Si3220/Si3225
Ringing Generation
The Si3220-based Dual ProSLIC chipset provides a
balanced ringing waveform with or without dc offset.
The ringing frequency, cadence, waveshape, and dc
offset are register-programmable.
RLOOP
+
ROUT
Using a balanced ringing scheme, the ringing signal is
applied to both the TIP and the RING lines using ringing
waveforms that are 180° out of phase with each other.
The resulting ringing signal seen across TIP-RING is
twice the amplitude of the ringing waveform on either
the TIP or the RING line, which allows the ringing
circuitry to withstand half the total ringing amplitude
seen across TIP-RING.
RLOAD
VTERM
VRING
–
Figure 24. Simplified Loop Circuit During
Ringing
VRING
The following equation can be used to determine the
TIP-RING ringing amplitude required for a specific load
and loop condition:
RING
VOFF
SLIC
TIP
RLOAD
(RLOAD + RLOOP + ROUT
---------------------------------------------------------------------
×
VTERM = VRING
VTIP
)
where
GND
RLOOP= (0.09 Ω per foot for 26AWG wire)
VCM
VTIP
V PK
ROUT = 320 Ω
VOFF
and
7000 Ω
-------------------
=
RLOAD
#REN
When ringing longer loop lengths, adding a dc offset
voltage is necessary to reliably detect a ring trip
condition (off-hook phone). Adding dc offset to the
ringing signal decreases the maximum possible ringing
amplitude. Adding significant dc offset also increases
the power dissipation in the Si3200 and may require
additional airflow or modified PCB layout to maintain
acceptable operating temperatures in the line feed
circuitry. The Dual ProSLIC chipset automatically
VOV
VRING
VBATH
Figure 23. Balanced Ringing
An internal ringing scheme provides >40 Vrms into a 5
REN load at the terminal equipment using a user-
provided ringing battery supply. The specific ringing
supply voltage required depends on the desired ringing
voltage. The ringing amplitude at the terminal
equipment also depends on the loop impedance and
the load impedance in REN. The simplified circuit in
Figure 24 shows the relationship between loop
impedance and load impedance.
applies and removes the ringing signal during V
-
OC
crossing periods to reduce noise and crosstalk to
adjacent lines. Table 28 provides a list of registers
required for internal ringing generation
46
Rev. 1.0
SILICONIMAGE [ Silicon image ]
