HC5513 Просмотр технического описания (PDF) - Renesas Electronics
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HC5513 Datasheet PDF : 20 Pages
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HC5513
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 (RSG = 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.
50
VBAT = -48V, RSG = 21.4k
40
30
CONSTANT CURRENT
FEED REGION
SATURATION GUARD
VOLTAGE, VTR = 38V
20
VBAT = -24V, RSG =
10 RESISTIVE FEED
REGION
00
10
20
30
LOOP CURRENT (mA)
SATURATION GUARD
VOLTAGE, VTR = 13V
RL 100k
RL 100k
4k
1.5k
2k
700
<1.2k RRSG = 21.4k
<400 RRSG =
FIGURE 15. VTR vs IL AND RL
The Saturation Guard circuit (Figure 13) monitors the tip to ring
voltage via the transconductance amplifier A1. A1 generates a
current that is proportional to the tip to ring voltage difference. I1
is internally set to sink all of A1’s current until the tip to ring
voltage exceeds 12.5V. When the tip to ring voltage exceeds
12.5V (with no RSG resistor) A1 supplies more current than I1
can sink. When this happens A2 amplifies its input current by a
factor of 12 and the current through R1 becomes the difference
between I2 and the output current from A2. As the current from
A2 increases, the voltage across R1 decreases and the output
voltage on RDC decreases. This results in a corresponding
decrease in the loop current. The RSG pin provides the ability to
increase the saturation guard reference voltage beyond 12.5V.
Equation 3 gives the relationship between the RSG resistor
value and the programmable saturation guard reference
voltage:
VSGREF
=
12.5
+
-5---------1---0----5-
RSG
(EQ. 3)
where:
VSGREF = Saturation Guard reference voltage.
RSG = Saturation Guard programming resistor.
When the Saturation guard reference voltage is exceeded, the
tip to ring voltage is calculated using Equation 4:
VTR = RL R-----L---1--+-6---.--6-R--6--D---+--C---5-1----+----1-R--0---D-5---C----R2----S----G-6----0---0--
where:
(EQ. 4)
VTR = Voltage differential between tip and ring.
RL = Loop resistance.
FN3963 Rev.12.00
August 2003
For on-hook transmission RL = , Equation 4 reduces to:
VTR
=
16.66
+
-5---------1---0----5-
RSG
(EQ. 5)
The value of RSG should be calculated to allow maximum 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 RSG is calculated using
Equation 6:
RSG=
----------------------------------------------------------------5---------1----0---5-----------------------------------------------------------------
VBAT
–
VMARGI
N
1
+
---R-----D----C-6---10----0+----R-R---L--D----C----2----
– 16.66V
(EQ. 6)
where:
VBAT = Battery voltage.
VMARGIN = Recommended value of -8V to allow a maximum
overload level of 3.1VPEAK.
For on-hook transmission, RL = , Equation 6 reduces to:
RSG = --V----B----A----T------–-----V----M5-----A----R-1---G0----5I--N-----–-----1---6----.-6----6---V---
(EQ. 7)
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 VBAT. This 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:
IL R--V---L-B----+A----T1----8--–-0---0-3----V--
(EQ. 8)
where:
IL = Loop current in the standby state.
RL = Loop resistance.
VBAT = Battery voltage.
(AC) Transmission Path
SLIC in the Active Mode
Figure 16 shows a simplified AC transmission model. Circuit
analysis yields the following design equations:
VTR = VTX + IM 2RF
(EQ. 9)
V-----T---X-- + -V----R----X-- = ----I--M------
ZT ZRX 1000
VTR = EG – IM ZL
(EQ. 10)
(EQ. 11)
Page 9 of 20
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