CPC7591

R06

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2.4 Data Latch

The CPC7591 has an integrated transparent data

latch. The latch enable operation is controlled by TTL

logic input levels at the LATCH pin. Data input to the

the data latch are internal nodes used for state control.

When the LATCH enable control pin is at logic 0 the

control signal flows directly through the data latch to

will be reflected by a change in switch state.

Whenever the LATCH enable control pin is at logic 1,

the data latch is active and data is locked. Subsequent

the control logic or affect the existing switch state.

The switches will remain in the state they were in

when the LATCH pin changes from logic 0 to logic 1

and will not respond to changes in input as long as the

the latch function. Since internal thermal shutdown

control and external “All-off” control is not affected by

state control.

internal pull-up current source with a nominal value of

16

A biased from V

As an output, this pin indicates the status of the

thermal shutdown circuitry. Typically, during normal

fault conditions that create excess thermal loading the

CPC7591 will enter thermal shutdown and a logic low

will be output.

CPC7591 into the “All-Off” state by simply pulling the

input low. For applications using low-voltage logic

recommends the use of an open-collector or an

normal operation when the all-off state is not required.

An open-collector or open-drain type device is

recommended to drive this pin.

2.6 Ringing Switch Zero-Cross Current Turn Off

After the application of a logic input to turn SW4 off,

the ringing switch is designed to delay the change in

state until the next zero-crossing. Once on, the switch

requires a zero-current cross to turn off, and therefore

should not be used to switch a pure DC signal. The

switch will remain in the on state no matter the logic

input until the next zero crossing. These switching

characteristics will reduce and possibly eliminate

overall system impulse noise normally associated with

ringing switches. See IXYS IC Division’s application

note AN-144, Impulse Noise Benefits of Line Card Access

Switches for more information. The attributes of ringing

switch SW4 may make it possible to eliminate the

need for a zero-cross switching scheme. A minimum

impedance of 300

 in series with the ringing

generator is recommended.

2.7 Power Supplies

Both a +5 V supply and battery voltage are connected

to the CPC7591. Switch state control is powered

exclusively by the +5 V supply. As a result, the

CPC7591 exhibits extremely low power consumption

during active and idle states.

Although battery power is not used for switch control, it

is required to supply trigger current for the integrated

internal protection circuitry SCR during fault

conditions. This integrated SCR is designed to

Because the battery supply at this pin is required to

source trigger current during negative overvoltage

fault conditions at tip and ring, it is important that the

net supplying this current be a low impedance path for

high speed transients such as lightning. This will

permit trigger currents to flow enabling the SCR to

activate and thereby prevent a fault induced negative

2.8 Battery Voltage Monitor

battery voltage. If system battery voltage is lost, the

CPC7591 immediately enters the all-off state. It

remains in this state until the battery voltage is

restored. The device also enters the all-off state if the

system battery voltage goes more positive than –10 V,