HC55183, HC55184

FN4519 Rev 8.00

Page 8 of 19

August 10, 2010

Design Equations

Loop Supervision Thresholds

SWITCH HOOK DETECT

The switch hook detect threshold is set by a single external

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

current and the peak off hook current while still ringing.

response time.

Loop Current Limit

The loop current limit of the device is programmed by the

Equation 3.

limit programming range is from 15mA to 45mA.

Impedance Matching

The impedance of the device is programmed with the external

amplifier that provides impedance matching. If complex

impedance matching is required, then a complex network can

RESISTIVE IMPEDANCE SYNTHESIS

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

When the device source impedance and protection resistors

equals the terminating impedance, the receive gain equals

unity.

2-WIRE TO 4-WIRE GAIN

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

When the protection resistors are set to zero, the transhybrid

gain is -6dB.

COMPLEX IMPEDANCE SYNTHESIS

complex programming network provides complex impedance

synthesis.

The reference designators in the programming network match

synthesis. The design equations for each component are

provided in the following.



=

(EQ. 1)



=

(EQ. 2)

1760

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

=

(EQ. 3)



=

(EQ. 4)

–

=

(EQ. 5)

2

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







–

=

(EQ. 6)

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







–

=

(EQ. 7)

++

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







–

=

(EQ. 8)

FIGURE 1. COMPLEX PROGRAMMING NETWORK

2-WIRE

NETWORK

PROGRAMMING

NETWORK

400



–





=

(EQ. 9)



=

(EQ. 10)



=

(EQ. 11)