Si3220/Si3225
supplies power to the desired channel.
Automatic Dual Battery Switching
The BATSEL pins for both channels are controlled using
the BATSEL bit of the RLYCON register and can be
programmed to automatically switch to the lower battery
The Dual ProSLIC chipsets provide the ability to switch
between several user-provided battery supplies to aid
thermal management. Two specific scenarios where
this method may be required follow:
supply (V
) when the off-hook TIP-RING voltage is
BLO
low enough to allow proper operation from the lower
supply. When using the Si3220, this mode should
always be enabled to allow seamless switching
between the ringing and off-hook states. The same
switching scheme is used with the Si3225 to reduce
power by switching to a lower off-hook battery when
sourcing a short loop.
ꢀ Ringing to off-hook state transition (Si3220):
During the on-hook operating state, the Dual
ProSLIC chipset must operate from the ringing
battery supply to provide the desired ringing signal
when required. Once an off-hook condition is
detected, the Dual ProSLIC chipset must transition
to the lower battery supply, typically –24 V, to reduce
power dissipation during the active state. The low
current consumed by the Dual ProSLIC chipset
during the on-hook state results in very little power
dissipation while being powered from the ringing
battery supply, which can have an amplitude as high
as –100 V depending on the desired ringing
amplitude.
ꢀ On-hook to off-hook state, short loop feed
(Si3225): When sourcing both long and short loop
lengths, the Dual ProSLIC chipset can automatically
switch from the typical –48 V off-hook battery supply
to a lower off-hook battery supply (e.g., –24 V) to
reduce the total off-hook power dissipation. The Dual
ProSLIC chipset continuously monitors the TIP-
RING voltage and selects the lowest battery voltage
required to power the loop when transitioning from
the on-hook to the off-hook state, thus assuring the
lowest power dissipation.
Two thresholds are provided to enable battery switching
with hysteresis. The BATHTH RAM location specifies
the threshold at which the Dual ProSLIC device
switches from the low battery (V
) to the high battery
BLO
(V ) due to an off-hook-to-on-hook transition. The
BHI
BATLTH RAM location specifies the threshold at which
the Si3220/Si3225 switches from V
to V
due to a
BLO
BHI
transition from the on-hook or ringing state to the off-
hook state or because the overhead during active Off-
Hook mode is sufficient to feed the subscriber loop
using a lower battery voltage.
The low-pass filter coefficient is calculated using the
following equation and is entered into the BATLPF RAM
location:
3
BATLPF = [(2πf x 4096)/800] x 2
Where f = the desired cutoff frequency of the filter
The programmable range of the filter is from 0h (blocks
all signals) to 4000h (unfiltered). A typical value of
10 Hz (0A10h) is sufficient to filter out any unwanted ac
artifacts while allowing the dc information to pass
through the filter.
The BATSELa and BATSELb pins switch between the
two battery voltages based on the operating state and
the TIP-RING voltage. Figure 19 illustrates the chip
connections required to implement an automatic dual
battery switching scheme. When BATSEL is pulled
Table 22 provides the register and RAM locations used
for programming the battery switching functions.
LOW, the desired channel is powered from the V
BLO
supply. When BATSEL is pulled HIGH, the V
source
BHI
Table 22. Register and RAM Locations Used for Battery Switching
Parameter
Register/RAM
Mnemonic
Register/RAM Programmable
Bits Range
Resolution
(LSB Size)
High Battery Detect Threshold
Low Battery Detect Threshold
BATHTH
BATHTH[14:7] 0 to 160.173 V*
628 mV
(4.907 mV)
BATLTH
BATLTH[14:7]
0 to 160.173 V*
628 mV
(4.907 mV)
Ringing Battery Switch (Si3220 only)
Battery Select Indicator
Battery Switching LPF
RLYCON
RLYCON
BATLPF
GPO
BSEL
BATLPF[15:3]
Toggle
Toggle
0 to 4000h
N/A
N/A
N/A
*Note: Usable range for BATHTH and BATLTH is limited to the VBHI voltage.
40
Rev. 1.0
SILICONIMAGE [ Silicon image ]
