HC5526IP datasheet(10/18 Pages) INTERSIL

10 / 18 page

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 ZL = 600Ω.

The value of ZB = 18.7kΩ.

VTX

RSN

TIP

RING

ZTR

VTR

VTX

1000

VTX

ZRX

HC5526

A = 4

VRX

A = 250

FIGURE 16. SIMPLIFIED AC TRANSMISSION CIRCUIT

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)

HC5526

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