Si3056
Si3018/19/10
Table 17. AC Termination Settings for the Si3010
and Si3018 Line-Side Devices
TBR21 DCT Mode
45
40
35
30
25
20
15
10
5
ACT ACT2
AC Termination
0
0
Real, nominal 600 Ω termination that sat-
isfies the impedance requirements of
FCC part 68, JATE, and other countries.
1
0
0
1
Complex impedance that satisfies global
impedance requirements.
Complex impedance that satisfies global
impedance requirements EXCEPT New
Zealand. Achieves higher return loss for
countries requiring complex ac termina-
tion. [220 Ω + (820 Ω || 120 nF) and
220 Ω + (820 Ω || 115 nF)]
.015 .02 .025 .03 .035 .04 .045 .05 .055 .06
Loop Current (A)
Figure 21. TBR21 Mode I/V Characteristics,
DCV[1:0] = 11, MINI[1:0] = 00, ILIM = 1
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/RING voltage of
the DAA. These bits permit important trade-offs for the
system designer. Increasing the TIP/RING voltage
provides more signal headroom, while decreasing the
TIP/RING voltage allows compliance to PTT standards
in low-voltage countries such as Japan. Increasing the
minimum operational loop current above 10 mA also
increases signal headroom and prevents degradation of
the signal level in low-voltage countries.
Finally, Australia has separate dc termination
requirements for line seizure versus line hold. Japan
mode may be used to satisfy both requirements.
However, if a higher transmit level for modem operation
is desired, switch to FCC mode 500 ms after the initial
off-hook. This satisfies the Australian dc termination
requirements.
1
1
Complex impedance for use in New
Zealand. [370 Ω + (620 Ω || 310 nF)]
Table 18. AC Termination Settings for the
Si3019 Line-Side Device
ACIM[3:0]
0000
AC Termination
600 Ω
900 Ω
0001
0010
270 Ω + (750 Ω || 150 nF) and 275 Ω
+ (780 Ω || 150 nF)
0011
220 Ω + (820 Ω || 120 nF) and
220 Ω + (820 Ω || 115 nF)
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
370 Ω + (620 Ω || 310 nF)
320 Ω + (1050 Ω || 230 nF)
370 Ω + (820 Ω || 110 nF)
275 Ω + (780 Ω || 115 nF)
120 Ω + (820 Ω || 110 nF)
350 Ω + (1000 Ω || 210 nF)
200 Ω + (680 Ω || 100 nF)
600 Ω + 2.16 µF
5.12. AC Termination
The Si3056 has four ac termination impedances with
the Si3018 line-side device and sixteen ac termination
impedances with the Si3019 line-side device. The ACT
and ACT2 bits select the ac impedance on the Si3018
line-side device. The ACIM[3:0] bits select the ac
impedance on the Si3019. The available ac termination
settings are listed for the line-side devices in Tables 17
and 18.
The most widely used ac terminations are available as
register options to satisfy various global PTT
requirements. The real 600 Ω impedance satisfies the
requirements of FCC part 68, JATE, and many other
countries. The 270 Ω+ (750 Ω || 150 nF) satisfies the
requirements of TBR21 (ACT = 0, ACT = 1, or ACIM
[3:0] = 0010).
900 Ω + 1 µF
900 Ω + 2.16 µF
600 Ω + 1 µF
Global complex impedance
28
Rev. 1.05
SILICON [ SILICON ]
