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LM211: lm211

kerry querns
Prodigy 120 points

Part Number: LM211
Other Parts Discussed in Thread: LM111

We're using LM211 in a new design.  Table in section 6.1 says the operating virtual junction temperature is 150C, but goes on to say it's a stress rating only and that functional operation at these or any other condition beyond is not implied.  So kind of useless except as a damage limit.  Table in section 6.3 give ambient temperatures only (-40 to 85C for LM211 and -40 to 125C for LM211Q).  Can you please provide a maximum operating junction temperatures at which functional operation per datasheet is guaranteed?  Our aerospace environments often exceed 85C.  We base limits on junction temperatures since that is more indicative of a parts capability.

  • 0
    TI__Mastermind 19850 points

    Hi,

    We have acknowledged your post and will get back to you by the end of business tomorrow 10/14.

    Thanks,

    Joe

  • 0
    TI__Mastermind 19850 points

    Hi,

    The functional operation of the device is warrantied at an ambient temperature range of -40C to 85C. The junction temperature of the device is actually higher than 85C when tested at an ambient temperature of 85C (due to self-heating). You can use table 6.4 in the datasheet to calculate the junction temperature at 85C ambient.

    Operating in the temperature range of 85C to 150C may impact reliability and performance of the device. We encourage operating the device below this range. I hope this answers your question and feel free to reach out to ask any additional questions.

    Thanks,

    Joe

  • 0 in reply to Joe Vanacore
    Prodigy 120 points

    Nope, this doesn't answer my questions.  Table 6.4 only helps if I know the maximum allowable power dissipation at that 85C limit, assuming JA*Pdmax +85C.  Can you provide Pdmax at 85C?  I'm not an ED guy  so I'm not sure how to figure this out.

    To clarify a bit, junction temperature is the parameter which limits a parts operational capability. Not ambient temperature.  Vendors got away from providing junction limits some 15 or 20 years ago, probably to save money..  But to properly say whether a part can operate even at 85C you need to know at what power.  Often we don't dissipate the allowable power at 85C, and even more often in aerospace our environments exceed 85C  so we want to know if the part will still function.  So far as reliability goes, again that's a function of the junction temperature over time (somewhat cumulative).  While reliability is impacted as junction temperatures increase above 85C, generally we're not at the high temperatures for extended periods so it's not an issue. 

  • 0 in reply to kerry querns
    TI__Mastermind 19850 points

    Hi Kerry,

    The LM211 should still function as a comparator at 150°C, but it will not meet the specified temperature range performance (ie; Supply current, input bias current, output drive, prop delay specs). You need to greatly widen the design tolerances if you expect operation at the temperature extreme.

    Technically, there is no margin for more power dissipation at 85C to meet specs. As I eluded to, during testing, the actual die temp is higher than 85C due to the devices own power dissipation (plus any specified load power dissipation), but that is taken into the specification limits.

    So how much extra power can you dissipate at 85C to hit the 150C limit?

    Remember that power dissipation creates a rise in temperature over ambient.

    150 - 85 = 65°C rise

    You did not specify which package you are using, so we will use the worst case PW TSSOP package at 162 °C/W

    65 / 162 = 401mW

    So you can dissipate a maximum of 400mW at 85C to hit the 150C die temperature limit.

    Assuming a full supply voltage and max supply current, the LM211 itself will dissipate 13.5mA * 30V = 400mW...Uh, oh...

    400mW * 162 = 65C rise...so in the TSSOP package, the margin is already used-up by the self power dissipation. Which is most likely why the LM211Q is not available in the TSSOP package.

    So if you need to dissipate power at 85C, then best to use the DIP package, and use as little supply voltage as possible to minimize self-dissipation.

    Aerospace applications should really be using the LM111..

    Of course, TI recommends staying within the specified temperature range and any operation outside this range is at the customers own risk.

    Thanks,

    Joe