The ‘123 is a dual retriggerable monostable multivibrator with output pulse width control by three methods. The basic pulse time is programmed by selection of external resistance (R_ext) and capacitance (C_ext) values. Once triggered, the basic pulse width may be extended by retriggering the gated active LOW going edge input (A) or the active HIGH going edge input (B), or be reduced by use of the overriding active LOW reset.

The basic output pulse width is essentially determined by the values of external capacitance and timing resistance.

For pulse widths when C_ext ≤ 1000pF, see Figure A.

When C_ext > 1000pF, the output pulse width is defined as:

t_w = 0.28 R_ext · C_ext (1 + 0.7/R_ext)

The external resistance and capacitance are normally connected as shown in Figure B. If an electrolytic capacitor is to be used with an inverse voltage rating of less than 1V then Figure C should be used. (Inverse voltage rating of an electrolytic is normally specified at 5% of the forward voltage rating.) If the inverse voltage rating is 1V or more (this includes a 100% safety margin) then Figure B can be used. Note that if Figure C is used the timing equations change as follows:

t_w ≅ 0.25 R_ext · C_ext (1 + 0.7/R_ext)

 Datasheet

Manufactured: 1980 week 2

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