HC5523IP datasheet(10/18 Pages) INTERSIL

10 / 18 page

ZTR is deﬁned as:

Substituting in Equation 9 for VTR

Substituting in Equation 12 for VTX

Therefore

Equation 16 can now be used to match the SLIC’s

impedance to any known line impedance (ZTR).

Example:

Calculate ZT to make ZTR = 600Ω in series with 2.16µF.

RF =20Ω.

ZT = 560kΩ in series with 2.16nF

(AC) 2-Wire to 4-Wire Gain

The 2-wire to 4-wire gain is equal to VTX/ VTR

From Equations 9 and 10 with VRX = 0

(AC) 4-Wire to 2-Wire Gain

The 4-wire to 2-wire gain is equal to VTR/VRX

From Equations 9, 10 and 11 with EG = 0

For applications where the 2-wire impedance (ZTR,

Equation 15) is chosen to equal the line impedance (ZL), the

expression for A4-2 simpliﬁes to:

(AC) 4-Wire to 4-Wire Gain

The 4-wire to 4-wire gain is equal to VTX/VRX

From Equations 9, 10 and 11 with EG = 0

Transhybrid Circuit

The purpose of the transhybrid circuit is to remove the

receive signal (VRX) from the transmit signal (VTX), thereby

preventing an echo on the transmit side. This is

accomplished by using an external op amp (usually part of

the CODEC) and by the inversion of the signal from the

4-wire receive port (RSN) to the 4-wire transmit port (VTX).

Figure 17 shows the transhybrid circuit. The input signal will

be subtracted from the output signal if I1 equals I2. Node

analysis yields the following equation:

The value of ZB is then

Where VRX/VTX equals 1/ A4-4

Therefore

Example:

Given: RTX = 20kΩ, ZRX = 280kΩ, ZT = 562kΩ (standard

value), RF = 20Ω and Z = 600Ω

The value of ZB = 18.7kΩ

Supervisory Functions

The loop current, ground key and the ring trip detector

outputs are multiplexed to a single logic output pin called

DET. See Table 1 to determine the active detector for a given

logic input. For further discussion of the logic circuitry see

section titled “Digital Logic Inputs”.

-----------

(EQ. 13)

-----------

•

-----------------------

(EQ. 14)

1000

-------------

(EQ. 15)

1000

–

()

•

(EQ. 16)

1000

600

ω 2.16

•

–

•

-----------------------------------------

220

•

–





•

–

-----------

T 1000

⁄

T 1000

⁄

------------------------------------------

(EQ. 17)

–

-----------

–

1000

-------------

--------------------------------------------

•

(EQ. 18)

–

-----------

–

---

•

(EQ. 19)

–

-----------

–

1000

-------------

--------------------------------------------

•

(EQ. 20)

-----------

(EQ. 21)

–

-----------

•

(EQ. 22)

-----------

•

1000

-------------

--------------------------------------------

•

(EQ. 23)

HC5523

VTX

RSN

RTX

RFB

CODEC/

FILTER

VTX

ZRX

VRX

FIGURE 17. TRANSHYBRID CIRCUIT

HC5523

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