CPC7594 datasheet(12/20 Pages) IXYS

12 / 20 page

INTEGRATED CIRCUITS DIVISION

www.ixysic.com

R04

CPC7594

2. Functional Description

2.1 Introduction

2.1.1 CPC7594xA and CPC7594xB Logic States

• Talk. Break switches SW1 and SW2 closed, ringing

switches SW3 and SW4 open, and test switches

SW5 and SW6 open.

• Ringing. Break switches SW1 and SW2 open,

ringing switches SW3 and SW4 closed, and test

switches SW5 and SW6 open.

• Test. Break switches SW1 and SW2 open, ringing

switches SW3 and SW4 open, and channel test

switches SW5 and SW6 closed.

• All-off. Break switches SW1 and SW2 open, ringing

switches SW3 and SW4 open, and test switches

SW5 and SW6 open.

2.1.2 CPC7594xC Logic States

The CPC7594xC replaces the Test state with the

Test/Monitor state as defined below.

• Test/Monitor. Break switches SW1 and SW2

closed, ringing switches SW3 and SW4 open, and

test switches SW5 and SW6 closed.

The CPC7594 offers break-before-make and

make-before-break switching from the ringing state to

the talk state with simple TTL level logic input control.

Solid-state switch construction means no impulse

noise is generated when switching during ring

cadence or ring trip, eliminating the need for external

zero-cross switching circuitry. State control is via TTL

logic-level input so no additional driver circuitry is

required. The linear break switches SW1 and SW2

have exceptionally low RON and excellent matching

characteristics. The ringing switch, SW4, has a

minimum open contact breakdown voltage of 465 V at

+25

C sufficiently high with proper protection to

prevent breakdown in the presence of a transient fault

condition (i.e., passing the transient on to the ringing

generator).

Integrated into the CPC7594 is an over-voltage

clamping circuit, active current limiting, and a thermal

shutdown mechanism to provide protection for the

SLIC during a fault condition. Positive and negative

lightning surge currents are reduced by the current

limiting circuitry and hazardous potentials are diverted

away from the SLIC via the protection diode bridge or

the optional integrated protection SCR. Power-cross

potentials are also reduced by the current limiting and

thermal shutdown circuits.

To protect the CPC7594 from an over-voltage 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

maximum breakdown voltage of the switches. To

minimize the stress on the solid-state contacts, use of

a foldback or crowbar type secondary protector is

highly recommended. With proper selection of the

secondary protector, a line card using the CPC7594

will meet all relevant ITU, LSSGR, TIA/EIA and IEC

protection requirements.

The CPC7594 operates from a single +5 V supply.

This gives the device extremely low power

consumption in any state with virtually any range of

battery voltage. The battery voltage used by the

CPC7594 has a two fold function. It is used as a

reference and as a current source for the internal

integrated protection circuitry under surge conditions.

Second, it is used as a reference. In the event of

battery voltage loss, the CPC7594 enters the all-off

state.

2.2 Under Voltage Switch Lock Out Circuitry

2.2.1 Introduction

Smart logic in the CPC7594 now provides for switch

state control during both power up and power loss

transitions. An internal detector is used to evaluate the

VDD supply to determine when to de-assert the under

voltage switch lock out circuitry with a rising VDD and

when to assert the under voltage switch lock out

circuitry with a falling VDD. Any time unsatisfactory low

VDD conditions exist the lock out circuit overrides user

switch control by blocking the information at the

external input pins and conditioning internal switch

commands to the all off state. Upon restoration of VDD

the switches will remain in the all-off state until the

LATCH input is pulled low.

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