10

www.ixysic.com

R06

CPC7591

2. Functional Description

2.1 Introduction

The CPC7591 has three states:

ringing switches SW3 and SW4 open.

line break switches SW1 and SW2 open.

See “Truth Table” on page 9 for more information.

The CPC7591 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 ringing

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 line break switches SW1 and

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 CPC7591 is an over-voltage

clamping circuit, active current limiting, and a thermal

shutdown mechanism to provide protection to 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 CPC7591 from an overvoltage fault

condition, the use of a secondary protector is required.

The secondary protector must limit the voltage seen at

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 CPC7591

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

protection requirements.

The CPC7591 operates from a single +5 V supply

only. This gives the device extremely low idle and

active power consumption with virtually any range of

battery voltage. The battery voltage used by the

CPC7591 has a two fold function. For protection

purposes it is used as a fault condition current source

for the internal integrated protection circuitry.

Secondly, it is used as a reference so that in the event

of battery voltage loss, the CPC7591 will enter the

all-off state.

2.2 Under Voltage Switch Lock Out Circuitry

2.2.1 Introduction

Smart logic in the CPC7591 now provides for switch

state control during both power up and power loss

transitions. An internal detector is used to evaluate the

when to assert the under voltage switch lock out

switch control by blocking the information at the

external input pins and conditioning internal switch

commands to the all-off state. Upon restoration of

the LATCH input is pulled low.

internally set to ensure all internal logic is properly

biased and functional before accepting external switch

commands from the inputs to control the switch states.

assure proper logic and switch behavior up to the

moment the switches are forced off and external

inputs are suppressed.