HC5503

FN4344 Rev 5.00

Page 12 of 17

June 2004

Pin Descriptions

24 PIN

SOIC

SYMBOL

DESCRIPTION

1

TIP

An analog input connected to the TIP (more positive) side of the subscriber loop. Functions with the Ring terminal to

receive voice signals from the telephone and for loop monitoring purposes.

2

RING

An analog input connected to the RING (more negative) side of the subscriber loop. Functions with the Tip terminal to

receive voice signals from the telephone and for loop monitoring purposes.

3

RFS

Senses ring side of loop for 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.

4VCC

Positive Voltage Source - Most positive supply. VCC is typically 5V.

5C1

Capacitor #1 - An external capacitor to be connected between this terminal and analog ground. Required for proper operation

of the loop current limiting function, and for filtering VBAT. Typical value is 0.3F, 16V.

6

DG

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

SLIC microcircuit.

7

RS

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

transition occurs on the zero crossing of the ring voltage source, as it appears at the RFS terminal. 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.

8RD

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

9

TF

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

 feed resistor. Functions with

the RF terminal to provide loop current, feed voice signals to the telephone set, and sink longitudinal current.

10

RF

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

 feed resistor. Functions

with the TF terminal to provide loop current, feed voice signals to the telephone set, and sink longitudinal current.

11

VBAT

Negative Voltage Source - Most negative supply. VBAT is typically -24V. Frequently referred to as “battery”.

12

BG

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

terminal.

13

SHD

Switch Hook Detection - A low active LS TTL - compatible logic output. This output is enabled for loop currents

exceeding 10.5mA and disabled for loop currents less than 5mA.

15

PD

Power Denial - A low active TTL - Compatible logic input. When enabled, the switch hook detect (SHD) is not

necessarily valid, and the relay driver (RD) output is disabled.

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).

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 deferentially drive the Tip feed and Ring feed terminals, which in turn drive tip

and ring through 150

 of feed resistance on each side of the line.

22

C2

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

false ring trip detection from occurring when longitudinal currents are induced onto the subscriber loop from nearby

power lines and other noise sources. Recommended value is 1.0

F, 20V. This capacitor should be nonpolarized.

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.

24

TX

Transmit Output, Four Wire Side - A low impedance analog output which represents the differential voltage across Tip and

Ring. 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.

14

NC

Used during production testing. For proper operation of the SLIC, this pin should float.

17, 18, 19,

20

NC

No internal connection.

NOTE: All grounds (AG, BG, and DG) must be applied before VCC or VBAT. Failure to do so may result in premature failure of the part. If a user

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