5
Pin Descriptions
24 PIN
SOIC SYMBOL DESCRIPTION
1 TIP An analog input connected to the TIP (more positive) side of the subscriber loop through a 150Ω feed resistor and a
ring relay contact. 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 through a 150Ω feed resistor and
a ring relay contact. 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 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.
4V
B
+ Positive Voltage Source - Most positive supply. V
B
+ is typically 12V or 5V.
5C
3
Capacitor #3 - 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 V
B
-. Typical value is 0.3µF, 30V.
6DG
(Note 5)
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 150Ω 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 150Ω feed resistor. Functions
with the TF terminal to provide loop current, feed voice signals to the telephone set, and sink longitudinal current.
11 V
B
- Negative Voltage Source - Most negative supply. V
B
- is typically -48V with an operational range of -42V to -58V.
Frequently referred to as “battery”.
12 BG
(Note 5)
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 10mA and disabled for loop currents less than 5mA.
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.
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.
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).
17 C
2
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 0.15µF, 10V. This capacitor is not used if
ground key function is not required and (Pin 17) may be left open or connected to digital ground.
18 OUT The analog output of the spare operational amplifier. The output voltage swing is typically ±5V.
19 -IN The inverting analog input of the spare operational amplifier.
20 +IN The non-inverting analog input of the spare operational amplifier.
HC-5504B
