The TL7702A appears to have a threshold of 2.53V & is designed to operate in systems down to 3.5V - according to the datasheet. But you are having problems with a 1.2V supply. Doesn't quite add up without additional supplies and presumably interconnections. I still think it's likely to be a risetime issue on the 1.2V supply. If it works OK with a manual reset, what time delay have you for the power-on reset - have you tried making it longer so that things are a bit more stable before the reset releases? RP On 25 June 2014 20:38, Jahn wrote: > Thank you for the replies > > @Richard > > By "on the edge" I meant that is the reset or brownout protection > > level set very close to the operating voltage. If so then minor dips > > in the supply could cause a reset. A probe on the reset line should > > tell you what is happening here and you've probably already done that. > > The board uses TL7702A SUPPLY-VOLTAGE SUPERVISOR. > I used that TL7702A to reset CPU ( non RESET pin of > TL7702A goes to CPU) > but do not know how to check if there is any brownout protection > level set very close to the operating voltage. > Can you please let me know how to check that? > > > > > @Colin > >Is it worth checking that the uP HALT line isn't activated and that the > >crystal actually attempts to oscillate? > Do you mean RESET pin of CPU > > Thank you for help > > > > > > > > > > On 24 June 2014 21:53, Jahn wrote: > > > > > Thank you all for the replies > > > > > > > Does the CPU start, if you reset it while keeping the power on? If > > > > so, most likely the problem is slow rise time. > > > I tried to reset CPU several times, but still does not start.But > > > when I use the correct power supply, it starts when resetting. > > > > > > > Could be some sort of inrush current effect. Also, if there is a > > > > secondary power supply downstream, it may require the input to > > > > have a fast risetime. > > > Yes, there are more powers but I reset CPU while keeping power on, > > > so the risetime should be OK. > > > > > > >Especially if power supply sequencing is important. > > > Not sure if the sequencing is important or not, but when I reset > > > CPU(keeping power on and using the working voltage supply), it > > > started. So, I do not think, in my case, the sequence is important. > > > > > > > Check that your crystal is operating OK. > > > Do you mean the crystal of the mainboard? There is NO crystal that > > > uses the Asynchronous Step-Down Regulator > > > > > > >Dust/dirt providing a > > > > leakage path & preventing correct startup? > > > I hotair reflowed the power supply part already > > > > > > > Another thing to check > > > > would be the reset/brownout arrangements - could be on the edge? > > > Can you explain a little more? > > > Thanks > > > > > > > > > > Do you have any other idea? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I have a Linux embeded board that uses > > > > > FP6116 Asynchronous Step-Down Regulator > > > > > a datasheet is here > > > > > http://www.micro-bridge.com/data/Feeling-tech/FP6116.pdf > > > > > > > > > > In this design , that Asynchronous Step-Down Regulator should > > > > > supply 1,2V for CPU on this board. It worked for some time but > > > > > now it stopped. So, I measured voltage and that Asynchronous > > > > > Step-Down Regulator still supply 1.2V, yet CPU does not start. > > > > > But when I use a different source of 1.2V, the CPU starts. So, I > > > > > am rather confused. I can measure the same voltages, and more or > > > > > less the same spikes( using oscilloscope), yet different > > > > > results. > > > > > > > > > > Can anyone suggest any solution to that problem? > > > > > Thanks > > > > > -- > > > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > > > > View/change your membership options at > > > > > http://mailman.mit.edu/mailman/listinfo/piclist > > > > > > > > -- > > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > > > View/change your membership options at > > > > http://mailman.mit.edu/mailman/listinfo/piclist > > > > > > > > > -- > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > > View/change your membership options at > > > http://mailman.mit.edu/mailman/listinfo/piclist > > > > > -- > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .