HC5513

FN3963 Rev.12.00

Page 13 of 20

August 2003

Ring Trip Detector

Ring trip detection is accomplished with the internal ring trip

comparator and the external circuitry shown in Figure 19. The

process of ring trip is initiated when the logic input pins are in the

following states: E0 = 0, E1 = 1/0, C1 = 1 and C2 = 0. This logic

condition connects the ring trip comparator to the DET output, and

causes the Ringrly pin to energize the ring relay. The ring relay

connects the tip and ring of the phone to the external circuitry in

Figure 19. When the phone is on-hook the DT pin is more positive

than the DR pin and the DET output is high. For off-hook

conditions DR is more positive than DT and DET goes low. When

DET goes low, indicating that the phone has gone off-hook, the

SLIC is commanded by the logic inputs to go into the active state.

In the active state, tip and ring are once again connected to the

phone and normal operation ensues.

Figure 19 illustrates battery backed unbalanced ring injected

ringing. For tip injected ringing just reverse the leads to the

phone. The ringing source could also be balanced.

NOTE: The DET output will toggle at 20Hz because the DT input is not

determine if the DET pin is low for more that half the time, if so the off-

hook condition is indicated.

Longitudinal Impedance

The feedback loop described in Figure 20(A, B) realizes the

desired longitudinal impedances from tip to ground and from

ring to ground. Nominal longitudinal impedance is resistive and

in the order of 22

.

In the presence of longitudinal currents this circuit attenuates

the voltages that would otherwise appear at the tip and ring

terminals, to levels well within the common mode range of the

SLIC. In fact, longitudinal currents may exceed the

programmed DC loop current without disturbing the SLIC’s VF

transmission capabilities.

The function of this circuit is to maintain the tip and ring

longitudinal currents. The differential transconductance

When a longitudinal current is injected onto the tip and ring

appears between the input terminals of the differential

to 500(

The circuit shown in Figure 20(B) illustrates the tip side of the

longitudinal network. The advantages of a differential input

current source are: improved noise since the noise due to

differential current gain and minimized offset error at the

Operational Amplifier inputs via the two 5k

 resistors.

Digital Logic Inputs

Table 1 is the logic truth table for the TTL compatible logic

input pins. The HC5513 has two enable inputs pins (E0, E1)

and two control inputs pins (C1, C2).

The enable pin E0 is used to enable or disable the DET output

pin. The DET pin is enabled if E0 is at a logic level 0 and

disabled if E0 is at a logic level 1.

The enable pin E1 gates the ground key detector to the DET

output with a logic level 0, and gates the loop or ring trip

detector to the DET output with a logic level 1.

A combination of the control pins C1 and C2 is used to select 1

of the 4 possible operating states. A description of each

operating state and the control logic follow:

Open Circuit State (C1 = 0, C2 = 0)

In this state the SLIC is effectively off. All detectors and both

the tip and ring line drive amplifiers are powered down,

presenting a high impedance to the line. Power dissipation is at

a minimum.

Active State (C1 = 0, C2 = 1)

The tip output is capable of sourcing loop current and for open

circuit conditions is about -4V from ground. The ring output is

capable of sinking loop current and for open circuit conditions is

current and ground key detectors are both active, E0 and E1

determine which detector is gated to the DET output.

Ringing State (C1 = 1, C2 = 0)

The ring relay driver and the ring trip detector are activated.

Both the tip and ring line drive amplifiers are powered down.

Both tip and ring are disconnected from the line via the

external ring relay.

Standby State (C1 = 1, C2 = 1)

Both the tip and ring line drive amplifiers are powered down.

Internal resistors are connected between tip to ground and ring to

TIP

RING

HC5513

DR

DT

RING TRIP

COMPARATOR

DET

RINGRLY

RING

RELAY

+

-

FIGURE 19. RING TRIP CIRCUIT FOR BATTERY BACKED RINGING