HC-5504B1_03 Datasheet, PDF (6/10 Pages) Intersil Corporation – ITU Low Cost, PABX SLIC With 40mA Loop Feed

HC-5504B1
Pin Descriptions (Continued)
28 PIN
PLCC SYMBOL
DESCRIPTION
26
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.
27
AG Analog Ground - To be connected to zero potential and serves as a reference for the transmit output (TX) and receive
input (RX) terminals.
28
TX Transmit Output, Four 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.
1, 8,
15, 22
NC No internal connection.
NOTE: All grounds (AG, BG, and DG) must be applied before V_B+ or V_B-. Failure to do so may result in premature failure of the part. If a user wishes
to run separate grounds off a line card, the AG must be applied first.
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
LOOP
CURRENT
LIMITER
+1
LINE
DRIVERS
-1
SLIC MICROCIRCUIT
+
OP
AMP
OUT
+IN
-IN
RX _RECEIVE
INPUT
6