HC5513 datasheet(13/18 Pages) INTERSIL

13 / 18 page

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

voltages symmetrically around VBAT/2, in the presence of

longitudinal currents. The differential transconductance

ampliﬁers GT and GR accomplish this by sourcing or sinking

the required current to maintain VC at VBAT/2.

When a longitudinal current is injected onto the tip and ring

inputs, the voltage at VC moves from it’s equilibrium value

VBAT/2. When VC changes by the amount ∆VC, this change

appears between the input terminals of the differential

transconductance ampliﬁers GT and GR. The output of GT

and GR are the differential currents ∆I1 and ∆I2, which in

turn feed the differential inputs of current sources IT and IR

respectively. IT and IR have current gains of 250 single

ended and 500 differentially, thus leading to a change in IT

and IR that is equal to 500(∆I) and 500(∆I2).

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 current source 2IO is now correlated, power savings due

to differential current gain and minimized offset error at the

Operational Ampliﬁer inputs via the two 5k

Ω 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 about VBAT + 4V. VF signal transmission is

normal. The loop 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 VBAT to allow loop current detect in an off-hook condition.

The loop current and ground key detectors are both active, E0

and E1 determine which detector is gated to the DET output.

AC Transmission Circuit Stability

To ensure stability of the AC transmission feedback loop two

compensation capacitors CTC and CRC are required.

Figure 21 (Application Circuit) illustrates their use.

Recommended value is 2200pF.

FIGURE 20A.

FIGURE 20B.

FIGURE 20. LONGITUDINAL IMPEDANCE NETWORK

TIP

RING

VBAT/2

∆I1

∆I2

RLARGE

∆VT

ILONG

HC5513

ILONG

∆VR

VBAT/2

RLARGE

TIP

RING

Ω

2I0

∆I1

TIP CURRENT SOURCE

WITH DIFFERENTIAL INPUTS

TIP DIFFERENTIAL

TRANSCONDUCTANCE

AMPLIFIER

HC5513

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