4-6

Functional Diagram

26

22

Capacitor #4 - An external capacitor to be connected between this terminal and analog ground. This ca-

pacitor prevents false ground key indication and false ring trip detection from occurring when longitudinal

currents are induced onto the subscriber loop from nearby power lines and other noise sources. This ca-

pacitor is also required for the proper operation of ring trip detection. Typical value is 0.5

µF to 1.0µF, 20V.

This capacitor should be nonpolarized.

27

23

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

24

TX

Transmit Output, Four Wire Side - A low impedance analog output which represents the differential volt-

age 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 unbal-

anced and referenced to analog ground. Since the DC level of this output varies with loop current, capac-

itive coupling to the next stage is essential.

1, 8, 5, 22

NC

No Internal Connection.

NOTE:

to run separate grounds off a line card, the AG must be applied first.

Pin Descriptions

(Continued)

28 PIN

PLCC

24 PIN

DIP/SOIC

SYMBOL

DESCRIPTION

RING

RELAY

LOOP

CURRENT

LIMITER

BATTERY

FEED

+

DIFF

AMP

+

OP

AMP

LOOP

MONITORING

RING

CONTROL

2-WIRE

LOOP

SECONDARY

PROTECTION

+1

-1

LINE

DRIVERS

TIP

RING

PD

POWER DENIAL

150

Ω

RING

150

Ω

RF

BG

150

Ω

TF

TIP

RD

RC

RS

RING

VOLTAGE

RING SYNC

RING COMMAND

RING

TRIP

SHD

GKD

TX

TRANSMIT

OUTPUT

OUT

+IN

-IN

RX

RECEIVE

INPUT

SLIC MICROCIRCUIT

150

Ω

SWITCH HOOK

DETECTION

GROUND KEY

DETECTION

HC-5502B1