TC74VHC123,221AF/AFT/AFK

2012-02-29

6

Functional Description

(1)

Standby state

comparators that relate to the timing of the output pulse, and two reference voltage supplies turn off.

The total supply current is only leakage current.

(2)

Trigger operation

Trigger operation is effective in any of the following three cases. First, the condition where the

A

input is low, and the B input has a rising signal; second, where the B input is high, and the A input

has a falling signal; and third, where the A input is low and the B input is high, and the CLR

input has a rising signal.

Upon triggering, output Q becomes high, following some delay time of the internal F/F and gates. It

IC returns to its MONOSTABLE state.

(3)

Retrigger operation (TC74VHC123A)

When a new trigger is applied to either input A or B while in the MONOSTABLE state, it is

If the new trigger is very close to previous trigger, such as an occurrence during the discharge cycle,

it will have no effect.

The minimum time for a trigger to be effective 2nd trigger, trr (min.), depends on VCC and CX.

(4)

Reset operation

In normal operation, the CLR input is held high. If CLR is low, a trigger has no effect because

This means if CLR is set low, the IC goes into a wait state.