I noticed that the 7705 is also designed to perform a reset on voltage loss scenarios (probably obvious to you all) is it worth checking the VCC on pin 8 and 7 to see if its dropping in time with the pulses?
only other thing I can see is the cap on REF is too small, should be 0.1uf not 0.01uf. so that might be worth a try I guess?
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RESET circuit tweaks
Re: RESET circuit tweaks
If it ain't broke, test it to Destruction.
Re: RESET circuit tweaks
I got it working. 
Have been testing using bench PSU at 5v. Cranked it up to 5.5v and the circuit is steady.
Have been testing using bench PSU at 5v. Cranked it up to 5.5v and the circuit is steady.
- Screen Shot 2018-11-10 at 20.46.50.png (22.01 KiB) Viewed 5352 times
Re: RESET circuit tweaks
well we got there in the end then Now you've fixed it I have to get distracted by X Factor...... *sigh*
If it ain't broke, test it to Destruction.
Re: RESET circuit tweaks
Yes - Thats the prototype board sorted. Now need to translate it to the reset board and STF as I think there are a few value changes to be done.Forgottenmyname wrote: Sat Nov 10, 2018 8:53 pm
Now you've fixed it I have to get distracted by X Factor...... *sigh*
Enjoy Xfactor
Re: RESET circuit tweaks
If it ain't broke, test it to Destruction.
Re: RESET circuit tweaks
Just catching up here... Doesn't seem right that it needs higher voltage to work.. Maybe some resistor is to high in value and its not charging the cap up ?
Re: RESET circuit tweaks
On the prototype board I am using 1K as per the Mega ST schematic as the pull up resistor connected to the reset switch. Apart from the pull-up on the ~Reset (Mega ST schematic and my test board) there are no other resistors.exxos wrote: Sat Nov 10, 2018 11:35 pm Just catching up here... Doesn't seem right that it needs higher voltage to work.. Maybe some resistor is to high in value and its not charging the cap up ?
Re: RESET circuit tweaks
What about 2 1k in series on the sense on pin 7 to bias it to 2.5v ?
Re: RESET circuit tweaks
Also pin 5 needs 10k pull up and pin 6 pull down according to the data sheet...
Re: RESET circuit tweaks
Gave that ago on 5V with no response. output just sat at 0Vexxos wrote: Sat Nov 10, 2018 11:59 pm What about 2 1k in series on the sense on pin 7 to bias it to 2.5v ?
Section 10 of the data sheet found by Forgottenmyname is interesting around having to terminate both outputs and also putting a resistor in series with the Charge Threshold capacitor http://www.ti.com/lit/ds/symlink/tl7705b.pdf