HCC4047B Datasheet, PDF (8/15 Pages) STMicroelectronics – LOW-POWELOW-POWER MONOSTABLE/ASTABLE MULTIVIBRATOR

HCC/HCF4047B
ASTABLE MODE WAVEFORMS.
t₁ = – RC In
V_TR
VDD + VTR
t₂ = – RC In
V_DD – V_TR
2 VDD – VTR
t_A
=
2
(t₁
+
t₂)
=
–2
RC
In
(VTR) (VDD – VTR)
(V_DD + V_TR) (2 V_DD – V_TR)
Typ : VTR = 0.5 VDD tA = 4.40 RC
Min : V_TR = 0.33 V_DD t_A = 4.62 RC
Max : V_TR = 0.67 V_DD t_A = 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
MONOSTABLE WAVEFORMS.
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.
t₁ = – RC In
V_TR
2 VDD
t₂ = – RC In
V_DD – V_TR
2 VDD – VTR
t_M = (t₁ + t₂) = – RC In
(VTR) (VDD – VTR)
(2 V_DD – V_TR) (2 V_DD)
Where t_M = monostable mode pulse width. Values
for tM are as follows :
Typ : VTR = 0.5 VDD tM = 2.48 RC
Min : V_TR = 0.33 V_DD t_M = 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, t_RE = 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. t_D is variable because t_RE (Q OUT-
PUT) terminates after the second positive edge of
the oscillator output appears at flip-flop 4 (see logic
diagram).
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