HC5513 Intersil Corporation, HC5513 Datasheet - Page 9

• Manufacturer Part Number: HC5513
• Description: TR909 DLC/FLC 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 <1.2k (R
21.4k ) 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
generates a current that is proportional to the tip to ring
voltage difference. I
until the tip to ring voltage exceeds 12.5V. When the tip to ring
voltage exceeds 12.5V (with no R
more current than I
amplifies its input current by a factor of 12 and the current
through R
current from A
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
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
V
V
R
R
SGREF
SG
TR
L
SGREF
TR
L
L
= Loop resistance.
50
40
30
20
10
0
= Voltage differential between tip and ring.
= Saturation Guard programming resistor.
=
0
100k
100k
R
RESISTIVE FEED
1
L
= Saturation Guard reference voltage.
=
1
decreases and the output voltage on R
becomes the difference between I
V
12.5
V
----------------------------------------------------------------------
R
REGION
BAT
BAT
L
2
16.66
+
. As the current from A
10
FIGURE 15. V
+
= -48V, R
= -24V, R
4k
1.5k
R
5 10
------------------
LOOP CURRENT (mA)
R
1
SG
DC1
1
+
SG
can sink. When this happens A
is internally set to sink all of A
5 10
pin provides the ability to increase the
5
+
SG
SG
R
20
DC2
= 21.4k
=
5
2k
700
62
TR
R
SG
vs I
600
SG
L
SG
30
resistor) A
2
AND R
<1.2k
<400
increases, the voltage
resistor value and the
CONSTANT CURRENT
FEED REGION
SATURATION GUARD
VOLTAGE, V
SATURATION GUARD
VOLTAGE, V
L
2
and the output
R
R
1
RSG
RSG
1
supplies
DC
. A
1
SG
’s current
2
= 21.4k
=
1
TR
TR
=
(EQ. 3)
(EQ. 4)
= 38V
= 13V
HC5513
For on-hook transmission R
V
The value of R
loop length operation. This requires that the saturation guard
reference voltage be set as high as possible without clipping
the incoming or outgoing VF signal. A voltage margin of -4V
on tip and -4V on ring, for a total of -8V margin, is
recommended as a general guideline. The value of R
calculated using Equation 6:
where:
V
V
overload level of 3.1V
For on-hook transmission, R
R
SLIC in the Standby Mode
Overall system power is saved by configuring the SLIC in the
standby state when not in use. In the standby state the tip
and ring amplifiers are disabled and internal resistors are
connected between tip to ground and ring to V
connection enables a loop current to flow when the phone
goes off-hook. The loop current detector then detects this
current and the SLIC is configured in the active mode for
voice transmission. The loop current in standby state is
calculated as follows:
where:
I
R
V
(AC) Transmission Path
SLIC in the Active Mode
Figure 16 shows a simplified AC transmission model. Circuit
analysis yields the following design equations:
I
V
V
---------- -
V
R
L
L
Z
TR
BAT
MARGIN
SG
BAT
L
TR
TR
TX
SG
= Loop current in the standby state.
T
= Loop resistance.
------------------------------- -
R
V
+
=
=
=
=
=
L
= Battery voltage.
= Battery voltage.
BAT
V
-----------
Z
16.66
------------------------------------------------------------------------------------------------------------------------------------------------- -
+
V
E
----------------------------------------------------------------------------
RX
RX
V
V
1800
TX
G
BAT
BAT
= Recommended value of -8V to allow a maximum
–
–
=
+
I
3V
+
M
I
------------ -
1000
M
–
5 10
------------------
–
SG
I
R
M
V
V
Z
SG
MARGIN
5 10
2R
MARGIN
L
should be calculated to allow maximum
5
F
PEAK
5
–
16.66V
.
L
L
5 10
1
= , Equation 4 reduces to:
= , Equation 6 reduces to:
+
------------------------------------------ -
R
5
DC1
600R
+
R
L
DC2
BAT
–
16.66V
. This
(EQ. 10)
(EQ. 11)
SG
(EQ. 5)
(EQ. 6)
(EQ. 7)
(EQ. 8)
(EQ. 9)
is