CPC7581

R05

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11

2.2.1 Make-Before-Break Operation Logic Table (Ringing to Talk Transition)

To use break-before-make ringing switch release

operational sequence shown in “Break-Before-Make

Operation Logic Table (Ringing to Talk Transition)” on

page 11 to occur.

2.2.2 Break-Before-Make Operation Logic Table (Ringing to Talk Transition)

Logic states and explanations are given in “Truth Table”

on page 9.

2.3 Data Latch

The CPC7581 has an integrated data latch. The latch

operation is controlled by logic-level input pin 11

(LATCH). The data input of the latch is pin 10

internal node used for state control. When the LATCH

control pin is at logic 0, the data latch is transparent

and data control signals flow directly through to state

control. A change in input will be reflected in a change

is switch state. When the LATCH control pin is at logic

1, the data latch is active and a change in input control

will not affect switch state. The switches will remain in

the position they were in when the LATCH changed

from logic 0 to logic 1 and will not respond to changes

override state control.

The thermal shutdown mechanism activates when the

device die temperature reaches a minimum of 110° C,

placing the device in the all-off state regardless of

logic input. During thermal shutdown mode, pin 8

If presented with a short duration transient such as a

lightning event, the thermal shutdown feature will

typically not activate. But in an extended power-cross

event, the device temperature will rise and the thermal

shutdown will activate forcing the switches to the all-off

state. At this point the current measured through the

break switches (SW1 and SW2) will drop to zero.

Once the device enters thermal shutdown it will

remain in the all-off state until the temperature of the

device drops below the de-activation level of the

thermal shutdown circuit. This permits the device to

State

Latch

Timing

Break

Switches

Ringing

Return

Switch

(SW3)

Ringing

Switch

(SW4)

Ringing

1

0Z

-Off

On

On

Make-

Before-

Break

0

SW4 waiting for next zero-current crossing to

turn off. Maximum time is one-half of the ringing

cycle. In this transition state, current that is

limited to the dc break switch current limit value

will be sourced from the ring node of the SLIC.

On

Off

On

Talk

0

Zero-cross current has occurred

On

Off

Off

State

Latch

Timing

Break

Switches

Ringing

Return

Switch

(SW3)

Ringing

Switch

(SW4)

Ringing

1

0

Z-

Off

On

On

All-off

1

0

Hold this state for one-half of the ringing cycle.

SW4 waiting for zero current to turn off.

Off

Off

On

All-off

1

Zero current has occurred. SW4 has opened

Off

Off

Off

Talk

0

Z

Release break switches

On

Off

Off