HC55183ECMZ datasheet(9/21 Pages) INTERSIL

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Design Equations

Loop Supervision Thresholds

SWITCH HOOK DETECT

The switch hook detect threshold is set by a single external

resistor, RSH. Equation 1 is used to calculate the value of RSH.

The term ISH is the desired DC loop current threshold. The

loop current threshold programming range is from 5mA to

15mA.

GROUND KEY DETECT

The ground key detector senses a DC current imbalance

between the Tip and Ring terminals when the ring terminal is

connected to ground. The ground key detect threshold is not

externally programmable and is internally fixed to 12mA

regardless of the switch hook threshold.

RING TRIP DETECT

The ring trip detect threshold is set by a single external

resistor, RRT. IRT should be set between the peak ringing

current and the peak off hook current while still ringing.

The capacitor CRT, in parallel with RRT, will set the ring trip

response time.

Loop Current Limit

The loop current limit of the device is programmed by the

external resistor RIL. The value of RIL can be calculated

using Equation 3.

The term ILIM is the desired loop current limit. The loop

current limit programming range is from 15mA to 45mA.

Impedance Matching

The impedance of the device is programmed with the

external component RS. RS is the gain setting resistor for

the feedback amplifier that provides impedance matching. If

complex impedance matching is required, then a complex

network can be substituted for RS.

RESISTIVE IMPEDANCE SYNTHESIS

The source impedance of the device, ZO , can be calculated

in Equation 4.

The required impedance is defined by the terminating

impedance and protection resistors as shown in Equation 5.

4-WIRE TO 2-WIRE GAIN

The 4-wire to 2-wire gain is defined as the receive gain. It is

a function of the terminating impedance, synthesized

impedance and protection resistors. Equation 6 calculates

the receive gain, G42.

When the device source impedance and protection resistors

equals the terminating impedance, the receive gain equals

unity.

2-WIRE TO 4-WIRE GAIN

The 2-wire to 4-wire gain (G24) is the gain from tip and ring to

the VTX output. The transmit gain is calculated in Equation 7.

When the protection resistors are set to zero, the transmit

gain is -6dB.

TRANSHYBRID GAIN

The transhybrid gain is defined as the 4-wire to 4-wire gain

(G44).

When the protection resistors are set to zero, the transhybrid

gain is -6dB.

COMPLEX IMPEDANCE SYNTHESIS

Substituting the impedance programming resistor, RS, with a

complex programming network provides complex

impedance synthesis.

The reference designators in the programming network

match the evaluation board. The component RS has a

different design equation than the RS used for resistive

impedance synthesis. The design equations for each

component are provided below.

600 I

⁄

(EQ. 1)

1800 I

⁄

(EQ. 2)

1760

LIM

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

(EQ. 3)

400 Z

()

(EQ. 4)

–

(EQ. 5)

O + 2 RP + ZL

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







–

(EQ. 6)

O + 2RP + ZL

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







–

(EQ. 7)

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







–

(EQ. 8)

FIGURE 1. COMPLEX PROGRAMMING NETWORK

2-WIRE

NETWORK

PROGRAMMING

NETWORK

400

()

–

()

(EQ. 9)

400

(EQ. 10)

2 400

⁄

(EQ. 11)

HC55180, HC55181, HC55183, HC55184

HC55183ECMZ Datasheet(PDF) 9 Page - Intersil Corporation

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