52

Functional Diagram

24

20

+IN

The non-inverting analog input of the spare operational amplifier.

25

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 amplifiers, which in turn drive tip and ring through 300

Ω of feed resistance on each

side of the line.

26

22

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 lon-

gitudinal currents are induced onto the subscriber loop from nearby power lines and other noise

sources. This capacitor 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

(Note 5)

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, 4-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 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, 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

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

+

-

+1

+

-

HC-5502B