4047B datasheet(8/15 Pages) STMICROELECTRONICS

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VTR

t1 = – RC In

VDD +VTR

VDD –VTR

t2 = – RC In

2VDD –VTR

(VTR)(VDD –VTR)

tA =2 (t1 +t2) = –2 RC In

(VDD +VTR)(2 VDD –VTR)

ASTABLE MODE WAVEFORMS.

Typ : VTR = 0.5 VDD tA = 4.40 RC

Min : VTR = 0.33 VDD tA = 4.62 RC

Max : VTR = 0.67 VDD tA = 4.62 RC

thus if

tA = 4.40 RC

is used, the maximum vari-

ation will be (+ 5.0%, – 0.0%)

In addition to variations from unit-to-unit, the astable

period may vary as a function of frequency with re-

spect to VDD and temperature.

3 - MONOSTABLE MODE

The following analysis presents worst-case vari-

ations from unit-to-unit as a function of transfer-volt-

age (VTR) shift (33% – 67% VDD) for one-shot

(monostable) operation.

VTR

t1 = – RC In

2VDD

VDD –VTR

t2 = – RC In

2VDD –VTR

(VTR)(VDD –VTR)

tM =(t1 +t2)= – RC In

(2 VDD –VTR)(2 VDD)

MONOSTABLE WAVEFORMS.

Where tM = monostable mode pulse width. Values

for tM are as follows :

Typ : VTR = 0.5

VDD tM = 2.48 RC

Min : VTR = 0.33 VDD tM = 2.71 RC

Max : VTR = 0.67 VDD tM = 2.48 RC

Thus if

tM = 2.48 RC is used, the maximum vari-

ation will be (+ 9.3%, – 0.0%).

Note : In the astable mode, the first positive half

cycle has a duration of TM ; succeeding dur-

ations are tA/2.

In addition to variations from unit to unit, the mono-

stable pulse width may vary as a function of fre-

quency with respect to VDD and temperature.

4 - RETRIGGER MODE

The HCC/HCF4047B can be used in the retrigger

mode to extend the output-pulse duration, or to com-

pare the frequency of an input signal with that of the

internal oscillator. In the retrigger mode the input

pulse is applied to terminals 8 and 12, and the output

is taken from terminal 10 or 11. As shown in fig. A

normal monostable action is obtained when one re-

trigger pulse is applied. Extended pulse duration is

obtained when more than one pulse is applied. For

two input pulses, tRE =t1’+ t1 +2t2. For more than

two pulses, tRE (Q OUTPUT) terminates at some

variable time tD after the termination of the last re-

trigger pulse. tD is variable because tRE (Q OUT-

PUT) terminates after the second positive edge of

the oscillator output appears at flip-flop 4 (see logic

diagram).

HCC/HCF4047B

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