5

FN4539.3

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

using Equation 3.

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

Impedance Matching

The impedance of the device is programmed with the

the feedback amplifier that provides impedance matching. If

complex impedance matching is required, then a complex

RESISTIVE IMPEDANCE SYNTHESIS

in Equation 4.

The required impedance is defined by the terminating

impedance and protection resistors as shown in Equation 5.

ON HOOK POWER DISSIPATION

Forward or Reverse

BSEL = 0

-

44

60

mW

Forward or Reverse

BSEL = 1

-

90

150

mW

Low Power Standby

BSEL = 1

-

37

60

mW

OFF HOOK POWER DISSIPATION

Forward or Reverse

BSEL = 0

-

290

310

mW

POWER SUPPLY REJECTION RATIO

f = 300Hz

-

40

-

dB

f = 1kHz

-

35

-

dB

f = 3.4kHz

-

28

-

dB

f = 300Hz

-

45

-

dB

f = 1kHz

-

43

-

dB

f = 3.4kHz

-

33

-

dB

300Hz

≤ f ≤ 3.4kHz

-

30

-

dB

300Hz

≤ f ≤ 3.4kHz

-

35

-

dB

300Hz

≤ f ≤ 3.4kHz

-

33

-

dB

300Hz

≤ f ≤ 1kHz

-

40

-

dB

1kHz

< f ≤ 3.4kHz

-

45

-

dB

Electrical Specifications

current limit = 25mA. All AC Parameters are specified at 600

Ω 2-wire terminating impedance over the frequency

band of 300Hz to 3.4kHz. Protection resistors = 0

Ω. (Continued)

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNITS

⁄

=

(EQ. 1)

⁄

=

(EQ. 2)

1760

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

=

(EQ. 3)

()

=

(EQ. 4)

–

=

(EQ. 5)

HC5549