Nexperia
HEF4047B
Monostable/astable multivibrator
HEF4047B All information provided in this document is subject to legal disclaimers. © Nexperia B.V. 2017. All rights reserved.
Product data sheet Rev. 6 — 17 March 2017
14 / 22
11.2.1 Retrigger mode operation
The HEF4047B can be used in the retrigger mode to extend the output pulse duration.
It can also be used to compare the frequency of an input signal with the frequency of
the internal oscillator. In the retrigger mode, the input pulse is applied to pins 8 and 12,
and the output is taken from pin 10 or 11. Normal monostable action is obtained when
one retrigger pulse is applied (see Figure 10). Extended pulse duration is obtained when
more than one pulse is applied. For two input pulses, t
RE
= t
1
' + t
1
+ 2t
2
. For more than
two pulses, t
RE
(output O), terminates at some variable time, t
D
, after the termination of
the last retrigger pulse. t
D
is variable because t
RE
(output O) terminates after the second
positive edge of the oscillator output appears at flip-flop 4.
aaa-013289
OSCILLATOR
OUTPUT (pin 13)
+ TRIGGER;
RETRIGGER
(pins 8, 12)
O OUTPUT
(pin 10)
t
2
t
1
'
t
1
'
t
RE
t
RE
t
RE
t
1
t
2
t
2
t
D
Figure 10. Retrigger mode waveforms.
11.2.2 External counter option
The use of external counting circuitry extends time t
M
by any amount. Advantages
include digitally controlled pulse duration, small timing capacitors for long time periods,
and extremely fast recovery time. A typical implementation is shown in Figure 11.
The pulse duration at the output is:
(7)
Where t
ext
= pulse duration of the circuitry, and N is the number of counts used.
