4-5

Pin Descriptions

28 PIN

PLCC

24 PIN

DIP/SOIC

SYMBOL

DESCRIPTION

2

1

TIP

An analog input connected to the TIP (more positive) side of the subscriber loop through a 150

Ω feed

resistor and a ring relay contact. Functions with the Ring terminal to receive voice signals from the tele-

phone and for loop monitoring process.

3

2

RING

An analog input connected to the RING (more negative) side of the subscriber loop through a 150

Ω feed

resistor and a ring relay contact. Functions with the Tip terminal to receive voice signals from the tele-

phone and for loop monitoring purposes.

43

54

Capacitor #1 - Optional Capacitor used to improve power supply rejection. This pin should be left open if un-

used.

65

Capacitor #3 - An external capacitor to be connected between this terminal and analog ground. Required

30V.

7

6

DG

Digital Ground - To be connected to zero potential and serves as a reference for all digital inputs and out-

puts on the SLIC.

9

7

RS

Ring Synchronization Input - A TTL - Compatible Clock Input. The clock should be arranged such that a

positive transition occurs on the negative going zero crossing of the ring voltage source, ensuring that the

ring relay is activated and deactivated when the instantaneous ring voltage is near zero. If synchronization

is not required, tie to 5V.

10

8

RD

Relay Driver - A low active open collector logic output. When enabled, the external ring relay is energized.

11

9

TF

Tip Feed - A low impedance analog output connected to the TIP terminal through a 150

Ω feed resistor.

Functions with the RF terminal to provide loop current, feed voice signals to the telephone set, and sink

longitudinal current.

12

10

RF

Ring Feed - A low impedance analog output connected to the RING terminal through a 150

Ω feed resistor.

Functions with the TF terminal to provide loop current, feed voice signal to the telephone set, and sink

longitudinal current.

13

11

to -58V. Frequently referred to as “battery”.

14

12

BG

Battery Ground - To be connected to zero potential. All loop current and some quiescent current flows into

this ground terminal.

16

13

SHD

Switch Hook Detection - A Low Active LS TTL - Compatible Logic Output. This output is enabled for loop

currents exceeding 10mA and disabled for loop currents less than 5mA.

17

14

GKD

Ground Key Detection - A Low Active LS TTL - Compatible Logic Output. This output is enabled if the DC

current into the ring lead exceeds the DC current out of the tip lead by more than 20mA, and disabled if

this current difference is less than 10mA.

18

15

PD

Power Denial - A Low Active TTL - Compatible Logic Input. When enabled the switch hook detect (SHD)

and ground key detect (GKD) are 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 rising edge 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

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

false ground key indications from occurring during ring trip detection. Typical value is 0.15

µF, 10V. This

capacitor is not used if ground key function is not required.

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 cou-

pling 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.

HC-5502B1