SCAN ABT Live Insertion and Power Cycling Characteristics

SCAN ABT is intended to serve in Live Insertion backplane

that while external circuitry to control the output enable pin

is unnecessary there may be a need to implement differen-

well pre-bias circuitry for backplane pins may be necessary

to avoid capacitive loading effects during live insertion

SCAN ABT provides control of output enable pins during

power cycling via the circuit in

Figure A It essentially con-

During

range all internal device circuitry is inactive leaving output

and IO pins of the device in high impedance From approxi-

(POR) in

Figure A becomes active and maintains device

high impedance mode The POR does this by providing a

low from its output that resets the flip-flop The output Q of

the flip-flop then goes high and disables the NOR gate from

POR circuitry becomes inactive and ceases to control the

input must receive an inactive-to-active transition a high-to-

flip-flop With a low on the Q output of the flip-flop the NOR

During

power-down the Power-On-Reset circuitry will be-

come active and reset the flip-flop at approximately 18V

device will then remain in high impedance for the remaining

Some suggestions to help the designer with live insertion

issues

Reset circuitry becomes inactive

er-On-Reset has become active

The description of the functionality of the Power-On-Reset

circuitry can best be described in the diagram of

Figure B

TLF11657 – 19

FIGURE A

TLF11657 – 20

FIGURE B

SCAN ABT includes additional power-on reset circuitry not otherwise included in ABT devices

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