SI3232-KQ Silicon Laboratories Inc, SI3232-KQ Datasheet - Page 39

• Manufacturer Part Number: SI3232-KQ
• Description: IC SLIC PROG DUAL-CH 64TQFP
• Manufacturer: Silicon Laboratories Inc

Specifications of SI3232-KQ

• Package / Case: *
• Function: Subscriber Line Interface Concept (SLIC)
• Interface: ISDN
• Number Of Circuits: 2
• Voltage - Supply: 3.13 V ~ 3.47 V
• Current - Supply: 28mA
• Power (watts): 280mW
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Product: SLIC
• Supply Voltage (min): 3.13 V
• Supply Current: 28 mA
• Maximum Operating Temperature: + 70 C
• Minimum Operating Temperature: 0 C
• Mounting Style: SMD/SMT
• Number Of Channels: 2
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Ring Trip Detection
A ring trip event signals that the terminal equipment has
transitioned to an off-hook condition after ringing has
commenced, thus ensuring that the ringing signal is
removed before normal speech begins. The Si3232 is
designed to implement either an ac- or dc-based
internal ring trip detection scheme or a combination of
both schemes. This allows system-design flexibility for
addressing
applications. An ac ring trip detection scheme cannot
reliably detect an off-hook condition when sourcing
longer loop lengths, as the 20 Hz ac impedance of an
off-hook long loop is indistinguishable from a heavily-
loaded (5 REN) short loop in the on-hook state.
Because of this situation, a dc ring trip detection
scheme is required when sourcing longer loop lengths.
The Si3232 can implement either an ac- or dc-based
ring trip detection scheme depending on the application.
Table 23 on page 41 lists the registers that must be
written or monitored to correctly detect a ring trip
condition.
The Si3232 provides the ability to process a ring trip
event using only an ac-based detection scheme. Using
this scheme eliminates the need for adding dc offset to
the ringing signal, which reduces the total power
dissipation during the ringing state and maximizes the
available ringing amplitude. This scheme is only valid
for shorter loop lengths, as it may not be possible to
reliably detect a ring trip event if the off-hook line
impedance overlaps the on-hook impedance at 20 Hz.
The Si3232 also provides the ability to add a dc offset
component to the ringing signal and detect a ring trip
event by monitoring the dc loop current flowing once the
terminal equipment transitions to the off-hook state.
Although adding dc offset reduces the maximum
available ringing amplitude (using the same ringing
supply), this method is required to reliably detect a valid
ring trip event when sourcing longer loop lengths. The
dc offset can be programmed from 0 to 63.3 V in the
RINGOF RAM address as required to produce
R
I
OUT
DD,OH
R
LOAD
=
varying
R
=
Si3232 ouput impedance
LOOP
I
DD
=
7000
------------ - (for North America)
REN
overhead current
=
loop
loop impedance
lengths
=
=
12 mA
320Ω
of
Preliminary Rev. 0.95
different
adequate dc loop current in the off-hook state.
Depending on the loop length and the ring trip method
desired, the ac or dc ring trip detection circuits can be
disabled by setting their respective ring trip thresholds
(RTACTH or RTDCTH) sufficiently high so it will not trip
under any condition.
Figure 20 illustrates the internal functional blocks that
serve to correctly detect and process a ring trip event.
The primary input to the system is the loop current
sense (ILOOP) value provided by the loop monitoring
circuitry and reported in the ILOOP RAM location
register. This ILOOP register value is processed by the
input signal processor block provided that the LFS bits
in the Linefeed register value indicate the device is in
the ringing state. The output of the input signal
processor then feeds into a pair of programmable digital
low-pass filters; one for the ac ring trip detection path
and one for the dc path. The ac path also includes a full-
wave rectifier block prior to the LPF block. The outputs
of each low-pass filter block are then passed on to a
programmable ring trip threshold (RTACTH for ac
detection and RTDCTH for dc detection). Each
threshold block output is then fed to a programmable
debounce filter that ensures a valid ring trip event. The
output of each debounce filter remains constant unless
the input remains in the opposite state for the entire
period of time set using the ac and dc ring trip debounce
interval registers, RTACDB and RTDCDB, respectively.
The outputs of both debounce filter blocks are then
ORed together. If either the ac or the dc ring trip circuits
indicate a valid ring trip event has occurred, the RTP bit
is set. Either the ac or dc ring trip detection circuits can
be disabled by setting the respective ring trip threshold
sufficiently high so it will not trip under any condition. A
ring trip interrupt is also generated if the RTRIPE bit has
been enabled.
Ring Trip Timeout Counter
The Dual ProSLIC incorporates a ringtrip timeout
counter, RTCOUNT, that monitors the status of the
ringing control. When exiting ringing, the Dual ProSLIC
will allow the ringtrip timeout counter amount of time
(RTCOUNT x 1.25 ms/LSB) for the mode to switch to
On-hook Transmission or Active. The mode that is
being exited to is governed by whether the command to
exit ringing is a ringing active timer expiration (on-hook
transmission) or ringtrip/manual mode change (Active
mode). The ringtrip timeout counter will assure ringing is
exited within its time setting (RTCOUNT x 1.25 ms/LSB,
typically 200 ms).
Si3232
39