Si3220/Si3225
Table 18. Register and RAM Locations for Linefeed Control
Parameter
Register/
RAM
Register/RAM
Bits
Programmabl LSB Size
e Range
Effective
Resolutio
n
Mnemonic
Linefeed
LINEFEED
LINEFEED
RLYCON
ILIM
LF[2:0]
LFS[2:0]
BATSEL
ILIM[4:0]
VOC[14:0]
See Table 17
Monitor Only
VBATH/VBATL
18–45 mA
0 to 63.3 V
0 to 63.3 V
0 to 63.3 V
0 to 63.3 V
0 to 63.3 V
0 to 63.3 V
0 to 63.3 V
0 to 63.3 V
N/A
N/A
N/A
N/A
N/A
N/A
Linefeed Shadow
Battery Feed Control
Loop Current Limit
On-Hook Line Voltage
Common Mode Voltage
0.875 mA
4.907 mV
4.907 mV
4.907 mV
4.907 mV
4.907 mV
4.907 mV
4.907 mV
4.907 mV
0.875 mA
1.005 V
1.005 V
1.005 V
1.005 V
1.005 V
1.005 V
1.005 V
1.005 V
VOC
VCM
VCM[14:0]
V
V
V
Delta for Off-Hook
Delta Threshold, Low
Delta Threshold, High
VOCDELTA
VOCLTH
VOCHTH
VOV
VOVRING
VOCTRACK
VOCDELTA[14:0]
VOCLTH[15:0]
VOCHTH[15:0]
VOV[14:0]
VOVRING[14:0]
VOCTRACK[15:0]
OC
OC
OC
Overhead Voltage
Ringing Overhead Voltage
V
During Battery Tracking
OC
source. ILIM is a 5-bit register field, which is
programmable from 18 mA to 45 mA in 0.875 mA steps
(i.e., ILIM = 0x0 corresponds to 18 mA and ILIM= 0x1F
corresponds to 45 mA).
Adaptive Linefeed
The Si3220/Si3225 features a proprietary dc feed
design known as adaptive linefeed.
Figure 16 shows the V/I characteristics of adaptive
linefeed. Essentially, adaptive linefeed changes the
source impedance of the dc feed as well as the
apparent open-circuit voltage (VOC) in order to ensure
the ability to source extended loop lengths. The
following sections provide a detailed explanation of
adaptive linefeed.
The following equation is used to calculate VOV, VCM,
VOC, VOCLTH, VOCHTH and VOCDELTA.
desired_voltage 512
RAMValue= DEC2HEX 2⋅CEILINGROUND
⋅
1.005V
5
In the above equation, the ROUND function rounds the
result to the nearest integer while the CEILING function
rounds-up the result to the nearest integer. The
DEC2HEX function converts a decimal integer into a
hexadecimal integer.
The RAM values shown in Table 19 where used to
generate the adaptive linefeed V/I curve shown in
Figure 16. Note that a battery voltage of –56 V was
assumed, as shown in Table 19.
Adaptive Linefeed Example
This section provides a detailed description of adaptive
linefeed operation by utilizing an example. The behavior
of adaptive linefeed is controlled by the following RAM
locations: VOV, VCM, VOC, VOCLTH, VOCHTH and
VOCDELTA (see Equation 1). The ILIM register also
plays a role in determining the behavior of the dc feed
as it sets the current limit for the constant current
Table 19. Adaptive Linefeed Example Values
VBAT
–56 V
VOV
4 V
VCM
3 V
VOC
–48 V
ILIM
20 mA
VOCLTH
–7 V
VOCHTH
VOCDELTA
+2 V
+6 V
32
Rev. 1.0
SILICONIMAGE [ Silicon image ]
