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TPS62143 drawing too much current, getting hot, but still working!

Jon Watkins
Prodigy 120 points
Other Parts Discussed in Thread: TPS62143, TPS62130, TPS62140

I'm working on a new design and am trialling a TPS62143. I'm just testing a couple of prototype boards and have come across an unusual problem which is knocking my confidence on this part.

I built up 2 boards and both worked fine. However I was probing around on one with a multimeter and when I finished I noticed the circuit drawing far more current - for about a 6V input it was drawing a current around 200mA for a circuit that only consumes about 5mA (there is another circuit that is plugged in that takes upwards of 1A hance the high current requirement). My first thought was I must have shorted something out with my probing and somehow blown the regulator. However the strange thing was that the 5V O/P from the regulator was still up so the rest of the circuit was happy but the regulator started getting very hot (but ultimately it'll still run like this).

OK, I chalked that up to one of those things and that I must have inadvertedly b*ggered something up. I switched to working with the backup board and for a long while everything was fine. I was making some "designer mods" to the circuit - well away from anything regulator - in a prototyping area and when I powered up, this board now has the exact same problem - which tends to imply a fundamental design issue somewhere in my circuit.

The regulator schematic and BOM are WebBench generated (I can post the schematic when I'm back in the office). Input voltages during these tests was around 6V for a 5V O/P.

I haven't had a chance to scope the 5V line when "failed" but a DMM measure of the output shows no shorts or low resistance. When operating normally the TPS62143 doesn't get hot even with currents 500mA, but with a light load and drawing its 200mA it does.

Anything immediately spring to mind with anyone? The end application has a prototyping area for users to add their own customisations so I need something that is robust.

Any thoughts?

 

  • 0
    TI__Guru**** 150790 points

    Typically, drawing excessive current is a sign that the device has failed.  For a switching power supply, board layout is usually the root cause.  Compare your layout to the EVM.  You can also order the EVM to get a known working circuit.

  • 0 in reply to Chris Glaser
    Prodigy 120 points

    It's a two layer board and I followed the recommended layout in the datasheet as closely as possible. If it differs, I believe it to be only to be relatively subtle. Is it really that sensitve to layout that the devices could fail that easily? Is it also overly sensitive to ESD? If so any additional recommendations?

    I'll cross reference it again to both the datasheet and to the EVM (I would have liked to have tried an EVM out prior to prototyping, but they haven't been in stock anywhere for a while).

  • 0 in reply to Jon Watkins
    TI__Guru**** 150790 points

    You can order the TPS62130 EVM in the mean time.  It is just like the 62140 but with a higher current limit.

    All switching power supplies are sensitive to board layout and ESD.  There's nothing special about the TPS62140 in this regard.

    Other common sources of failure include violating the abs max voltage rating of any pin (including when applying a voltage to the output), 'hot-plugging' the input supply such that it overshoots past the abs max rating due to the inductance of the cable, or saturating your inductor due to insufficient current rating of it.

  • 0 in reply to Chris Glaser
    Prodigy 120 points

    Chris,

    Thanks for the pointers. I need to relay out the board anyway for the next revision and there are a few areas I can tweak to get it even closer to the datasheet layout. I'll give that a go and see where we go from there.

    Many thanks for your help

  • 0 in reply to Jon Watkins
    Intellectual 510 points

    Jon, did You find the cause of that problem? Was it really the PCB layout?

    I am also interested because I consider using TPS6214x.

  • 0 in reply to Sergei Vereskov
    Prodigy 120 points

    Sergei,

    I believe that I have, and I think it was the layout. I analysed it again and there were some optimisations I could do. I have now redesigned the board and have not had a failure again in any of my prototype boards. I'm just about to send out a load of Beta boards to testers and if they all survive without this problem again, then I'll be happy it's fixed.

    Jon

  • 0 in reply to Jon Watkins
    Intellectual 510 points

    Jon,

    Was it a real error in the PCB layout or TPS6214x are just very sensitive to the way the layout is done and any step aside from the the reference design ( EVM ) causes such problems?

  • 0 in reply to Sergei Vereskov
    Prodigy 120 points

    It wasn't an error as such, but it didn't follow the EVM layout as closely as I'd first thought. If I remember correctly, some of the capacitors were connected with vias and not close enough to where they needed to be. The point was: I thought I had laid it out well, but in actual fact I hadn't. It was a bit of a "Dog's Breakfast" really.

    I think as long as you follow the EVM layout, you'll be fine. The lesson I've learned here, is that layout is very important for these devices - particularly on 2-layer boards. I think in the past on 4-layer boards I've "got away with it" as they are much more forgiving and hadn't paid close enough attention to it.

    So far, I'm loving this chip. I've given it a good workout in my prototypes and an very happy with it. 

    Jon