CPC7593ZCTR datasheet(16/24 Pages) IXYS

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INTEGRATED CIRCUITS DIVISION

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R05

CPC7593

The rising VDD switch lock-out release threshold is

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.

For a falling VDD event, the lock-out threshold is set to

assure proper logic and switch behavior up to the

moment the switches are forced off and external

inputs are suppressed.

To facilitate hot plug insertion and system power up

state control, the LATCH pin has an integrated weak

pull up resistor to the VDD power rail that will hold a

non-driven LATCH pin at a logic high state. This

enables board designers to use the CPC7593 with

FPGAs and other devices that provide high

impedance outputs during power up and logic

configuration. The weak pull up allows a fan out of up

to 32 when the system’s LATCH control driver has a

logic low minimum sink capability of 4mA.

2.2.2 Hot Plug and Power Up Circuit Design

Considerations

There are six possible start up scenarios that can

occur during power up. They are:

All inputs defined at power up & LATCH = 0

All inputs defined at power up & LATCH = 1

All inputs defined at power up & LATCH = Z

All inputs not defined at power up & LATCH = 0

All inputs not defined at power up & LATCH = 1

All inputs not defined at power up & LATCH = Z

Under all of the start up situations listed above the

CPC7593 will hold all of it’s switches in the all-off state

during power up. When VDD requirements have been

satisfied the LCAS will complete it’s start up procedure

in one of three conditions.

For start up scenario 1 the CPC7593 will transition

from the all-off state to the state defined by the inputs

when VDD is valid.

For start up scenarios 2, 3, 5, and 6 the CPC7593 will

power up in the all-off state and remain there until the

LATCH pin is pulled low. This allows for an indefinite

all-off state for boards inserted into a powered system

but are not configured for service or boards that need

to wait for other devices to be configured first.

Start up scenario 4 will start up with all switches in the

all-off state but upon the acceptance of a valid VDD the

LCAS will revert to any one of the legitimate states

listed in the truth tables and there after may randomly

change states based on input pin leakage currents

and loading. Because the LCAS state after power up

can not be predicted with this start up condition it

should never be utilized.

On designs that do not wish to individually control the

LATCH pins of multi-port cards it is possible to bus

many (or all) of the LATCH pins together to create a

single board level input enable control.

2.3 Switch Logic

2.3.1 Start-up

The CPC7593 uses smart logic to monitor the VDD

supply. Any time the VDD is below an internally set

threshold, the smart logic places the control logic to

the all-off state. An internal pullup on the LATCH pin

locks the CPC7593 in the all-off state following

start-up until the LATCH pin is pulled down to a logic

low. Prior to the assertion of a logic low at the LATCH

pin, the switch control inputs must be properly

conditioned.

2.3.2 Switch Timing

The CPC7593 provides, when switching from the

ringing state to the talk state, the ability to control the

release timing of the ringing switches SW3 and SW4

relative to the state of the break switches SW1 and

SW2 using simple TTL logic-level inputs. The two

available techniques are referred to as

make-before-break and break-before-make operation.

When the switch contacts of SW1 and SW2 are closed

(made) before the ringing switch contacts of SW3 and

SW4 are opened (broken), this is referred to as

make-before-break operation. Break-before-make

operation occurs when the ringing contacts of SW3

and SW4 are opened (broken) before the switch

contacts of SW1 and SW2 are closed (made). With

the CPC7593, make-before-break and

break-before-make operations can easily be

accomplished by applying the proper sequence of

logic-level inputs to the device.

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