5

Functional Diagram

18

15

PD

Power Denial - A low active TTL - Compatible logic input. When enabled, the ring feed voltage collapses to

the tip feed voltage (~4V). The DC feed is disabled, but the AC transmission is maintained. The switch hook

detect (SHD) is not necessarily valid, and the relay driver (RD) output is disabled.

19

16

RC

Ring Command - A low active TTL - Compatible logic input. When enabled, the relay driver (RD) output goes

low on the next high level of the ring sync (RS) input, as long as the SLIC is not in the power denial state

(PD = 0) or the subscriber is not already off- hook (SHD = 0).

20

17

NC

Leave disconnected.

21

18

OUT

The analog output of the spare operational amplifier.

23

19

-IN

The inverting analog input of the spare operational amplifier.

24

20

+IN

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

25

21

RX

Receive Input, Four 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.

26

22

Capacitor #2 - An external capacitor to be connected between this terminal and analog ground. This

capacitor is required for the proper operation of ring trip detection. Recommended value 0.82

µF ±10% 10V

non-polarized.

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 proportional to the loop current.

Transhybrid balancing must be performed 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.

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

28 PIN

PLCC

24 PIN

DIP/SOIC

SYMBOL

DESCRIPTION

+

DIFF

AMP

+

OP

AMP

LOOP

MONITORING

RING

CONTROL

2-WIRE

LOOP

SECONDARY

PROTECTION

LINE

DRIVERS

TIP

RING

PD

POWER DENIAL

RING

RF

BG

TF

TIP

RD

RC

RS

RING SYNC

RING COMMAND

RING

TRIP

SHD

TX

TRANSMIT

OUTPUT

OUT

+IN

-IN

RX

RECEIVE

INPUT

SLIC MICROCIRCUIT

1/2 RING

RELAY

RING

VOLTAGE

RFS

1/2 RING

RELAY

SWITCH HOOK

DETECTION

-1

+1

BATTERY

FEED

LOOP

CURRENT

LIMITER

HC5503PRC