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参数资料
型号： SI3050-E1-FT
厂商： Silicon Laboratories Inc
文件页数： 51/128页
文件大小： 0K
描述： IC VOICE DAA SYSTEM SIDE 20TSSOP
标准包装： 74
系列： *
Si3050 + Si3011/18/19
Rev. 1.5
29
5.12.2. Loop Current Measurement
When the Si3050 is off-hook, the LCS[4:0] bits measure
loop current in 3.3 mA/bit resolution. With the LCS[4:0]
bits, a user can detect another phone going off-hook by
monitoring the dc loop current. The line current sense
transfer function is shown in Figure 21 and is detailed in
Table 14. The LCS and LCS2 bits report loop current
down to the minimum operating loop current for the
DAA. Below this threshold, the reported value of loop
current is unpredictable. The minimum operating loop
current of the DAA is set by the MINI[1:0] bits in
Register 26.
When the LCS bits reach max value, the Loop Current
Sense Overload Interrupt bit (Register 4) fires. LCSOI
firing however, does not necessarily imply that an
overcurrent situation has occurred. An overcurrent
situation in the DAA is determined by the status of the
OPD bit (Register 19). After the LCSOI interrupt fires,
the OPD bit should be checked to determine if an
overcurrent situation exists. The OPD bit indicates an
overcurrent situation when loop current exceeds either
160 mA (ILIM = 0) or 60 mA (ILIM = 1), depending on
the setting of the ILIM bit (Register 26).
The LCS2 register also reports loop current in the
off-hook state. This register has a resolution of 1.1 mA
per bit.
5.13. Off-Hook
The communication system generates an off-hook
command by setting the OH bit (Register 5, bit 0). This
off-hook state seizes the line for incoming/outgoing
calls. It also can be used for pulse dialing.
With the OH bit at logic 0, negligible dc current flows
through the hookswitch. When a logic 1 is written to the
OH bit, the hookswitch transistor pair, Q1 and Q2, turn
on. A termination impedance across TIP and RING is
applied and causes dc loop current to flow. The
termination impedance has both an ac and a dc
component.
Several events occur in the DAA when the OH bit is set.
There is a 250 s latency for the off-hook command to
be communicated to the line-side device. When the
line-side device goes off-hook, an off-hook counter
forces a delay to allow line transients to settle before
transmission or reception can occur. The off-hook
counter time is controlled by the FOH[1:0] bits
(Register 31, bits 6:5).
The
default
setting
for
the
off-hook counter time is 128 ms, but can be adjusted up
to 512 ms or down to 64 or 8 ms.
After the off-hook counter expires, a resistor calibration
is performed for 17 ms to allow the DAA internal
circuitry to adjust to the exact conditions present at the
time of going off-hook. This resistor calibration can be
disabled by setting the RCALD bit (Register 25, bit 5).
After the resistor calibration is performed, an ADC
calibration is performed for 256 ms. This calibration
helps to remove offset in the A/D sampling the
telephone line. ADC calibration can be disabled by
setting the CALD bit (Register 17, bit 5). See "5.6.
Calibration" on page 26 for more information on
automatic and manual calibration.
Silicon Laboratories recommends that the resistor and
the ADC calibrations not be disabled except when a fast
response is needed after going off-hook, such as when
responding to a Type II Caller-ID signal. See "5.25.
Caller ID" on page 36 for detailed information.
To calculate the total time required to go off-hook and
start transmission or reception, include the digital filter
delay (typically 1.5 ms with the FIR filter) in the
calculation.
5.14. Ground Start Support
The Si3050 DAA supports loop-start applications by
default. It can also support ground-start applications
with the RG, TGD, and TGDE pins and the schematic
shown in Figure 22. The component values are listed in
Table 15.
Table 14. Loop Current Transfer Function
LCS[4:0]
Condition
00000
Insufficient line current for normal operation.
Use the DOD bit (Register 19, bit 1) to
determine if a line is still connected.
00100
Minimum line current for normal operation.
(MINI[1:0] = 01)
11111
Loop current may be excessive. Use the
OPD bit to determine if an overload condi-
tion exists.
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