• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 1 answer
  • Subscribers 50 subscribers
  • Views 218 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TLV1701: Part failing and overheating

Thomas Prentice
Prodigy 20 points
Part Number: TLV1701
Other Parts Discussed in Thread: TL331B, TLV1805

Background:

We are using the TLV1701AIDBVT comparator in conjunction with a pull-up to drive the gate of a fast FET. When the + input goes higher than the threshold on the - input, the output turns off, and the FET gate is turned on by the pull-up (1K to 12V, so 12mA). Pulse widths are typically on the order of 50µs. We are seeing many parts (in fact, a majority of units) that are not holding the FET off and they are getting very hot. We replace the part and the circuit works fine.

Question:

Is there something we may be doing to this part that would result in the failure mechanism as I have described it? ESD? Overheating during reflow?

  • 0
    TI__Genius 10415 points

    Hi Thomas,

    We have acknowledged your post and we will respond with more information by end of business day tomorrow (9/25).

    Thanks,

    Joe

  • 0 in reply to Joe Vanacore
    TI__Mastermind 23395 points

    Thomas

    We’ll study this further in the morning as Joe noted but one thing to be aware of is that the tlv1701 has a weaker than average output stage. So when the output of the comparator is pulled low, the output stage may be saturated and could be getting damaged. As you mentioned, the comparator doesn’t actively pull high but when it’s pulling low all of that current is going into the comparator output transistor. If you look at the output sinking current versus output voltage curve you can see how much power is being dissipated.

    Chuck  

  • 0 in reply to Chuck Sins
    TI__Mastermind 23395 points

    You mentioned that the pull-up voltage is 12v but what is the supply voltage for the comparator.

  • 0 in reply to Chuck Sins
    Prodigy 20 points

    The supply is also tied to 12v.

  • 0 in reply to Thomas Prentice
    TI__Mastermind 23395 points

    Thomas

    As I mentioned previously, the output stage on the TLV1701 is not well suited for sinking 12mA.  With a supply of 12V, the drop across the open collector output device with 12mA may be high enough to keep the FET on.  What is the threshold of the external FET to turn it ON?

    Unfortunately Figure 4. Output Voltage vs Output Current only covers the extreme supplies of 36V and 2.2V.  Note that at 2.2V, sinking current of 12mA is close to saturating the output.  By saturation, I mean that the comparator output rises up to the pullup voltage even though the output transistor is turned ON.  

    At 36V, with VCE voltage with 12mA is typically 2V (probably higher than you are expecting).

    At 12V, the VCE voltage is probably even higher.  So that is probably why the part is getting hot and causing the circuit to fail.

    TLV1701 is unique because it is a high voltage device with rail to rail input.  Is that needed in your design?  If not, the TL331B has better sink current capability but this device has a different footprint.  Another option is our TLV1805 which has a push pull output stage and is well suited for driving MOSFETs.  This device would also eliminate the constant 12mA drain when the FET is held off, so this is probably the best option.

    Sorry for providing different options but these are devices I would have recommended if you were starting your design.

    Chuck

  • 0 in reply to Chuck Sins
    TI__Genius 10415 points

    Hi Thomas,

    I am assuming that we have answered your questions so I will close this thread. If you have further questions, please reply to this thread or open another one.

    Thanks,

    Joe