CPC7691

R01

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2. Functional Description

2.1 Introduction

The CPC7691 has three states:

ringing switches SW3 and SW4 open.

line break switches SW1 and SW2 open.

See “Truth Table” on page 8 for more information.

The CPC7691 offers both break-before-make and

make-before-break switching techniques when

transitioning 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

thereby eliminating the need for external zero-cross

switching circuitry. State-control input is via TTL logic

levels so no additional driver circuitry is required. The

linear line break switches, SW1 and SW2, have

characteristics. SW4, the ringing switch, has a

minimum open contact breakdown voltage of 465V at

+25

C and a minimum dv/dt immunity of 1500v/us,

sufficiently high to prevent breakdown in the presence

of a transient fault condition (i.e., prevent passing the

transient on to the ringing generator).

Integrated into the CPC7691 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 CPC7691 from an over-voltage 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 CPC7691

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

protection requirements.

The CPC7691 operates from a single +5V supply

giving the device extremely low power consumption

with virtually any range of battery voltage. The battery

voltage used by the CPC7691 has a twofold function.

First, for protection purposes, it is used as a current

source during fault conditions by the integrated

internal protection circuitry. Second, it is used as a

reference so that in the event of battery voltage loss,

the CPC7691 will enter the All-Off state.

2.2 Start-up

Voltage Lock Out (UVLO) threshold, the smart logic

places the switch control logic into the All-Off state. An

internal pull-up at the LATCH pin holds the CPC7691

in the All-Off state until the LATCH pin is pulled down

properly conditioned prior to the assertion of a logic

low at the LATCH pin.

2.3 Data Latch

The CPC7691 has an integrated transparent data

latch. Latch enable operation is controlled by the

application of TTL logic input levels at the LATCH pin.

the data latch output is an internal node used for state

control. When the LATCH enable control pin is at

logic 0, the data latch is transparent, and the

to the state control circuitry. With LATCH = 0, a change

Whenever LATCH = 1, the data latch is active and

not result in a change to the control logic or affect the

existing state.