HC5504B Datasheet, PDF (6/9 Pages) Intersil Corporation – EIA/ITU PABX SLIC with 40mA Loop Feed

HC-5504B
Pin Descriptions (Continued)
24 PIN
SOIC
SYMBOL
DESCRIPTION
21
RX
Receive Input, 4-Wire Side - A high impedance analog input which is internally biased. Capacitive coupling to this
input is required. AC signals appearing at this input differentially drive the Tip feed and Ring feed terminals, which in
turn drive tip and ring through 300Ω of feed resistance on each side of the line.
22
C₄
Capacitor #4 - An external capacitor to be connected between this terminal and analog ground. This capacitor
prevents false ground key indication and false ring trip detection from occurring when longitudinal currents are
induced onto the subscriber loop from near by power lines and other noise sources. This capacitor is also required
for the proper operation of ring trip detection. Typical value is 0.5µF, to 1.0µF, 20V. This capacitor should be
nonpolarized.
23
AG
Analog Ground - To be connected to zero potential and serves as a reference for the transmit output (TX) and receive
(Note 5) input (RX) terminals.
24
TX
Transmit Output, 4-Wire Side - A low impedance analog output which represents the differential voltage across Tip
and Ring. Transhybrid balancing must be performed (using the SLIC microcircuit’s spare op amp) beyond this output
to completely implement two to four wire conversion. This output is unbalanced and referenced to analog ground.
Since the DC level of this output varies with loop current, capacitive coupling to the next stage is essential.
NC
No internal connection.
Functional Diagram
RS
RING SYNC
RC
RING COMMAND
RD
TIP
1/2 RING
TIP
RELAY _150Ω
150Ω
2 WIRE
TF
LOOP
V_B-
SECONDARY
PROTECTION
BG
V_B-
RF
1/2 RING
RELAY
RFS
150Ω
RING
RING
VOLTAGE
V_B-
150Ω
RING
PD
POWER DENIAL
RING
CONTROL
RING
TRIP
LOOP
MONITORING
DIFF
AMP
-
+
SHD _{SWITCH HOOK}
DETECTION
GKD _{GROUND KEY}
DETECTION
TX _TRANSMIT
OUTPUT
BATTERY
FEED
+1
LOOP
CURRENT
LIMITER
LINE
DRIVERS
-1
SLIC MICROCIRCUIT
+
-
OP
AMP
OUT
+IN
-IN
RX _RECEIVE
INPUT
6