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參數資料
| 型號： | HC5523 |
| 廠商： | Intersil Corporation |
| 英文描述： | LSSGR/TR57 CO/Loop Carrier SLIC with Low Power Standby |
| 中文描述： | LSSGR/TR57文書主任/河套低功耗待機載波用戶接口 |
| 文件頁數： | 8/18頁 |
| 文件大小： | 176K |
| 代理商： | HC5523 |
63
Figure 15 shows the relationship between the saturation
guard voltage, the loop current and the loop resistance.
Notice from Figure 15 that for a loop resistance <1.2k
(R
SG
= 4.0k
) the SLIC is operating in the constant current
feed region and for resistances >1.2k
the SLIC is operating
in the resistive feed region. Operation in the resistive feed
region allows long loop and off-hook transmission by
keeping the tip and ring voltages off the rails. Operation in
this region is transparent to the customer.
The Saturation Guard circuit (Figure 13) monitors the tip to
ring voltage via the transconductance amplifier A
1
. A
1
generates a current that is proportional to the tip to ring
voltage difference. I
1
is internally set to sink all of A
1
’s
current until the tip to ring voltage exceeds 12.5V. When the
tip to ring voltage exceeds 12.5V (with no R
SG
resistor) A
1
supplies more current than I
1
can sink. When this happens
A
2
amplifies its input current by a factor of 12 and the current
through R
1
becomes the difference between I
2
and the
output current from A
2
. As the current from A
2
increases, the
voltage across R
1
decreases and the output voltage on R
DC
decreases. This results in a corresponding decrease in the
loop current. The R
SG
pin provides the ability to increase the
saturation guard reference voltage beyond 12.5V. Equation 3
gives the relationship between the R
SG
resistor value and
the programmable saturation guard reference voltage:
SG
where:
V
SGREF
= Saturation Guard reference voltage.
R
SG
= Saturation Guard programming resistor.
When the Saturation guard reference voltage is exceeded,
the tip to ring voltage is calculated using Equation 4:
where:
V
TR
= Voltage differential between tip and ring.
R
L
= Loop resistance.
For on-hook transmission R
L
=
∞
, Equation 4 reduces to:
HC5523
V
TX
R
RX
R
DC1
R
DC2
C
DC
RSN
R
DC
I
RSN
TIP
RING
-2.5V
I
RING
I
TIP
A
2
I
TIP
I
RING
R
SG
R
SG
-5V
LOOP CURRENT
CIRCUIT
SATURATION GUARD
CIRCUIT
A
1
I
1
I
2
R
1
+
-
+
-
+
-
+
-
FIGURE 13. DC LOOP CURRENT
-5V
-5V
17.3k
0
1.2K
-50
-40
-30
-20
-10
0
V
BAT
= -48V, I
L
= 23mA, R
SG
= 4.0k
SATURATION
GUARD VOLTAGE
LOOP RESISTANCE (
)
FIGURE 14. V
TR
vs R
L
V
TIP
V
RING
RESISTIVE FEED
REGION
T
CONSTANT CURRENT
FEED REGION
SATURATION
GUARD VOLTAGE
∞
0
10
20
30
0
10
20
30
40
50
LOOP CURRENT (mA)
T
V
BAT
= -24V, R
SG
=
∞
V
BAT
= -48V, R
SG
= 4.0k
SATURATION GUARD
VOLTAGE, V
TR
= 38V
RESISTIVE FEED
REGION
CONSTANT CURRENT
FEED REGION
R
SG
= 4.0k
R
SG
=
∞
100k
100k
4k
1.5k
2k
700
<400
<1.2k
R
L
R
L
SATURATION GUARD
VOLTAGE, V
TR
= 13V
FIGURE 15. V
TR
vs I
L
and R
L
V
SGREF
12.5
5
--------------+
+
=
(EQ. 3)
V
TR
R
L
16.66
L
5
10
5
R
DC2
17300
+
(
)
+
R
DC1
+
----------------+
×
=
(EQ. 4)
V
TR
16.66
5
SG
--------------+
+
=
(EQ. 5)
HC5523
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