[SI-LIST] Re: Reset problem with power supply
- From: olaney@xxxxxxxx
- To: for_si2003@xxxxxxxxx
- Date: Fri, 5 Dec 2008 12:57:13 -0800
Cable inductance absolutely should not be an issue. If it actually is,
be grateful that you found a design flaw before you reached production!
This might be related to the power risetime. Your POR circuit needs to
operate properly even if you slowly bring the voltage up manually. Some
circuits depend on fast power risetime to operate properly, and work
OK... most of the time. The worst ones capacitor couple the voltage bus
into a transistor. Not only do these fail to reset on a slow rise, if an
aluminum electrolytic cap is used, the value will drop with age as it
dries out and eventually the circuit won't work even for normal supply
risetime. A Schmitt trigger is a good basis for a bullet-proof approach,
as are any number of supervisor ICs that also check for overvoltage,
brown-out, and the like.
In any instance, if you can section the power distribution, start by
running everything off the bench supply, then one by one move each
section to power through the cable. When the problem reappears you have
found where to dig deeper. Power up and down between each change, rather
than doing this with a live circuit.
Orin Laney
On Fri, 5 Dec 2008 12:39:22 -0800 (PST) V S <for_si2003@xxxxxxxxx>
writes:
> When I power my board using a bench power supply it boots. When I try
> to plug in the cable, with the one end of the cable hooked to the
> same power supply in power on position it does not. My question is
> what difference cable inductance makes ? The failure looks like
> between processor and Flash core, as, the processor is always alive.
>
> The processor is freescale MX27. I am using national Semi LM2717-ADJ
> IC to generate 1.8V for memory IO, 1.5V for core and PLL, 2.775V for
> processor IO and 3.15 for other IO. A POR is generated using Schimtt
> Trigger. The HRESET is generated using the same schmitt Trigger
> 74LCX07MX.
>
> Any one faced similar situation ?
>
>
>
>
>
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