TLC555: PCN change due to factory transfer

Hi Conor 

i am in the same situation, i need to have some consideration about the change in electrical consideration.

I have tested a 2023 batch and a 2025 batch (so the one which accomodate the PCN), i have found some behaviour discrepancy between the two batches (i'm using the components as oscillator).

So anyone have some justification about that?

Conner, 

Post PCN material should be similar but a little faster. Shorter prop delays and faster edges. 

Marco,

For 20kHz , I would expect no change. 

Ron,

i have tested the post PCN components and there is some change in the behaviour with the same configuration.

The components is a little bit faster and so we need to change the final product in which it is installed,

i have reviewed the datasheet revision J (and compare it vith revision I) but i do not understand the reason why. 

I think it is something related to the timing charactheristics but i have not saw any differences apart from the absence , in revision J, of the data for the initial error.

Do you have some suggestion for this variation?

.

Hi Ron,

As far as the following updated part of the data sheet is concerned, there is no mention of shorter prop delays or faster edges.
・Changes from Revision I (July 2019) to Revision J (November 2023)

We need to be aware of the potential issues that may be causing problems in our application, including the comments made by Marco. Please give us more details.

Thanks,

Conor

Marco, Connor

Marco, do you have frequency distribution chart? TLC555 is a general purpose timer, some variance is to be expected.  I still expect no distribution change for 19.2kHz with PCN. 

Connor, please describe the issue and provide values and or waveforms. 

PCN is a major change [design, process]. It would be impossible for it to be exactly the same. Erroring toward slightly faster is a lesser offense. In data sheet it is the limits that are major. With both pre and post PCN in play, it is too soon to consider a typical value change. At a future date typical may be replaced.  

It is possible that you only have pre PCN devices; the issue may not be PCN related. Please provide device marking or label information. 

Hi Ron,

up to now we have made two sampling:

- with "old" TLC555 we have found 19280 Hz (unfortunately we have only 1 sample)

- with "new" revision of TLC555 we have found:

         -Sample 1 20208Hz

         -Sample 2 20304Hz

         -Sample 3 20160Hz

         -Sample 4 20224Hz

         -Sample 5 20272Hz

         -Sample 6 20216Hz

         -Sample 7 20224Hz

         -Sample 8 20192Hz

         -Sample 9 20080Hz

         -Sample 10 20240Hz

with the same configuration seems to be more or less 5% faster.

Marco

Marco,

I put your values and data sheet topical's into my astable excel calculator. Nominal frequency is 20.784kHz. A perfect 555 timer would be 20.818kHz

If everything was working to make slowest and fastest (cap at 10%) the minimum would be 18.7kHz and maximum 23.36kHz

If you would like to play with the calculator. I think your previous caps were bigger, perhaps closer to 240pF

not19p2kHz.xlsx 

So you mean that this issue depends on the production variability of the batch of the TLC555 and up to now we are lucky to find components that works in the lower part of the min-max calculated frequency range? thank you to share your file we have somenting similar.

Marco,

TLC555 variability is a factor at high frequency or very low timing capacitance. In all usage cases, timing capacitor variance is a big factor. In all formulas (including mime) the timing "C" value includes all sources of capacitance. This would be the sum of the timing cap choice, the board parasitic capacitance, the TLC pin 2,6 capacitance. For the last one, typical in data sheet is 2.1pF per pin, so 4.2pF; that's a 2% bump to the 220pF cap choice. 

I still think caps play the biggest role. Can you compare the actual capacitance value for the fastest and slowest boards?