HC55120_06 Datasheet, PDF (14/36 Pages) Intersil Corporation – Low Power Universal SLIC Family

HC55120, HC55121, HC55130, HC55140, HC55142, HC55143, HC55150
23. Four-Wire to Two-Wire Gain Tracking - The 4-wire to 2-wire
gain tracking is referenced to measurements taken for
E_RX = -10dBm, 1.0kHz signal, E_G source removed from circuit,
R_L = 600Ω and is computed using the following equation:
G_4-2 = 20 • log (V_TR/E_RX) vary amplitude -40dBm to +3dBm, or
-55dBm to -40dBm and compare to -10dBm reading.
V_TR, R_L and E_RX are defined in Figure 8. The level is specified at
the 4-wire receive port and referenced to a 600Ω impedance level.
24. Two-Wire Idle Channel Noise - The 2-wire idle channel noise
at V_TR is specified with the 2-wire port terminated in 600Ω (R_L)
and with the 4-wire receive port (VTX) floating (Reference
Figure 9).
25. Four-Wire Idle Channel Noise - The 4-wire idle channel noise
at V_TX is specified with the 2-wire port terminated in 600Ω (R_L).
The noise specification is with respect to a 600Ω impedance
level at V_TX. The 4-wire receive port (VTX) floating (Reference
Figure 9).
26. Harmonic Distortion (2-Wire to 4-Wire) - The harmonic
distortion is measured within the voice band with the following
conditions. E_G = 0dBm at 1kHz, R_L = 600Ω. Measurement
taken at V_TX. (Reference Figure 7).
27. Harmonic Distortion (4-Wire to 2-Wire) - The harmonic
distortion is measured within the voice band with the following
conditions. E_RX = 0dBm0. Vary frequency between 300Hz and
3.4kHz, R_L = 600Ω. Measurement taken at V_TR. (Reference
Figure 8).
28. Constant Loop Current - The constant loop current is
calculated using the following equation:
I_L = 1000/R_LIM = V_TR/600 (Reference Figure 10).
29. Ground Key Detector - (TRIGGER) Ground the Ring pin
through a 2.5kΩ resistor and verify that GKD goes low.
(RESET) Disconnect the Ring pin and verify that GKD goes
high.
(Hysteresis) Compare difference between trigger and reset.
30. Electrical Test - Not tested in production at -40°C.
Circuit Operation and Design Information
The UniSLIC14 family of SLICs are voltage feed current
sense Subscriber Line Interface Circuits (SLIC). For short
loop applications, the voltage between the tip and ring
terminals varies to maintain a constant loop current. For long
loop applications, the voltage between the tip and ring
terminals are relatively constant and the loop current varies
in proportion to the load.
The tip and ring voltages for various loop resistances are
shown in Figure 13. The tip voltage remains relatively
constant as the ring voltage moves to limit the loop current
for short loops.
The loop current for various loop resistances are shown in
Figure 14. For short loops, the loop current is limited to the
programmed current limit, set by RILIM. For long loop
applications, the loop current varies in accordance with
Ohms law for the given tip to ring voltage and the loop
resistance.
0
TIP
-5
-2.5V
-10
-15
RING
-20
-25
-30
-35
CONSTANT
-40 _{LOOP CURRENT}
-45 ^REGION
CONSTANT TIP TO RING
VOLTAGE REGION
VBH = -48V
RD = 41.2kΩ
ROH = 38.3kΩ
RDC_RAC = 19.6kΩ
RILim = 33.2kΩ
-44.5V
-50
200 600 1000 1400 1800 2000 4K 6K 8K 10K
LOOP RESISTANCE (Ω)
FIGURE 13. TIP AND RING VOLTAGES vs LOOP RESISTANCE
.
35
30
25
CONSTANT
20 LOOP CURRENT
REGION
15
CONSTANT TIP TO RING
VOLTAGE REGION
VBH = -48V
10
RD = 41.2kΩ
ROH = 38.3kΩ
RDC_RAC = 19.6kΩ
5
RILim = 33.2kΩ
0
200 600 1K 1.4K 1.8K 2.2K 2.6K 3.0K 3.4K 3.8K
LOOP RESISTANCE (Ω)
FIGURE 14. LOOP CURRENT vs LOOP RESISTANCE
The following discussion separates the SLIC’s operation into
its DC and AC paths, then follows up with additional circuit
and design information.
DC Feed Curve
The DC feed curve for the UniSLIC14 family is user
programmable. The user defines the on hook and off hook
overhead voltages (including the overhead voltage for off
hook pulse metering if applicable), the maximum and
minimum loop current limits, the switch hook detect
threshold and the battery voltage. From these requirements,
the DC feed curve is customized for optimum operation in
any given application. An Excel spread sheet to calculate the
external components can be downloaded off our web site
www.intersil.com/telecom/unislic14.xls.
14
FN4659.13
June 1, 2006