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TPS61202 Runaway Protection

Other Parts Discussed in Thread: TPS61202

I'm working on a new design using the TPS61202 to boost a 3.7v Lipo to 5v.  The circuit seems to work great with a lipo cell, but I had one very odd and dramatic failure that has me worried.  I was trying to get a more precise measurement of active current use in a typical use case and was powering the prototype from a bench power supply set at 3.7 volts with a current limit of 1A.  The bench supply indicated the test was drawing about 200 mA but, as the current meter in the bench power supply was only 2 fractional digits, I added in a multimeter to get a more precise measurement.  The minute I connected the multimeter  the power draw jumped to 1A and TPS61202 got very hot.  I disconnected the bench supply and reconnected the lipo, but the chip and the battery started to get quite hot, so I disconnected the lipo.  All subsequent test indicated the TPS61202 was dead.  I unsoldered the old part and put in a replacement and the prototype began working again.  But, now I'm spooked about using the TPS61202 in this design without some sort of external over-current protection, such as a fuse, or a PTC.  However, the design notes don't coverr this, so I wonder what would be a OK to use something like a PTC in series with the battery input to the the TPS61202.  I'

  • personally, we should found why the device fails first.for lipo powe supply, efficiency will be a big concern, resistor in series will reduce the efficiency significantly. can you repeat the phenomena with the new part?
  • I've had a second failure but, this time, the trigger seems to have been that the connected, 3.7 v lipo battery discharged below the 2.7 volt shutoff point I set using values for R3 and R4 connected to UVLO.  After the battery was recharged and reconnected, the same type of high current daw, thermal runaway happened and the TPS61202 now gets red hot whenever a lipo is connected (regardless of the state of the EN pin.)  Here are the details on how I have the TPS61202 configured:

    The EN (enable) line is used to turn the TPS61202 on and off by means of a slide switch used to select between GND and the Lipo input.  I have 10uF, low ESR caps very closely connected to the input and output terminals.  Thermal vias connect the chip's thermal pad to the ground plane on the 2nd layer.  There's a .1 cap on the VAUX pin.  R3 is 2.1 Meg and R4 is 232K and this divider connects to UVLO (I also added a .1uF cap from VIN to UVLO.)  The PS pin is connected to GND to enable power save mode.  The FB pin is connected to VOUT for 5 volts output.  L1 is a Coilcraft LPS3015-222MRB.  

    When it works, the TPS61202 is a great part and lets me get a lot of power out of a small amount of PCB space.  However, I just can't have these kinds of high current failures in a finished design, as they could easily lead to a fire.  So, I'm hoping you can help me figure out why this is happening.

    Wayne

  • hi wayne,

    the information is not enough for us to judge what the probelem is.have tried replace the lipo battery with a DC power supply? can you email me a0222798@ti.com for our support? we can't see the thermal issue on our EVM ,so you need to post your schematic and layout, input and output conditions for us to analysis.

    Charles
  • I sent an email to a0222798@ti.com on Monday, May 25 with diagrams and both details.  Did you receive it?

    Wayne

  • Did you ever get a response from this?  I've found something similar - noticed some form of thermal runaway and 1.2A drawn when ammeter connected in series on occasion.  Now  one of the chips has died completely.  My chip now shows a short circuit in the TPS621202 itself between input and ground (I'm assuming it's on the chip - using a pololu daughter board U1V11F5 which is based on this chip to prototype this.)


    There's an interesting note at the end of Pololu's product page about LC spikes and as connecting an ammeter in would certainly add some series inductance I wonder whether this is enough to cause problems as the chip has relatively low max Vin.  Also pretty sure when I blew the chip there was a loose battery wire and/or I had it connected to a battery pack with   a higher than normal voltage (I'm only running around 2.4V Vin (2xAAA nimh) but had tried tests whilst connected to 3xAA alkalines which might have got to around 4.5-5v which perhaps exacerbated the issue if this was due to an LC spike.

    Is there anyone on TI that can comment on this and if in particular the failure mode I'm experiencing (shorted Vin to gnd) might be expected in a condition of a spike going over the max Vin?  It's a bit hard for me to see if the short is really between these pins without pulling all of the SMD components off the daughter board - it could conceivably be an internal short between any two pins connected to Vin and Gnd on their daughterboard (schematic here: )

  • Hi Tom
    solder the TPS61202 out the PCB and check the VIN and GND again. if the failure is caused by the TPS61202, please share the image of your PCB, which could also cause damage if it is not good.

    high input voltage could also be the root cause. you can replace with a new device and repeat the experiment again. try to capture the VIN waveform this time.
  • Your experience parallels mine.  I did discuss this with a TI engineer, but I was unsatisfied with the result and decided to switch to a different design and regulator IC.  I do think there is an issue that, while perhaps workable in some designs, can result in a shorted part when the the input power source is abruptly interrupted, such as when trying to connected a meter in series to measure current draw (or perhaps due to some inductance in the meter.)

    Wayne