Here is my feasibility report. The scenario is, I have been asked to find a suitable replacement for the LM555 timer microchips our company has been using  in our products because the company that produce these chips are discontinuing them. A LM555 timer is a chip that can be used to send out different clock pulses. When you see on a computer that it says the processor runs at 2.6 giga-Hertz it is something similar to an LM555 that is sending out a 2.6 giga-Hertz signal to keep all the other components running together and in sync.

 

 

LM555 Timer Replacement Feasibility Report

By: Adam Kincaid

4/30/2016

 

  The purpose of this report is to find a suitable replacement for the LM555 timers we are currently  using. Finding a replacement is a necessity due to the manufacturer discontinuing their 555 timer line of products. I will be comparing 3 possible replacements in this report. They are Texas Instrument’s LM555 (TI), Fairchild’s LM555 (F) and National Semiconductors LM555 (NS). I have narrowed it down to these 3 possibilities by looking at the chips we get from all manufacturers and comparing how often those manufacturers chips fail in the field. I will be comparing them on the criteria of rise and fall times, supply voltage, and supply current.

  The rise and fall times refer to how quickly the timer can turn its output high and how quickly it can turn its output low. The rise times are TI 100ns (nano seconds), F 100ns, and NS 100ns. The fall times are TI 100ns, F 100ns, NS 100ns. It is not surprising that all of these are exactly the same. These values were collected off of data sheets and those listed only the typical values for these categories. Since this chip has a specific purpose they would want to convey that it should be able to switch from high to low and low to high in the window we would expect from a rival chip.

  Supply voltage is the amount of voltage the chip needs supplied to it in order to operate as well as the maximum it can handle. The values I got for this category was a range of voltages. The supply voltages are TI 4.5-16V (Volts), F 4.5-16V, and NS 4.5-16V. This range is fairly typical for a chip like this 4.5V is the lower side of a digital electronics high signal and 16V is the upper side of what most integrated circuits can handle. This is a good sign that we shouldn’t have to adjust the supply voltage from what it is in our current application most likely.

  Supply current is the current that the chip needs supplied to it to run as well as the maximum it can handle. The data sheets have 2 entries for this category one for a 5V supply and one for a 15V supply, we are going to work off of the 5V supply data since it is closer to the voltage in most applications. The data I gathered was TI 3mA (milli-Amps) typically to 6mA maximum, F 3mA typically to 6mA maximum, and NS 3mA typically to 6mA maximum. Like the supply current this is a pretty typical range for electronics of a digital nature which is where you would expect to see a chip such as this.

 

Comparative Table	Texas Instruments	Fairchild	National Semiconductor
Rise/Fall Time	100ns/100ns	100ns/100ns	100ns/100ns
Supply Voltage	4.5V min-16V max	4.5V min-16V max	4.5V min-16V max
Supply Current	3mA typical-6mA max	3mA typical-6mA max	3mA typical-6mA max

 

   Due to my 3 criteria having exactly the same data for all 3 chips I cannot make an accurate recommendation on which one would be best. The categories that are on the data sheets that I didn’t cover here are also exactly the same or there is negligible difference between them. Without knowing the specifications of the chip it should be able to replace as well as the information on how we have it integrated I can’t use the negligible differences as determining factors. I would recommend that we acquire 10 of each chip for each application we have them in that is unique in how it is integrated and start conducting tests to see how each one does in that specific application. After he have gathered that data we can make a more informed decision about which LM555 we should go with.

 

 

I will admit the conclusion I came to is a little underwhelming however, that is the way these things go in my field. a LM555 is a very specific chip that won’t vary much if at all from one manufacturer to another on paper. the only way to really tell a difference is to test them. I do also recognize that I stretched the definition of a feasibility report a little however, to do it properly for my field I would have to do something like, compare the cost and results of using an operational amplifier integrated circuit, and an operational amplifier made of discrete transistors, and mimicking an operational amplifier in firmware or other non physical means. This would have been really interesting to do but would have taken more than the time allotted for this project and I would have to come up with some very specific requirements of the tests so that they would be comparable in theory.