HC5523 Datasheet, PDF (9/18 Pages) Intersil Corporation – LSSGR/TR57 CO/Loop Carrier SLIC with Low Power Standby

HC5523
I_M
TIP
R_F
Z_L
V_TR
+
-
Z_TR
+
E_G
-
+
V_TX
-
I_M
RING ^RF
A = 250
+_-
1
A = 250
A=4
HC5523
FIGURE 16. SIMPLIFIED AC TRANSMISSION CIRCUIT
V_TX
+
V_TX
Z_T
-
RSN
I_M
1000
Z_RX
+
V_RX
-
The value of R_SG 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 R_SG is
calculated using Equation 6:


RSG=






--------------------------------------------------------------⁵-----^•----¹---⁰----⁵---------------------------------------------------------------
( VBAT
–
VMAR)
×

1

+
(_---R_{----D-----C--6---1-0---0-+---R--}R_{--L--D-----C-----2----})
– 16.66V
–


17300



(EQ. 6)
where:
V_BAT = Battery voltage.
V_MAR = Voltage Margin. Recommended value of -8V to
allow a maximum overload level of 3.1V peak.
For on-hook transmission R_L = ∞, Equation 6 reduces to:
R_SG = --_V----_B----_A----_T------–----⁵-_V----_M^•----¹-_A---⁰-_R--⁵---–-----₁---₆---_.--₆---₆----_V--- – 17300
(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 V_BAT. 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:
I_L ≈ -_R-^V---_L-^B----+^A----^T₁----₈--–-₀---₀-³---_Ω-^V--
(EQ. 8)
where:
I_L = Loop current in the standby state.
R_L = Loop resistance.
V_BAT = 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:
V_TR = V_TX + I_M • 2R_F
(EQ. 9)
V_{---Z--T--T-X-- + -}VZ_{----RR----XX-- = 1----0I--M-0----0-}
V_TR = E_G – I_M • Z_L
(EQ. 10)
(EQ. 11)
where:
V_TR = Is the AC metallic voltage between tip and ring,
including the voltage drop across the fuse resistors R_F.
V_TX = Is the AC metallic voltage. Either at the ground
referenced 4-wire side or the SLIC tip and ring terminals.
I_M = Is the AC metallic current.
R_F = Is a fuse resistor.
Z_T = Is used to set the SLIC’s 2-wire impedance.
V_RX = Is the analog ground referenced receive signal.
Z_RX = Is used to set the 4-wire to 2-wire gain.
E_G = Is the AC open circuit voltage.
Z_L = Is the line impedance.
(AC) 2-Wire Impedance
The AC 2-wire impedance (Z_TR) is the impedance looking
into the SLIC, including the fuse resistors, and is calculated
as follows:
Let V_RX = 0. Then from Equation 10
V_TX
=
Z_T
•
----^I--^M------
1000
(EQ. 12)
64