55

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 re-

sistor and a ring relay contact. Functions with the Ring terminal to receive voice signals from the telephone

and for loop monitoring purposes.

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 telephone

and for loop monitoring purposes.

4

3

RFS

Senses ring side of loop for ground key and ring trip detection. During ringing, the ring signal is inserted

into the line at this node and RF is isolated from RFS via a relay.

54

65

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

76

DG

(Note 5)

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

puts on the SLIC microcircuit.

9

7

RS

Ring Synchronization Input - A TTL-compatible clock input. The clock should be arranged such that a pos-

itive pulse transition occurs on the zero crossing of the ring voltage source, as it appears at the RFS termi-

nal. For Tip side injected systems, the RS pulse should occur on the negative going zero crossing and for

Ring injected systems, on the positive going zero crossing. This ensures that the ring relay activates and

deactivates when the instantaneous ring voltage is near zero. If synchronization is not required, the pin

should be tied 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 signals to the telephone set, and sink

longitudinal current.

13

11

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

14

12

BG

(Note 5)

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 cur-

rents 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 cur-

rent 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 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

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 ca-

pacitor is not used if ground key function is not required and (Pin 17) may be left open or connected to digital

ground.

21

18

OUT

The analog output of the spare operational amplifier. The output voltage swing is typically

±5V.

23

19

-IN

The inverting analog input of the spare operational amplifier.

HC-5504B