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Reliability of TI/BB DCP02 DC-DC converters

 
 
Spehro Pefhany
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      04-06-2004, 03:37 PM

Hello:-

I'm just wrapping up a design that includes a DCP-02 12V:5V isolated
unregulated 600kHz DC-DC converter. Everything seems straightforward,
the unit is supposed to include thermal shutdown at 150C chip
temperature which should typically protect the converter if the output
is inadvertently overloaded. This project will see wide Ta range.

However, I've just run across a tray of bad DCP-02 units of unknown
origin- containing about 50 duff units, and also I recently came
across a hobbyist who had problems with his dying recently. This can
be explained away by assuming that those people were not obeying the
rather strict abs. max. input voltage rating (15V for the 12V units,
for example), but I'd sure like to know any info to the contrary.

Thanks!

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
(E-Mail Removed) Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
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Greg Neff
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      04-06-2004, 04:50 PM
On Tue, 06 Apr 2004 15:37:27 GMT, Spehro Pefhany
<(E-Mail Removed)> wrote:

>
>Hello:-
>
>I'm just wrapping up a design that includes a DCP-02 12V:5V isolated
>unregulated 600kHz DC-DC converter. Everything seems straightforward,
>the unit is supposed to include thermal shutdown at 150C chip
>temperature which should typically protect the converter if the output
>is inadvertently overloaded. This project will see wide Ta range.
>
>However, I've just run across a tray of bad DCP-02 units of unknown
>origin- containing about 50 duff units, and also I recently came
>across a hobbyist who had problems with his dying recently. This can
>be explained away by assuming that those people were not obeying the
>rather strict abs. max. input voltage rating (15V for the 12V units,
>for example), but I'd sure like to know any info to the contrary.
>
>Thanks!
>
>Best regards,
>Spehro Pefhany


We don't use the specific DCP021205 that you are asking about, but we
have used a few thousand DCP02 converters (different voltages) over
the past few years. These are used in rail car applications, with
ambient temperatures in the enclosure getting close to +85C. We are
required to not exceed 50% of the load rating on any power supply or
DC-DC converter, so we don't push them as hard as many people would.
That having been said, we have been very happy with their reliability.
As far as I know, we have not had any fail yet in the field, and I
haven't heard about any fallout in production test and burn in.




================================

Greg Neff
VP Engineering
*Microsym* Computers Inc.
(E-Mail Removed)
 
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Spehro Pefhany
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Posts: n/a
 
      04-06-2004, 05:36 PM
On Tue, 06 Apr 2004 12:50:50 -0400, the renowned Greg Neff
<(E-Mail Removed)> wrote:

>On Tue, 06 Apr 2004 15:37:27 GMT, Spehro Pefhany
><(E-Mail Removed)> wrote:
>
>>
>>Hello:-
>>
>>I'm just wrapping up a design that includes a DCP-02 12V:5V isolated
>>unregulated 600kHz DC-DC converter. Everything seems straightforward,
>>the unit is supposed to include thermal shutdown at 150C chip
>>temperature which should typically protect the converter if the output
>>is inadvertently overloaded. This project will see wide Ta range.
>>
>>However, I've just run across a tray of bad DCP-02 units of unknown
>>origin- containing about 50 duff units, and also I recently came
>>across a hobbyist who had problems with his dying recently. This can
>>be explained away by assuming that those people were not obeying the
>>rather strict abs. max. input voltage rating (15V for the 12V units,
>>for example), but I'd sure like to know any info to the contrary.
>>
>>Thanks!
>>
>>Best regards,
>>Spehro Pefhany

>
>We don't use the specific DCP021205 that you are asking about, but we
>have used a few thousand DCP02 converters (different voltages) over
>the past few years. These are used in rail car applications, with
>ambient temperatures in the enclosure getting close to +85C. We are
>required to not exceed 50% of the load rating on any power supply or
>DC-DC converter, so we don't push them as hard as many people would.
>That having been said, we have been very happy with their reliability.
>As far as I know, we have not had any fail yet in the field, and I
>haven't heard about any fallout in production test and burn in.


Thanks a lot, Greg, that's what I needed to hear- from the right kind
of source. We won't be pushing them either, power-wise, but the Ta may
approach 85C.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
(E-Mail Removed) Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
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Jim Stewart
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Posts: n/a
 
      04-06-2004, 05:40 PM
Spehro Pefhany wrote:
> On Tue, 06 Apr 2004 12:50:50 -0400, the renowned Greg Neff
> <(E-Mail Removed)> wrote:
>
>
>>On Tue, 06 Apr 2004 15:37:27 GMT, Spehro Pefhany
>><(E-Mail Removed)> wrote:
>>
>>
>>>
>>>Hello:-
>>>
>>>I'm just wrapping up a design that includes a DCP-02 12V:5V isolated
>>>unregulated 600kHz DC-DC converter. Everything seems straightforward,
>>>the unit is supposed to include thermal shutdown at 150C chip
>>>temperature which should typically protect the converter if the output
>>>is inadvertently overloaded. This project will see wide Ta range.
>>>
>>>However, I've just run across a tray of bad DCP-02 units of unknown
>>>origin- containing about 50 duff units, and also I recently came
>>>across a hobbyist who had problems with his dying recently. This can
>>>be explained away by assuming that those people were not obeying the
>>>rather strict abs. max. input voltage rating (15V for the 12V units,
>>>for example), but I'd sure like to know any info to the contrary.
>>>
>>>Thanks!
>>>
>>>Best regards,
>>>Spehro Pefhany

>>
>>We don't use the specific DCP021205 that you are asking about, but we
>>have used a few thousand DCP02 converters (different voltages) over
>>the past few years. These are used in rail car applications, with
>>ambient temperatures in the enclosure getting close to +85C. We are
>>required to not exceed 50% of the load rating on any power supply or
>>DC-DC converter, so we don't push them as hard as many people would.
>>That having been said, we have been very happy with their reliability.
>>As far as I know, we have not had any fail yet in the field, and I
>>haven't heard about any fallout in production test and burn in.

>
>
> Thanks a lot, Greg, that's what I needed to hear- from the right kind
> of source. We won't be pushing them either, power-wise, but the Ta may
> approach 85C.


Another issue you may want to look at is the size
of any output capacitor that you put on the unit.
I know that I didn't read the data sheet carefully
with some Power Conversions units and burned up a
couple samples before I caught the problem. Too
large of an output capacitor will lunch the driver
transistors on startup. This might have happened
to your tray of parts.





 
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Greg Neff
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Posts: n/a
 
      04-06-2004, 06:13 PM
On Tue, 06 Apr 2004 10:40:11 -0700, Jim Stewart <(E-Mail Removed)>
wrote:

(snip)
>
>Another issue you may want to look at is the size
>of any output capacitor that you put on the unit.
>I know that I didn't read the data sheet carefully
>with some Power Conversions units and burned up a
>couple samples before I caught the problem. Too
>large of an output capacitor will lunch the driver
>transistors on startup. This might have happened
>to your tray of parts.
>
>
>
>


We have been using ceramic capacitors (a few uF) on the output.

I would also recommend reading the application notes listed on the
DCP02 product page:

http://focus.ti.com/docs/prod/folder...dcp021205.html

These things can generate a lot of RFI, so you have to watch this. The
transformer has some healthy ringing at around 55MHz. Using ferrite
bead and ceramic cap filters on the outputs is strongly recommended.
If you have more than one DCP02 in a box then make sure that they are
synchronized (best to use polyphase) to avoid beat frequencies, and to
avoid simultaneous current peaks on the input supply.


================================

Greg Neff
VP Engineering
*Microsym* Computers Inc.
(E-Mail Removed)
 
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Spehro Pefhany
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Posts: n/a
 
      04-06-2004, 06:16 PM
On Tue, 06 Apr 2004 10:40:11 -0700, the renowned Jim Stewart
<(E-Mail Removed)> wrote:

>Another issue you may want to look at is the size
>of any output capacitor that you put on the unit.
>I know that I didn't read the data sheet carefully
>with some Power Conversions units and burned up a
>couple samples before I caught the problem. Too
>large of an output capacitor will lunch the driver
>transistors on startup. This might have happened
>to your tray of parts.


Thanks. I'm actually under the recommended value for this. That
doesn't sound like a very good design that would die from too much
capacitance on the output. I'd expect them to be able to take a dead
short without dying, let alone just charging up a cap. 8-(

The tray of parts came from another company (now defunct) so I'll
probably never know what they were up to. Date codes are all 1999.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
(E-Mail Removed) Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
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Paul Mathews
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Posts: n/a
 
      04-08-2004, 03:15 PM
Greg Neff <(E-Mail Removed)> wrote in message news:<(E-Mail Removed)>. ..
> On Tue, 06 Apr 2004 10:40:11 -0700, Jim Stewart <(E-Mail Removed)>
> wrote:
>
> (snip)
> >
> >Another issue you may want to look at is the size
> >of any output capacitor that you put on the unit.
> >I know that I didn't read the data sheet carefully
> >with some Power Conversions units and burned up a
> >couple samples before I caught the problem. Too
> >large of an output capacitor will lunch the driver
> >transistors on startup. This might have happened
> >to your tray of parts.
> >
> >
> >
> >

>
> We have been using ceramic capacitors (a few uF) on the output.
>
> I would also recommend reading the application notes listed on the
> DCP02 product page:
>
> http://focus.ti.com/docs/prod/folder...dcp021205.html
>
> These things can generate a lot of RFI, so you have to watch this. The
> transformer has some healthy ringing at around 55MHz. Using ferrite
> bead and ceramic cap filters on the outputs is strongly recommended.
> If you have more than one DCP02 in a box then make sure that they are
> synchronized (best to use polyphase) to avoid beat frequencies, and to
> avoid simultaneous current peaks on the input supply.
>
>
> ================================
>
> Greg Neff
> VP Engineering
> *Microsym* Computers Inc.
> (E-Mail Removed)


Had very similar experience with EMI and these parts. During startup,
current spikes reach 2.5A, regardless of output loading (or the lack
thereof). If your power supply comes up slowly, the converters will
produce these spikes for the duration. Very high fields are found
near the center of the modules, and parasitic capacitance from input
to output is something like 30pF, IIRC. So, there's a need to bypass
the common mode current. For us, the most effective approach was to
put a patch of copper immediately underneath the module, unconnected
to any pins. This provides a return path for the CM currents without
injecting any into either ground plane. We also ended up using a high
capacitance MLCC (10uF Y5V) to bypass the primary side. Lytics and Ta
caps had too much ESR.
Paul Mathews
 
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Joerg
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      04-12-2004, 06:45 PM
Spehro, I believe the DCP02 only has a thermal shutdown which may not be fast
enough to protect the converter against a short. But the sync pin allows to stop
the oscillator so I guess it could be tied into the usual current sense scheme
if you have to protect against overload.

Personally I am not a fan of such integrated DC-DC solutions, and not just
because they are usually $5 and up per device. But at least these things can be
synchronized.

Regards, Joerg.

 
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