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
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6 Functional description
The HEF4047B consists of a gate-able astable multivibrator incorporating logic
techniques to permit positive or negative edge-triggered monostable multivibrator action
with retriggering and external counting options.
Inputs include +TRIGGER, −TRIGGER, ASTABLE, ASTABLE, RETRIGGER and MR
(master reset). Buffered outputs are O, O and OSCILLATOR OUTPUT. In all modes of
operation an external capacitor (C
t
) must be connected between CTC and RCTC, and an
external resistor (R
t
) must be connected between RTC and RCTC.
A HIGH level on the ASTABLE input enables astable operation. The period of the square
wave at O and O outputs is a function of the external components employed. ‘True’ input
pulses on the ASTABLE or ‘complement’ pulses on the ASTABLE input, allow the circuit
to be used as a gate-able multivibrator. The OSCILLATOR OUTPUT period is half of
the O output in the astable mode. However, a 50% duty factor is not guaranteed at this
output.
In the monostable mode, positive edge-triggering is accomplished by applying a leading-
edge pulse to the +TRIGGER input and a LOW level to the −TRIGGER input. For
negative edge-triggering, a trailing-edge pulse is applied to the −TRIGGER and a HIGH
level to the +TRIGGER. Input pulses may be of any duration relative to the output pulse.
The multivibrator can be retriggered (on the leading-edge only) by applying a common
pulse to both the RETRIGGER and +TRIGGER inputs. In this mode, the output pulse
remains HIGH as long as the input pulse period is shorter than the period determined by
the RC components.
An external count down option implements coupling O to an external ‘N’ counter and
resetting the counter with the trigger pulse. The counter output pulse is fed back to the
ASTABLE input and has a duration equal to N times the period of the multivibrator. A
HIGH level on the MR input assures no output pulse during an ON-power condition. This
input can also be activated to terminate the output pulse at any time. In the monostable
mode, a HIGH level or power-ON reset pulse must be applied to MR, whenever V
DD
is
applied.
