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LM317L-N: LM317L-N

Part Number: LM317L-N
Other Parts Discussed in Thread: LM317

Hi TI,

 I have a few question in relation to the mentioned device.

  • I would like to know the Junction-to-case thermal resistance - But I can only find the JUnction-to-ambient information. Can you tell me the Junction-to-case thermal resistance.
  • Regarding the internal temperature shutdown - at which temperature does is kick in?
  • Is theer a maximum periode of time where it's "allowed" to let the device stay in temperature protection state(eg. during a short).
  • Does a long duration(eg. days/weeks) with the temperature shutdown function active, reduce or degrade the life-time?

Br.

Michael

  • HI Michael,

    Here are the thermal Details I could pull-up for the 8-pin SOIC:

    As for the thermal shutdown temperature, I would have to see if we can get the actual numbers for this device, but it is usually around 165C.

    There is no effective time limit on the over-current/over-temperature protection. the device folds back the current to protect itself. If you mean a short is maintained across the device for an extended period of time, this may impact long-term reliability. So if the short is present for days or weeks, it is likely that the device will suffer some degradation. 

    I hope this answers your questions.

  • Hi John,

    Thanks for the quick response to my questions. I now have a few additional questions.

    • When I look in the latest Datashet which I can find ( SNVS775L ) I see that the thermal to ambient resistance is somewhat higher ( 165°C Vs. "your" 138.9°C ). But ufortunately only junction to Ambient is stated - så that's the reason for my question. So could you please verify/double check that the 66°C is valid for Junction to Case.
    • In relation to the above, then I'm calculating Junction in a specific error state to be around 175°C on junction without the temperature shutdown kicking in. Is that due to tolerances or something else? Please comment
    • I use the LM317 in a current limiter applikation(24Vdc output limited to 50mA). Would you recommend using that trim when the circuit should be able to withstand that the output is directly shorted to GND? The device is in an ambient of around 60°C, and with +1W powerloss in the device, then that could cause well above 150°C on junction. But only 125°C in junction is stated to be OK. But on the other hand the temp. protection is kicking in at around 165°C. Please comment if you think it's OK.

    Thanks...

    Br. Michael

  • Hi Michael, 

    The number for TJA provided is based on a JEDEC standard High-K board. We should have updated the datasheet after getting the more complete thermal data. I can double-check with the packaging team on the results, but these are usually very accurate. The datasheet does need to be updated with the complete thermal picture, but that will take some time.

    Your calculation seems about right. 165 is typical but it is not uncommon to see it as high as 175. This is not an extremely precise threshold.

    If there is a high probability of the output being shorted to GND often and for extended periods of time, you may want to see if there is a means to shut down the power. We do have a newer device (i.e. released in 2011) the TPS7A16 which is a 60V tolerant 100mA LDO with both enable and power-good (PG). The PG signal could be used to cut-power or temporarily disable the device.

    I would be curious to hear your thoughts on this.

    Regards,

  • HI John,

    Thanks for you fast reply. I have been looking at the suggested device - but it seems to have a to low output voltage for my purpose.
    Maybe it makes sense to start "from the begining" and descripe what I'm actually looking for. So here below is a description which I hope clarifies what I'm looking for.

    For a 24Vdc output voltage (eg. For Sensors), I’m searching for a device which can limit the current during a short(error in the wiring in the field). I have been searching TI’s webpage, but I can’t find anything that really seems to fit.

    Here below is some more details.

     

    Input Voltage: Ideally from app. 3V and up to 30Vdc.

    Output current: Able to be adjusted/limited to 40..100mA.

    Voltage drop across device:   <300mV @ 50mA load.

    Temprange:                                 -40°C to 125°C

     

    Enable signal is needed – “Power good” signal would be nice.

     

    I have considered misc. loadswitches but can’t find anything. I have considered misc. LDO linear regulators but can’t find anything either. I have a working desing based on a simple LM317 coupled as a current-limiter, but that solution suffers from to high voltage drop, and the lack of Enable pin.

     

    Hope you can suggest a suitable part. And if you have something “close” to the specifications please let me know anyway.

     

    Best Regards

    Michael

  • Hi Michael,

    Let me know if you think the LP2951-N can work for you. The current limit is not as tight as you would like, but the /ERROR function can let you know a short is present. 

    Regards,