Forums

Olimex USB JTAG device kills laptop motherboard ?

Started by armdeveloper September 17, 2007
I'm using an LPC 2138 to drive some high powered MOSFETs, sinking up to
20 amps.

I'm using an Olimex USB JTAG device for programming and debugging.

Everything works fine with the debugger and such. Only thing is that
the motherboard went out on my laptop about a couple months ago and now
the video driver just failed.

Is this a co-incidence or is there a way the debugger could damage the
laptop ?

Thanks

An Engineer's Guide to the LPC2100 Series

There's nothing at fault with the JTAG device.

But if you're debugging a circuit, then you are in electrical contact with
that circuit (unless _you_ have made provision for opto-isolation
or equivalent).

If your circuit has nasty voltages and/or currents, and they get into
your PC, who knows what will go bang.

It would not be difficult to arrange opto-isolation for JTAG. But I do
not know of any interfaces that provide it as standard.

Sorry if that's not the answer you wanted.
- Danish
--- In l..., armdeveloper wrote:
>
> I'm using an LPC 2138 to drive some high powered MOSFETs, sinking up to
> 20 amps.
>
> I'm using an Olimex USB JTAG device for programming and debugging.
>
> Everything works fine with the debugger and such. Only thing is that
> the motherboard went out on my laptop about a couple months ago and now
> the video driver just failed.
>
> Is this a co-incidence or is there a way the debugger could damage the
> laptop ?
>
> Thanks
>
On Mon, 2007-09-17 at 19:43 +0000, Danish Ali wrote:
> There's nothing at fault with the JTAG device.
>
> But if you're debugging a circuit, then you are in electrical contact
> with
> that circuit (unless _you_ have made provision for opto-isolation
> or equivalent).
>
> If your circuit has nasty voltages and/or currents, and they get into
> your PC, who knows what will go bang.
>
> It would not be difficult to arrange opto-isolation for JTAG. But I do
> not know of any interfaces that provide it as standard.
>
> Sorry if that's not the answer you wanted.

What if one connected the JTAG device to a hub instead of to the laptop
directly.

Has anyone seen an opto isolated USB device ? I need 3 of them, one for
the JTAG, one for the USB serial port link and one for the USB port on
the device.

Hmmm....
--- In l..., armdeveloper wrote:
>
> I'm using an LPC 2138 to drive some high powered MOSFETs, sinking up to
> 20 amps.

20 amps. Right. Optos required.

> I'm using an Olimex USB JTAG device for programming and debugging.
>
> Everything works fine with the debugger and such. Only thing is that
> the motherboard went out on my laptop about a couple months ago and now
> the video driver just failed.
>
> Is this a co-incidence or is there a way the debugger could damage the
> laptop ?
>

Turn on 20 amps and anything might happen, (especially if turned on
quickly - spikes and EMP everywhere). Try very hard to make sure that
there is no continuous link of copper/silicon joining your laptop to
any side of the MOSFET/load.

What kind of load is on the MOSFET supply, and how fast do you turn it on?

Rgds,
Martin
At 01:13 PM 9/17/2007 -0600, armdeveloper wrote:
>I'm using an LPC 2138 to drive some high powered MOSFETs, sinking up to
>20 amps.

That's likely the issue. You may produce a significant voltage spike on
turn off, depending on how good your suppression is. Unsuppressed with a
1uS turn off and 10nH of inductance gives a voltage spike of gives only
0.2V spike but if you are driving a motor your inductance will be a lot
higher at that low a current mH wouldn't be surprising, all of a sudden the
voltage spike is 1000's of volts and usually some gives before it gets that
high. Suppression is a good thing :)
>I'm using an Olimex USB JTAG device for programming and debugging.
I have used real ICE's at higher currents but always with trepidation, one
wrong move and so-long $10,000 worth of ICE. What I usually try to do in
these cases is use ICE sparingly for simple startup and mode switch
problems. It's really not a good idea to single step through switching
code when that can result in an excess of current anyway (flames from power
board == bad). The rest is (mostly) easily dealt with over an (isolated)
serial port and with a little thought. The serial download abilities of
these chips complements that nicely. Don't let JTAG handicap your use of
your brain.

Robert

Another sign of the end of civilization, our technical magazines are
getting chatty
From an EETimes product descriptions 2006/08/09
".... systems that can sample gobs of inputs simultaneously"
Now just what is the technical definition for gobs again?
http://www.aeolusdevelopment.com/
maybe using a powered USB hub would help isolate

----- Original Message -----
From: Danish Ali
Date: Monday, September 17, 2007 12:48 pm
Subject: [lpc2000] Re: Olimex USB JTAG device kills laptop motherboard ?
To: l...

> There's nothing at fault with the JTAG device.
>
> But if you're debugging a circuit, then you are in electrical
> contact with
> that circuit (unless _you_ have made provision for opto-isolation
> or equivalent).
>
> If your circuit has nasty voltages and/or currents, and they get into
> your PC, who knows what will go bang.
>
> It would not be difficult to arrange opto-isolation for JTAG. But I do
> not know of any interfaces that provide it as standard.
>
> Sorry if that's not the answer you wanted.
> - Danish
> --- In l..., armdeveloper wrote:
> >
> > I'm using an LPC 2138 to drive some high powered MOSFETs, sinking
> up to
> > 20 amps.
> >
> > I'm using an Olimex USB JTAG device for programming and
> debugging.
> >
> > Everything works fine with the debugger and such. Only thing is
> that> the motherboard went out on my laptop about a couple months
> ago and now
> > the video driver just failed.
> >
> > Is this a co-incidence or is there a way the debugger could
> damage the
> > laptop ?
> >
> > Thanks
>
--- In l..., stevech@... wrote:
> maybe using a powered USB hub would help isolate

Why should a hub isolate something? May be you make a sacrify instead
of the motherboard. But only may be! You can't be sure.
There are so many ways to peek failiures backwards. The only thing
that will help is to isolate the JTAG with optocouplers or similar
isolating devices (icouplers & more)

Martin