The HEF4047B consists of a gatable 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 (Ct) must be connected between CTC and RCTC, and an external resistor (Rt) 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 gatable 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 VDD is applied.
Features and benefits
■ Monostable (one-shot) or astable (free-running) operation
■ True and complemented buffered outputs
■ Only one external resistor and capacitor required
■ Positive- or negative-edge triggering
■ Output pulse width independent of trigger pulse duration
■ Retriggerable option for pulse-width expansion
■ Long pulse width possible using small RC components with external counter provision
■ Fast recovery time independent of pulse width
■ Pulse-width accuracy maintained at duty cycles approaching 100%
■ Free-running or gatable operating modes
■ 50% duty cycle
■ Oscillator output available