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TPS62140 low side FET failure

Wayne Chappell
Prodigy 30 points
Other Parts Discussed in Thread: TPS62140, TPS82130

Was this problem ever resolved.  

We have had a rash of similar issues where the Low Side FET fo the TPS62140 is shorted to ground after running for several hours.

We have built and tested about 200 devices, and after running for a few hours we've had about 10 or so failures in this way.  The rest of the design has been running for several years and we had just switched to the TPS62140 due another part obsolescence.

Any ideas of what might cause this failure mode?

  • 0
    TI__Guru**** 150900 points
    I split this post since it is about a different circuit. I don't believe there was any conclusion to the previous thread.

    There are lots of things that can break a power supply. Can you post your schematic, BOM, and layout?
  • 0 in reply to Chris Glaser
    Prodigy 30 points

     Here is the Schematic.   Pretty straight forward.


    BILL of Materials

    AML Part Num Assembly Assembly2 Value Reference Description Manufacturer Mfg Part Num PCB Footprint
    1430-0015 DNI DNI 10uF C29 Capacitor, Cer, 10uF, 25V,1206 TAIYO YUDEN TMK316BJ106KL-T CAP-1206
    1430-0069 22uF C30 Capacitor, 22uF,10V,20%,0805 TAIYO YUDEN LMK212BJ226MG-T CAP-0805
    1430-0069 DNI DNI 22uF C31 Capacitor, 22uF,10V,20%,0805 TAIYO YUDEN LMK212BJ226MG-T CAP-0805
    1430-0015 10uF C118 Capacitor, Cer, 10uF, 25V,1206 TAIYO YUDEN TMK316BJ106KL-T CAP-1206
    1430-0085 6800pF C163 CAP,6800pF,25V,0402,10%,X7R TAIYO YUDEN TMK105B7682KV-F CAP-0402
    1450-0052 2.2uH L2 Inductor, 2.2uH, 2.9A, SHLD, 4MM SMD BOURNS SRN4018-2R2M IND-2L-4X4-3P05
    1410-0162 1M R37 Resistor, 1M Ohm, ±1%, 0402 XICON 304-1.0M-RC RES-0402
    1410-0230 187K R38 Resistor, 187K Ohm, ±1%, 0402 YAGEO RC0402FR-07187KL RES-0402
    1410-0136 100K R217 Resistor, 100K, ±1%, 0402, 5/8W XICON 304-100K-RC RES-0402
    1410-0138 10K R255 Resistor, 10K Ohm, ±1%, 0402 YAGEO RC0402FR-0710KL RES-0402
    1200-0144 TPS62140 U5 IC REG BUCK ADJ 2A SYNC 16QFN TI TPS62140RGT QFN-17-3X3-P5-2P8

    LAYOUT

    After reviewing the layout I see a significant copper pour on the Switch node and for whatever reason C29 is not tied directly the PVIN pins.  Can that cause a device failure.

     

       

     

  • 0 in reply to Wayne Chappell
    TI__Guru**** 150900 points
    It's a little difficult to read the layout images (I can't see any vias for example) but it is clear that the input cap is not well placed/routed. Please see this app note for how to do a good PCB layout: www.ti.com/.../slyt614.pdf

    As well, you might look into using the TPS82130 module for an easier layout and overall simpler design.
  • 0 in reply to Chris Glaser
    Prodigy 30 points
    I did see that the input cap was not tied directly and have already talked to the design engineer about this layout.

    We had already started modifying boards yesterday by manually placing 220nF || 220nF (used 2 caps to reduce parasitic inductance) directly to the input pin on 18 devices that had previously failed, a couple had failed twice even. 12 hours burn-in so far and no failures.

    I think the poor input cap placement is our issue. Great app note by the way, I've passed in on.