MC3456/MC3556 (CMOS) Dual Timer/Oscillator
Data sheet
Direct Replacement for NE556, LM556
by Tony van Roon

The MC3456/3556 silicon monolithic timing circuit are a highly stable controller capable of producing accurate time delays, or oscillation. In the time delay mode of operation, the time is precisely controlled by one external resistor and capacitor. For a stable operation as an oscillator, the free running frequency and the duty cycle are both accurately controlled with two external resistors and one capacitor. The circuit may be triggered and reset on falling waveforms, and the output structure can source or sink up to 200 mA or drive MTTL circuits.

mc4.jpg 22-Sec. solid-state time delay relay circuit
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  • Turn off time less than 2 micro seconds.block diagram
  • Maximum operating frequency greater than 500KHz.
  • Timing from microseconds to hours.
  • Operates in both astable and monostable modes.
  • High output current.
  • Adjustable duty-cycle.
  • TTL compatible.
  • Temperature stability of 0.005% per °C.
  • Rise and Fall times of output is 100nS typical.
  • Normally "on" or normally "off".
  • Output can also drive MTTL circuits.
  • Direct pin-compatible with the NE556/SE556/LM556 timers.
  • Dual version of the popular MC1455 timer.

    Some Applications:
  • Precision Timing.
  • Pulse generation.
  • Sequential timing.
  • Timedelay generation.
  • Pulse width modulation.
  • Pulse position modulation.
  • Missing Pulse Detector.

    Absolute Maximum Ratings:
  • Supply voltage for MC3456/MC3556 is +18 volt.
  • Discharge current (pin 7) is 200mA.
  • Power dissipation 680 milliWatts.
  • Operating temperature range for MC3456/MC3556 is 0 °C to +70 °C.
  • Storage temperature range from -65 to -150 °C.
  • Lead temperature (soldering, up to 60 sec) 300 °C.

  • The 'L' suffix stands for Ceramic package (mostly used in the Industry), case 632-08.
  • The 'D' suffix stands for Surface Mount, Plastic package, case 751-02 or SO-8.
  • The 'P' suffix stands for Plastic package, case 646-06.

  • Supply current when output high typically 1mA or less.
  • Tested at Vcc=5V and Vcc=15V.
  • This will determine the maximum value of Ra+Rb, for 15V operation, the max total
    R = 10 Mega-ohm, and for 5V operation, the max total of R = 3.4 Mega-ohm.
  • Specified with trigger input high.
  • Time measured from a positive going input pulse from 0 to 0.8 x Vcc into the threshold
    to the drop from high to low of the output. Trigger is tied to threshold.

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    Copyright © Tony van Roon