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Original question:

DCR021205

DCR021205: DCR021205P-U

Robert Pearcey
Prodigy 40 points
Part Number: DCR021205

Can you provide some info on TI PN DCR021205P-U, which is a 2W, 12V to 5V converter.

 

Occasionally, we get some parts that initially test ok with 5V output but when integrated in the next level assembly, the 5V fails, no output.  It would appear as a loading issue but only the DC/DC part is changed and then the system function is established.  It may be a transient load that pulls it down but it stays down.  The PCB was tested in 3 assemblies prior to being replaced, all with the same results, so it's not likely a problem with the next level assembly.  We do have a fair amount of capacitive load, 75uf on board.

 

Visual inspection of the device & connections looks good.  The part is marked with Burr-Brown name and all recent failures have a date code of 88ZE09H.  We’ve had about 5 recurrences recently so wondering if anything has changed or maybe these are old parts being used.

 

  • 0
    TI__Mastermind 25590 points

    Robert,

    Can you please probe each pin and let us know the voltage you find. Please also share the layout if possible.

    Thanks,

    -Sam

  • 0
    TI__Guru 50120 points

    Hi Robert,

    In addition to Sam's question of the voltage measurements on each pin, can you answer the following?

    1. Can you do a continuity check between Pin 8 (output ground) and Pin 9 (voltage output) to make sure there is no internal short?
    2. When the device is integrated in the next level assembly, are you pulling the same amount of current (400mA)? These isolated DC/DC converters need some amount of preload current to regulate properly. 
    3. What is the process when you generate the device and what is reflow profile between initial test and "next level assembly"? 

    Regards,

    Jimmy 

  • 0 in reply to Jimmy Hua
    Prodigy 40 points

    1. No shorts found

    2. Yes, next level assembly connects a small PCB with 1 integrator IC and a photo diode.  Little capacitance added.  PCBs are connected by a cable but cables and board show no shorts.

    3. Need to contact our CM for reflow profile but we use a high volume of boards.  What's the concern, the peak temp & duration??

  • 0 in reply to Samuel Jaffe
    Prodigy 40 points

    It's a double sided PCB with output caps and input cap & inductor directly below the DC/DC part.  Parts are separated by the length of the converter.

    Will work on taking measurements.

  • 0 in reply to Robert Pearcey
    TI__Guru 50120 points

    Hi Robert,

    The datasheet has a specification on the absolute maximum reflow solder temperature of 260C. I want to make sure that during the reflow process these parts aren't somehow damaged because of peak temperature above abs max. 

    The schematic that you've provided looks similar to the typical schematic detailed in Figure 6. 

    When you get more information on the voltage measurements that Sam suggested, please let me know.

    Regards,

    Jimmy 

  • 0 in reply to Jimmy Hua
    TI__Guru 50120 points

    Hi Robert,

    Were you able to get any more voltage measurements from each pin and the peak voltage/ reflow profile of the assembly?

    I have not heard back from you for some time and would like to get an update.

    Regards,

    Jimmy 

  • 0 in reply to Jimmy Hua
    Prodigy 40 points

    Hi Jimmy,

    Thanks for checking back.  Looking like it may be an assembly issue.

    When I studied the assembly, I found small burn marks on the tantalum bulk cap & an associated burn mark on the adjacent housing.

    Appears the PCB can move more than expected.  Initial fix was mylar tape on the housing and/or PCB edge.  With that, no manufacturing problems were reported last week.

    I need to get confirmation this solved the problem but it looks like that was the problem.

    Thanks for your help.

    Bob Pearcey

  • 0 in reply to Robert Pearcey
    TI__Guru 50120 points

    Hi Robert,

    Thank you for the update. 

    If you have any remaining questions about the power module, please feel free to reply to this message and the thread will reopen for further support.

    I will be closing this thread.

    Regards,

    Jimmy