are satisfied:
— A loop closure is applied before the L7585G
switches to the forward battery active state.
— The loop closure resistance (telephone set) is less
than 430
.
— The ring ground and loop closure are applied at
the same end of the loop.
— If the ring ground is removed while the L7585G is
in the forward battery active state, then the ring
ground resistance must be greater than 225
when the dc current limit is 40 mA, or greater than
430
when the dc current is 28 mA.