SI2457-D-FS Silicon Laboratories Inc, SI2457-D-FS Datasheet - Page 38

• Manufacturer Part Number: SI2457-D-FS
• Description: IC ISOMODEM SYSTEM-SIDE 16SOIC
• Manufacturer: Silicon Laboratories Inc

Specifications of SI2457-D-FS

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

AN93
3. DAA (Line-Side) Device
The Si3018/10 DAA or line-side device, contains an ADC, a DAC, control circuitry, and an isolation capacitor
interface. The Si3018/10 and surrounding circuitry provide all functionality for telephone line interface requirement
compliance, including a full-wave rectifier bridge, hookswitch, dc termination, ac termination, ring detection, loop
voltage and current monitoring, and call-progress monitoring. The Si3018/10 external circuitry is largely
responsible for EMI, EMC, safety, and surge performance.
3.1. Hookswitch and DC Termination
The DAA has programmable settings for the dc impedance, current limiting, minimum operational loop current, and
Tip-to-Ring voltage. The dc impedance of the DAA is normally represented by a 50  slope as shown in Figure 13,
but can be changed to an 800  slope by setting the DCR bit. This higher dc termination presents a higher
resistance to the line as the loop current increases.
For applications requiring current limiting per the legacy TBR21 standard, the ILIM bit may be set to select this
mode. In this mode, the dc I/V curve is changed to a 2000  slope above 40 mA, as shown in Figure 14. This
allows the DAA to operate with a 50 V, 230  feed, which results in the highest current possible in the old TBR21
standard.
The MINI[1:0] bits select the minimum operational loop current for the DAA, and the DCV[1:0] bits adjust the DCT
pin voltage, which affects the Tip-to-Ring voltage of the DAA. These bits allow important trade-offs to be made
between signal headroom and minimum operational loop current. Increasing the Tip-Ring voltage increases signal
headroom, whereas decreasing the voltage allows compliance to PTT standards in low-voltage countries, such as
Japan or Malaysia. Increasing the minimum operational loop current above 10 mA also increases signal headroom
and prevents degradation of the signal level in low-voltage countries.
38
Figure 14. TBR21 (Legacy) Mode I/V Characteristics
Figure 13. FCC Mode I/V Characteristics
DCV[1:0]
DCV[1:0]
12
11
10
20
8
45
40
35
30
25
15
10
9
7
6
.01 .02 .03 .04 .05 .06 .07 .08 .09 .1 .11
5
.015 .02 .025 .03 .035 .04 .045 .05 .055 .06
=
=
Loop Current (A)
TBR21 DCT Mode
Rev. 1.3
FCC DCT Mode
11, MINI[1:0]
11, MINI[1:0]
Loop Current (A)
=
=
00
00