HC5523IP datasheet(9/18 Pages) INTERSIL

9 / 18 page

The value of RSG should be calculated to allow maximum

loop length operation. This requires that the saturation guard

reference voltage be set as high as possible without clipping

the incoming or outgoing VF signal. A voltage margin of -4V

on tip and -4V on ring, for a total of -8V margin, is

recommended as a general guideline. The value of RSG is

calculated using Equation 6:

where:

VBAT = Battery voltage.

VMAR = Voltage Margin. Recommended value of -8V to

allow a maximum overload level of 3.1V peak.

For on-hook transmission RL = ∞, Equation 6 reduces to:

SLIC in the Standby Mode

Overall system power is saved by configuring the SLIC in the

standby state when not in use. In the standby state the tip and

ring amplifiers are disabled and internal resistors are connected

between tip to ground and ring to VBAT. This connection

enables a loop current to flow when the phone goes off-hook.

The loop current detector then detects this current and the

SLIC is configured in the active mode for voice transmission.

The loop current in standby state is calculated as follows:

where:

IL = Loop current in the standby state.

RL = Loop resistance.

VBAT = Battery voltage.

(AC) Transmission Path

SLIC in the Active Mode

Figure 16 shows a simpliﬁed AC transmission model. Circuit

analysis yields the following design equations:

where:

VTR = Is the AC metallic voltage between tip and ring,

including the voltage drop across the fuse resistors RF.

VTX = Is the AC metallic voltage. Either at the ground

referenced 4-wire side or the SLIC tip and ring terminals.

IM = Is the AC metallic current.

RF = Is a fuse resistor.

ZT = Is used to set the SLIC’s 2-wire impedance.

VRX = Is the analog ground referenced receive signal.

ZRX = Is used to set the 4-wire to 2-wire gain.

EG = Is the AC open circuit voltage.

ZL = Is the line impedance.

(AC) 2-Wire Impedance

The AC 2-wire impedance (ZTR) is the impedance looking

into the SLIC, including the fuse resistors, and is calculated

as follows:

Let VRX = 0. Then from Equation 10

510

•

BAT

MAR

–

()

DC1

DC2

()

600R

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







16.66V

–

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

17300

–







(EQ. 6)

510

•

BAT

MAR

16.66V

–

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

17300

–

(EQ. 7)

BAT

–

1800

Ω

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

≈

(EQ. 8)

•

(EQ. 9)

-----------

1000

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

(EQ. 10)

•

–

(EQ. 11)

VTX

RSN

TIP

RING

ZTR

VTR

VTX

1000

VTX

ZRX

HC5523

A = 4

VRX

A = 250

FIGURE 16. SIMPLIFIED AC TRANSMISSION CIRCUIT

1000

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

•

(EQ. 12)

HC5523

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