Reliability of TI/BB DCP02 DC-DC converters

S

Spehro Pefhany

Guest
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 150°C 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"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
On Tue, 06 Apr 2004 15:37:27 GMT, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> 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 150°C 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
Click to expand...
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.
greg@guesswhichwordgoeshere.com
 
On Tue, 06 Apr 2004 12:50:50 -0400, the renowned Greg Neff
<greg@microsym.com> wrote:

On Tue, 06 Apr 2004 15:37:27 GMT, Spehro Pefhany
speffSNIP@interlogDOTyou.knowwhat> 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 150°C 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.
Click to expand...
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 85°C.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
Spehro Pefhany wrote:
On Tue, 06 Apr 2004 12:50:50 -0400, the renowned Greg Neff
greg@microsym.com> wrote:


On Tue, 06 Apr 2004 15:37:27 GMT, Spehro Pefhany
speffSNIP@interlogDOTyou.knowwhat> 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 150°C 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 85°C.
Click to expand...
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.
 
On Tue, 06 Apr 2004 10:40:11 -0700, Jim Stewart <jstewart@jkmicro.com>
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.
Click to expand...
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/folders/print/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.
greg@guesswhichwordgoeshere.com
 
On Tue, 06 Apr 2004 10:40:11 -0700, the renowned Jim Stewart
<jstewart@jkmicro.com> 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.
Click to expand...
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"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
Greg Neff <greg@microsym.com> wrote in message news:<n3r5705k1k0i4kr05ptca0o79lfg5mt0b1@4ax.com>...
On Tue, 06 Apr 2004 10:40:11 -0700, Jim Stewart <jstewart@jkmicro.com
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/folders/print/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.
greg@guesswhichwordgoeshere.com
Click to expand...
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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