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8

CPC7582

Rev. 1.0

Functional Description

Introduction

The CPC7582 has four states:

closed, ringing switches SW3, SW4 open and loop

access switches SW5, SW6 open),

open, ringing switches SW3, SW4 closed and loop

access switches SW5, SW6 open)

open, ringing switches SW3, SW4 open and loop

access switches SW5, SW6 closed)

open, ringing switches SW3, SW4 open and loop

access switches SW5, SW6 open)

The CPC7582 offers break-before-make and make-

before-break switching with simple logic level input con-

trol. Solid state switch construction means no impulse

noise is generated when switching during ring cadence

or ring trip, thus eliminating the need for external “zero

cross” switching circuitry. State control is via logic level

input so no additional driver circuitry is required. The

line break switches SW1 and SW2 are linear switches

that have exceptionally low RDS

ON

and excellent

matching characteristics. The ringing access switch

SW4 has a breakdown voltage rating of >480V which is

sufficiently high, with proper protection, to prevent

breakdown in the presence of a transient fault condition

(i.e., passing the transient on to the ring generator).

Integrated into the CPC7582 is a diode bridge/SCR

clamping circuit, current limiting and thermal shut-

down mechanism to provide protection to the SLIC

device during a fault condition. Positive and negative

surges are reduced by the current limiting circuitry and

steered to ground via diodes and the integrated SCR.

Power cross transients are also reduced by the cur-

rent limiting and thermal shutdown circuits. Please

note that only the CPC7582BA has the integrated pro-

tection SCR.

To protect the CPC7582 from an overvoltage fault

condition, use of a secondary protector is required.

The secondary protector must limit the voltage seen at

the tip and ring terminals to a level below the max

breakdown voltage of the switches. To minimize the

stress on the solid-state contacts, use of a foldback or

crowbar type secondary protector is recommended.

With proper selection of the secondary protector, a

line card using the CPC7582 will meet all relevant

ITU, LSSGR, FCC or UL protection requirements.

The CPC7582 operates from a +5V supply only. This

gives the device extremely low idle and active power

dissipation and allows use with virtually any range of

battery voltage. A battery voltage is also used by the

CPC7582 as a reference for the integrated protection

circuit. In the event of a loss of battery voltage, the

CPC7582 will enter an “all off” state.

Switch Timing

The CPC7582 provides, when switching from the ring-

ing state to the idle/talk state, the ability to control the

timing when the ringing access switches SW3 and

SW4 are released relative to the state of the line break

switches SW1 and SW2 using simple logic level input.

This is referred to a “make before break” or “break

before make” operation. When the line break switch

contacts (SW1, SW2) are closed (or made) before the

ringing access switch contact (SW3, SW4) is opened

(or broken), this is referred to a ‘make-before-break’

operation. Break-before-make operation occurs when

the ringing access contact (SW3, SW4) is opened

(broken) before the line break switch contacts (SW1,

SW2) are closed (made). With the CPC7582 the

“make before break” and “break before make” opera-

tions can easily be selected by applying logic level

inputs to pins 9 and 10 (IN

device.

The logic sequences for either mode of operation are

given in Tables 6 and 7. Logic states and explanations

are given in Table 9.

Break-before make operation can also be achieved

using pin 7 (TSD) as an input. In table 7 lines 2 and 3

it is possible to induce the switches to “all off” by

grounding pin 7 (TSD) instead of apply logic input to

the pins. This has the effect of overriding the logic

inputs and forcing the device to the “all off” state. Hold

this input state for 25ms. During this hold period, tog-

gle the inputs from the ringing state (10) to the idle/talk

state (00). After the 25ms release pin 7 (TSD) to return

the switch control to the input pins 9 and 10 and reset

the device to the idle/talk state.

Setting TSD to +5V will allow switch control using the

logic pins 9 and 10. This setting, however, will also dis-

able the thermal shutdown circuit and is therefore not

recommended. When using logic controls via the input

pins 9 and 10, pin 7 (TSD) should be allowed to float.

As a result the two recommended states when using

pin 7 (TSD) as a control are 0 which forces the device

to the “all of state” or float which allows logic inputs to

pins 9 and 10 to remain active. This may require use

of an open collector buffer.