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UC3909 Schematic Review

Pradhan Rivankar
Expert 1080 points

Hello All

 

Can somebody get the attached schematic based on the UC3909 reveiwed.

Need the urgent support so that I can move further with my design.

Thanking in advance and awaiting for the valuable inputs.

Thanks and regards

revised battery charger UC3909.pdf
  • 0
    Expert 1080 points

    Hi All again

     

    There is a layout on the second page. Please review that also.

     

    Thanks and regards

     

    Pradhan

  • 0 in reply to Pradhan Rivankar
    TI__Guru**** 150950 points

    It looks like this design was based on this app note's circuit: http://focus.ti.com/lit/an/slua098/slua098.pdf

    However, there are some differences and major mistakes.  The drain and source of Q2 are backwards.  Also, Q1 is the same part number as Q2.  This is a major mistake as these transistors serve very different purposes.  As explained in the app note, Q2 is a small signal transistor used for inversion.  Q1 is the power transistor that will pass the switching current and dissipate lots of power.  If they picked the same part for each of these (in a SOT-23 package), then they need to contact a design services group to do their design for them.

  • 0 in reply to Chris Glaser
    TI__Genius 12961 points

    Thanks Chris!

    (Pradhan is our Distributor FAE and is out of town so I am following up for this - so that the customer gets a timely response.)

    On the layout of the circuit, I see a lot of long paths and loops. Component placement and Routing needs to be improved.

    Can you please share your comments on the layout also. I could not find any details about that in the app note.

    Thanks & Regards,

    Sanjay Pithadia

  • 0 in reply to Sanjay Pithadia
    TI__Guru**** 150950 points

    Yes, I agree that their layout is poor.  D2 and L1 are far away from Q1 and are connected with narrow and long traces.

    Sanjay, you are more than qualified to evaluate their layout and schematics.  This is simply a controller driving a buck power stage.  So, layout techniques for buck power stages and for sensitive analog signals can be applied.  I would prefer that you evaluate their design first and talk with the customer about it.

    But from what I have seen, they do not understand the basics of power electronics.  Because of this, I recommend they contact the design services group that can do this design for them.