SI2457-D-FT Silicon Laboratories Inc, SI2457-D-FT Datasheet - Page 40

• Manufacturer Part Number: SI2457-D-FT
• Description: IC ISOMODEM SYSTEM-SIDE 24TSSOP
• Manufacturer: Silicon Laboratories Inc

Specifications of SI2457-D-FT

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

AN93
Bit 15 represents the polarity of the Tip-Ring voltage, and a reversal of this bit represents a Tip-Ring polarity
reversal. LVS = 0x0000 if the Tip-Ring voltage is less than 3.0 V and, in the on-hook state, can be taken as “no line
connected.”
The ISOmodem reports the on-hook line voltage with the LVS bits in two’s complement. LVS has a full scale of 87 V
with an LSB of 1 V. The first code step (going from 0 to 1) is offset so that a 0 indicates a line voltage of less than
3 V. The accuracy of the LVS bits is ±10%. The user can read these bits directly through the LVS register. A typical
transfer function is shown in Figure 15.
When the ISOmodem is off-hook, the LCS bits measure loop current in 1.1 mA/bit resolution. These bits enable the
user to detect another phone going off-hook by monitoring the dc loop current. Line-current sensing is detailed in
Figure 16 and Table 32.
40
128
112
96
80
64
48
32
16
0
0
16
Figure 15. Typical Loop Voltage LVS Transfer Function
32
Tip/Ring Voltage (Volts )
48
Rev. 1.3
64
80
96
112
128