The smallest IttyBitty RC 555 timer oscillator

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Hello TechForum,

Today, I found the latest addition to the classic 555 timer in the form of the Microchip MIC1551YM5-TR. Thank you Petr Dvořák for sharing this idea (link below).

In the datasheet, they call it the “IttyBitty RC 555 Type Timer/Oscillator”. It is packaged in a SOT-23-5 package and operates with rail voltages as low as 2.7 VDC.

What is the difference between the MIC1551 and the MIC1553?

The classic 555 timer has eight pins while the MIC1551 and MIC1553 have five. Consequently, the smaller devices are somewhat limited in functionality. To mitigate this problem and to simplify the design, Microchip provides two variants as shown in Figure 1:

  • MIC1551: According to the datasheet: The MIC1551 can be used as an astable (oscillator) or monostable (one-shot) with separate threshold and trigger inputs. In the one-shot mode, the output pulse width is precisely controlled by an external resistor and a capacitor. Time delays may be accurately controlled from microseconds to hours. In the oscillator mode, the output is used to provide precise feedback, with a minimum of one resistor and one capacitor producing a 50% duty cycle square wave.

  • MIC1553: According to the datasheet, The MIC1553 is designed for astable (oscillator) operation only, with a chip select/reset (CS) input for low power shut-down. One resistor and one capacitor provide a 50% duty cycle square wave.

Figure 1: Typical application circuits for the MIC1551 and MIC1553 as seen in the device datasheet.
Figure 1: Typical application circuits for the MIC1551 and MIC1553 as seen in the device datasheet.1233×408 85.6 KB

Figure 1: Typical application circuits for the MIC1551 and MIC1553 as seen in the device datasheet.

Breadboarding with the Microchip MIC1551 and the MIC1553

If you would like to experiment with the new circuits, you could use an adapter board such as the Sparkfun 00717.

The 555 timer oscillator is a Jellybean component

The 555 timer is an honorary member of the Jellybean family. As defined in this canonical article, the Jellybean parts have several key characteristics including:

  • Multi-source production with competitive pricing: To classify as jellybean, at least 5 manufacturers offer the original or variants of the component. This results in competitive pricing and operates as a hedge against supply chain disruptions, ensuring a continued availability.

  • Legacy and Longevity: Jellybean components have stood the test of time, with continued production for at least 40 years.

  • High Stock levels at DigiKey: Since this is a DigiKey TechForum, post, we can be biased and set a threshold of 1,000,000 routinely stocked DigiKey components clause (inclusive of variants, marketplace, and complementary devices).

  • Education: The components are often included in kits and educational labs. The jellybean components are the building blocks of electronics education. Most jellybean components are referenced in the famous Horowitz and Hill “Art of Electronics” textbook - silver and gold.

Use of the MIC1551 and MIC1553 in education

The 555 has been used in education for decades as it provides a unique focal point for:

  • Digital circuits in the form of a flip flop
  • Voltage comparison with the 555’s resistor trio
  • Modes of operation e.g., one-shot vs astable multivibrator
  • RC time constants

The MIC1551 and MIC1553 extend this line of thinking with the inclusion of low voltage output drivers. Also, your students can explore the difference between the two ICs to better understand the operating modes of the 555 timer.

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Parting thoughts

I’ve always said every project needs a 555 timer. The MIC1551 and MIC1553 variant expand this idea and make it easier, especially when we consider the low external parts count when compared to a traditional 555.

Give it a try and let us know what you think.

Now what could we do with low power?

Sincerely,

Aaron

About this author

Aaron Dahlen, LCDR USCG (Ret.), serves as an application engineer at DigiKey. He has a unique electronics and automation foundation built over a 27-year military career as a technician and engineer which was further enhanced by 12 years of teaching (interwoven). With an MSEE degree from Minnesota State University, Mankato, Dahlen has taught in an ABET-accredited EE program, served as the program coordinator for an EET program, and taught component-level repair to military electronics technicians. Dahlen has returned to his Northern Minnesota home and thoroughly enjoys researching and writing articles such as this.

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