Quantcast

Tobi schematic error

classic Classic list List threaded Threaded
3 messages Options
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Tobi schematic error

the suicidal eggroll
I've just finished prototyping a custom Overo expansion board based on the Tobi, and in the process discovered a problem with the published schematic for the Tobi dating back many revisions (not sure how far back it's a problem, but it's far).

The 3.3v regulator used on the Tobi is the TPS62111, a fixed 3.3v output DC/DC regulator.  According to the data sheet:
http://www.ti.com/lit/ds/slvs585c/slvs585c.pdf

FB is the feedback pin that controls the output voltage.  On the adjustable versions of the regulator (TPS62110, TPS62113) this should be connected to a voltage divider to set the output voltage, but on the fixed output versions of the regulator (TPS62111 and TPS62112) it should be connected directly to Vout.

The physical Tobi board is constructed correctly, C12 and R34 are not populated and R33 is a 0 ohm jumper to short FB to Vout.  However, the Tobi schematic does not reflect this.  The schematic shows a voltage divider between R33 and R34 which should not be there.

When the circuit shown in the schematic is implemented, the voltage divider causes the TPS62111 to ramp up Vout since FB is so low.  My 3.3v rail was hovering around 4.9v until I discovered this problem.  When I removed R34 and C12 and replaced R33 with a jumper, the 3.3v rail dropped down to normal.

Like I said above, the Tobi board itself is fine, but the schematic posted on pubs.gumstix.com does not match what's actually being built and sold.
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: Tobi schematic error

Neil MacMunn
Hello,

Thanks for bringing this to our attention. There is a note in the Tobi readme about possible BOM substitutions but it appears the schematic shows an invalid configuration. I will change this to reflect our most common setup (TPS62111).


Sorry for the confusion,

-
Neil


On Fri, Aug 30, 2013 at 2:42 PM, the suicidal eggroll <[hidden email]> wrote:
I've just finished prototyping a custom Overo expansion board based on the
Tobi, and in the process discovered a problem with the published schematic
for the Tobi dating back many revisions (not sure how far back it's a
problem, but it's far).

The 3.3v regulator used on the Tobi is the TPS62111, a fixed 3.3v output
DC/DC regulator.  According to the data sheet:
http://www.ti.com/lit/ds/slvs585c/slvs585c.pdf

FB is the feedback pin that controls the output voltage.  On the adjustable
versions of the regulator (TPS62110, TPS62113) this should be connected to a
voltage divider to set the output voltage, but on the fixed output versions
of the regulator (TPS62111 and TPS62112) it should be connected directly to
Vout.

The physical Tobi board is constructed correctly, C12 and R34 are not
populated and R33 is a 0 ohm jumper to short FB to Vout.  However, the Tobi
schematic does not reflect this.  The schematic shows a voltage divider
between R33 and R34 which should not be there.

When the circuit shown in the schematic is implemented, the voltage divider
causes the TPS62111 to ramp up Vout since FB is so low.  My 3.3v rail was
hovering around 4.9v until I discovered this problem.  When I removed R34
and C12 and replaced R33 with a jumper, the 3.3v rail dropped down to
normal.

Like I said above, the Tobi board itself is fine, but the schematic posted
on pubs.gumstix.com does not match what's actually being built and sold.



--
View this message in context: http://gumstix.8.x6.nabble.com/Tobi-schematic-error-tp4967841.html
Sent from the Gumstix mailing list archive at Nabble.com.

------------------------------------------------------------------------------
Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more!
Discover the easy way to master current and previous Microsoft technologies
and advance your career. Get an incredible 1,500+ hours of step-by-step
tutorial videos with LearnDevNow. Subscribe today and save!
http://pubads.g.doubleclick.net/gampad/clk?id=58040911&iu=/4140/ostg.clktrk
_______________________________________________
gumstix-users mailing list
[hidden email]
https://lists.sourceforge.net/lists/listinfo/gumstix-users


------------------------------------------------------------------------------
Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more!
Discover the easy way to master current and previous Microsoft technologies
and advance your career. Get an incredible 1,500+ hours of step-by-step
tutorial videos with LearnDevNow. Subscribe today and save!
http://pubads.g.doubleclick.net/gampad/clk?id=58040911&iu=/4140/ostg.clktrk
_______________________________________________
gumstix-users mailing list
[hidden email]
https://lists.sourceforge.net/lists/listinfo/gumstix-users
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: Tobi schematic error

the suicidal eggroll
I didn't notice note #2 when I was looking through that readme during the design phase, odd.  I'm glad that there was a note about it though.

No worries, no damage was caused by the temporarily high 3.3v rail on my setup.  I was testing the voltages on the board before the Gumstix had been inserted, and there were only 5 prototype boards that needed fixing once the problem was identified, which just took a few minutes.

On 08/30/2013 04:03 PM, Neil MacMunn wrote:
Hello,

Thanks for bringing this to our attention. There is a note in the Tobi readme about possible BOM substitutions but it appears the schematic shows an invalid configuration. I will change this to reflect our most common setup (TPS62111).


Sorry for the confusion,

-
Neil


On Fri, Aug 30, 2013 at 2:42 PM, the suicidal eggroll <[hidden email]> wrote:
I've just finished prototyping a custom Overo expansion board based on the
Tobi, and in the process discovered a problem with the published schematic
for the Tobi dating back many revisions (not sure how far back it's a
problem, but it's far).

The 3.3v regulator used on the Tobi is the TPS62111, a fixed 3.3v output
DC/DC regulator.  According to the data sheet:
http://www.ti.com/lit/ds/slvs585c/slvs585c.pdf

FB is the feedback pin that controls the output voltage.  On the adjustable
versions of the regulator (TPS62110, TPS62113) this should be connected to a
voltage divider to set the output voltage, but on the fixed output versions
of the regulator (TPS62111 and TPS62112) it should be connected directly to
Vout.

The physical Tobi board is constructed correctly, C12 and R34 are not
populated and R33 is a 0 ohm jumper to short FB to Vout.  However, the Tobi
schematic does not reflect this.  The schematic shows a voltage divider
between R33 and R34 which should not be there.

When the circuit shown in the schematic is implemented, the voltage divider
causes the TPS62111 to ramp up Vout since FB is so low.  My 3.3v rail was
hovering around 4.9v until I discovered this problem.  When I removed R34
and C12 and replaced R33 with a jumper, the 3.3v rail dropped down to
normal.

Like I said above, the Tobi board itself is fine, but the schematic posted
on pubs.gumstix.com does not match what's actually being built and sold.



--
View this message in context: http://gumstix.8.x6.nabble.com/Tobi-schematic-error-tp4967841.html
Sent from the Gumstix mailing list archive at Nabble.com.

------------------------------------------------------------------------------
Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more!
Discover the easy way to master current and previous Microsoft technologies
and advance your career. Get an incredible 1,500+ hours of step-by-step
tutorial videos with LearnDevNow. Subscribe today and save!
http://pubads.g.doubleclick.net/gampad/clk?id=58040911&iu=/4140/ostg.clktrk
_______________________________________________
gumstix-users mailing list
[hidden email]
https://lists.sourceforge.net/lists/listinfo/gumstix-users



------------------------------------------------------------------------------
Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more!
Discover the easy way to master current and previous Microsoft technologies
and advance your career. Get an incredible 1,500+ hours of step-by-step
tutorial videos with LearnDevNow. Subscribe today and save!
http://pubads.g.doubleclick.net/gampad/clk?id=58040911&iu=/4140/ostg.clktrk


_______________________________________________
gumstix-users mailing list
[hidden email]
https://lists.sourceforge.net/lists/listinfo/gumstix-users


------------------------------------------------------------------------------
Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more!
Discover the easy way to master current and previous Microsoft technologies
and advance your career. Get an incredible 1,500+ hours of step-by-step
tutorial videos with LearnDevNow. Subscribe today and save!
http://pubads.g.doubleclick.net/gampad/clk?id=58040911&iu=/4140/ostg.clktrk
_______________________________________________
gumstix-users mailing list
[hidden email]
https://lists.sourceforge.net/lists/listinfo/gumstix-users
Loading...