SN54AHCT123A, SN74AHCT123A

DUAL RETRIGGERABLE MONOSTABLE MULTIVIBRATORS

SCLS420G – JUNE 1998 – REVISED APRIL 2003

2

POST OFFICE BOX 655303

description/ordering information(continued)

Pulse triggering occurs at a particular voltage level and is not directly related to the transition time of the input

pulse. The A, B, and CLR inputs have Schmitt triggers with sufficient hysteresis to handle slow input transition

rates with jitter-free triggering at the outputs.

Once triggered, the basic pulse duration can be extended by retriggering the gated low-level-active (A) or

high-level-active (B) input. Pulse duration can be reduced by taking CLR low. CLR input can be used to override

A or B inputs. The input/output timing diagram illustrates pulse control by retriggering the inputs and early

clearing.

The variance in output pulse duration from device to device typically is less than

±0.5% for given external timing

components. An example of this distribution for the ’AHCT123A is shown in Figure 10. Variations in output pulse

duration versus supply voltage and temperature are shown in Figure 6.

During power up, Q outputs are in the low state, and Q outputs are in the high state. The outputs are glitch free,

without applying a reset pulse.

For additional application information on multivibrators, see the application report, Designing With the

SN74AHC123A and SN74AHCT123A, literature number SCLA014.

FUNCTION TABLE

(each multivibrator)

INPUTS

OUTPUTS

CLR

A

B

Q

Q

L

X

X

L

H

X

HX

L†

H†

X

XL

L†

H†

H

L

↑

H

#

H

↑

L

H

† These outputs are based on the

assumption

that

the

indicated

steady-state conditions at the A and

B inputs have been set up long enough to

complete any pulse started before the

setup.

logic diagram, each multivibrator (positive logic)

CLR

Cext

Rext/Cext

R

B

A

Q

Q