Si3210/Si3211/Si3212
leakages, etc. The total I
smaller than 80 mA.
current should be Register 40 should be set with the calculated V
provide voltage headroom during ringing.
to
OVR
LOAD,PK
Silicon revisions C and higher support the option to
briefly increase the maximum differential current limit
between the voltage transition of TIP and RING from
ringing to a dc linefeed state. This mode is enabled by
setting ILIMEN = 1 (direct Register 108, bit 7).
β + 1
------------
VOVR = ILOAD,PK
80.6 Ω + 1 V
β
where β is the minimum expected current gain of
transistors Q5 and Q6.
The minimum value for VBATH is therefore given by the
following:
Ring Trip Detection
A ring trip event signals that the terminal equipment has
gone off-hook during the ringing state. The ProSLIC
performs ring trip detection digitally using its on-chip
monitor A/D converter. The functional blocks required to
implement ring trip detection is shown in Figure 21. The
primary input to the system is the Loop Current Sense
value provided by the current monitoring circuitry and
reported in direct Register 79. LCS data is processed by
the input signal processor when the ProSLIC is in the
ringing state as indicated by the Linefeed Shadow
register (direct Register 64). The data then feeds into a
VBATH = VAC,PK + VROFF + VOVR
The ProSLIC is designed to create a fully balanced
ringing waveform, meaning that the TIP and RING
common mode voltage, (V
+ V
)/2, is fixed. This
TIP
RING
voltage is referred to as VCM_RING and is
automatically set to the following:
VBATH – VCMR
---------------------------------------------
VCM_RING =
2
VCMR is an indirect register which provides the programmable digital low pass filter, which removes
headroom by the ringing waveform with respect to the unwanted ac signal components before threshold
VBATH rail. The value is set as a 4-bit setting in indirect detection.
Register 40 with an LSB voltage of 1.5 V/LSB.
Input
Signal
Processor
LCS
ISP_OUT
Digital
LPF
+
–
DBIRAW
RTIP
RTP
Debounce
Filter
Interrupt
Logic
NRTP
RTDI
RTIE
LFS
Ring Trip
Threshold
RPTP
Figure 21. Ring Trip Detector
The output of the low pass filter is compared to a trip condition.
programmable threshold, RPTP (indirect Register 29).
The recommended values for RPTP, NRTP, and RTDI
vary according to the programmed ringing frequency.
Register values for various ringing frequencies are
given in Table 30.
The threshold comparator output feeds a programmable
debouncing filter. The output of the debouncing filter
remains in its present state unless the input remains in
the opposite state for the entire period of time
programmed by the ring trip debounce interval,
RTDI[6:0] (direct Register 70). If the debounce interval
has been satisfied, the RTP bit of direct Register 68 will
be set to indicate that a valid ring trip has occurred. A
ring trip interrupt is generated if enabled by the RTIE bit
(direct Register 22). Table 29 lists the registers that
must be written or monitored to correctly detect a ring
36
Preliminary Rev. 1.11
ETC [ ETC ]
