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I am using TPL5010 http://www.ti.com/lit/ds/symlink/tpl5010.pdf watchdog timer's RSTn pulse to trigger 555 timer in monostable mode with 10 sec pulse width in order to turn ON relay using transistor at OUTPUT pin of 555 timer.

1. Here problem is that during startup TPL5010 generates tREXT = 100ms RST pulse which is triggering 555 timer and which will turn ON relay. How can I neglect this initial startup pulse to avoid triggering 555 timer during initial startup.

Both TPL5010 and 555 timer is running with 5V suply . I am thinking that if I can delay the supply voltage to 555 timer for a period till which TPL5010 finish it startup process.Is there any way I can solve this problem

All answers appreciate

enter image description here

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    \$\begingroup\$ Realistically this sounds like a poor solution even if it worked - whatever advantage you thought you were getting from the TLP5010 is likely negated by the ancient 555. You'd likely be better off with a low end MCU. \$\endgroup\$ – Chris Stratton Jul 30 '18 at 23:45
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    \$\begingroup\$ I suspect this is XY problem. Otherwise the description makes little sense. Can you explain what actual problem you are trying to solve? \$\endgroup\$ – Maple Jul 31 '18 at 0:23
  • \$\begingroup\$ tpl5010 watchdog IC is giving initial startup 100 ms RST pulse which I need to avoid to trigger the 555 timer . \$\endgroup\$ – ARYA1992 Jul 31 '18 at 1:09
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    \$\begingroup\$ @ARYA1992 That is a problem Y, which is created by your implementation. The problem X would be the desired functionality \$\endgroup\$ – Maple Jul 31 '18 at 6:04
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Allow me to explain why this is XY problem.

You've come with a solution Y to use RSTn signal to trigger 555 timer. This created a problem that you've asked to fix:

How can I neglect this initial startup pulse to avoid triggering 555 timer during initial startup?

The actual problem X, however, is:

"How do I trigger 555 timer periodically using TPL5010?".

Had you asked this question, the answer would have been: TPL5010 is designed to generate WAKE pulses periodically, and that is what you should be using, not RSTn. Note that in order for next WAKE to be generated, TPL needs DONE pulse coming in. In circuit without microcontroller you can use the output of your 555 timer to generate DONE.

Now, the funny thing is that your problem is not even XY problem, it is XY² problem. Because the real question should have been:

"How do I generate 10 sec pulse every N seconds?"

Then the answer would be completely different. First, the timers TPL5110 and TPL5111 are much better fit for this task. They do not require DONE signal to repeat the output pulse. Instead they wait almost to the end of programmed period and then toggle output back anyway. At the same time DONE can be used to de-assert output earlier. By looping back DRVn output to DONE input via RC delay circuit one can control the duration of the output pulse.

See, what I am getting at? There is no need in additional 555 timer. It all can be done with just a few parts. But you need to ask right question to get this answer. In the circuit below R1 sets the pulse period, R2 and C1 set the pulse duration.

enter image description here

BTW, you can try the same approach with TPL5010, by looping delayed WAKE pulse. Although I suspect it wouldn't work if the chip waits for first DONE to begin time interval.

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  • \$\begingroup\$ An "XY² problem" - I like it ;) \$\endgroup\$ – brhans Jul 31 '18 at 11:26

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