hc5523 Intersil Corporation, hc5523 Datasheet - Page 9

• Manufacturer Part Number: hc5523
• Description: Lssgr/tr57 Co/loop Carrier Slic With Low Power Standby
• Manufacturer: Intersil Corporation

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 <1.2kΩ
(R
feed region and for resistances >1.2kΩ 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.
R
R
SG
L
L
50
40
30
20
10
-10
-20
-30
-40
-50
0
0
= 4.0k
0
100kΩ
100kΩ
0
RESISTIVE FEED
CONSTANT CURRENT
GUARD VOLTAGE
GUARD VOLTAGE
V
V
Ω
REGION
BAT
BAT
FEED REGION
) the SLIC is operating in the constant current
SATURATION
SATURATION
10
FIGURE 15. V
= -48V, R
= -24V, R
4kΩ
1.5kΩ
LOOP CURRENT (mA)
FIGURE 14. V
I
RING
I
LOOP RESISTANCE (Ω)
TIP
SG
SG
V
BAT
RING
20
= 4.0kΩ
=
TIP
2kΩ
700Ω
∞
1.2K
TR
= -48V, I
9
vs I
TR
RESISTIVE FEED
vs R
L
L
30
HC5523
and R
<1.2kΩ
<400Ω
= 23mA, R
REGION
L
CONSTANT CURRENT
FEED REGION
SATURATION GUARD
VOLTAGE, V
SATURATION GUARD
VOLTAGE, V
L
I
TIP
R
R
+
+
SG
-
-
SG
SG
I
RING
FIGURE 13. DC LOOP CURRENT
= 4.0kΩ
= 4.0kΩ
=
∞
TR
TR
Ω
∞
= 38V
= 13V
V
V
TIP
RING
A
SATURATION GUARD
HC5523
1
I
1
LOOP CURRENT
-5V
CIRCUIT
CIRCUIT
The Saturation Guard circuit (Figure 13) monitors the tip to
ring voltage via the transconductance amplifier A
generates a current that is proportional to the tip to ring
voltage difference. I
current until the tip to ring voltage exceeds 12.5V. When the
tip to ring voltage exceeds 12.5V (with no R
supplies more current than I
A
through R
output current from A
voltage across R
decreases. This results in a corresponding decrease in the
loop current. The R
saturation guard reference voltage beyond 12.5V. Equation
3 gives the relationship between the R
the programmable saturation guard reference voltage:
where:
V
R
When the Saturation guard reference voltage is exceeded,
the tip to ring voltage is calculated using Equation 4:
where:
V
R
For on-hook transmission R
V
V
V
2
SGREF
TR
SGREF
SG
L
TR
TR
A
amplifies its input current by a factor of 12 and the current
= Loop resistance.
2
I
2
= Voltage differential between tip and ring.
= Saturation Guard programming resistor.
=
=
-5V
R
16.66
L
=
= Saturation Guard reference voltage.
1
×
12.5
becomes the difference between I
16.66
------------------------------------------------------------------------------------
+
I
R
---------------------------------- -
R
RSN
+
L
SG
1
---------------------------------- -
R
+
5 10
+
decreases and the output voltage on R
R
SG
SG
(
•
5 10
+
1
R
1
5 10
+
-
2
•
17300
is internally set to sink all of A
DC1
•
+
. As the current from A
-
+
pin provides the ability to increase the
5
17.3kΩ
17300
5
5
+
⁄
(
R
L
R
1
DC2
SG
= ∞, Equation 4 reduces to:
can sink. When this happens
+
) 600
V
RSN
R
-2.5V
R
⁄
17300
TX
DC
SG
SG
-5V
)
R
resistor value and
SG
SG
2
R
R
R
2
RX
DC1
DC2
increases, the
resistor) A
and the
1
. A
1
’s
1
C
DC
(EQ. 3)
(EQ. 4)
(EQ. 5)
DC
1