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LM7301: About LM7301 Max Tj

Vera Mao
Expert 5065 points
Part Number: LM7301

hi dear supporting team,

how about the max operating Tj of LM7301?  from 85degree TA, it seems Tj could not exceed 100 degree. customer is operating at 8V, they normally get 96degree case temp. and the highest case temp could get to 110degree. is it ok? tks a lot!

  • 0
    TI__Mastermind 30600 points
    Hi Vera,

    Table 6.1 in the datasheet shows that the absolute maximum for the junction temperature is 150° C. As long as the ambient temperature is 85° C or less (staying inside the recommended operating range) then the device will perform with the datasheet specifications.

    Best,
    Paul
  • 0 in reply to Paul Goedeke
    TI__Expert 5065 points

    hi Paul,

    tks for reply!

    because it is in the power module, they are hard to measure the ambient temp, the only temp they could measure is the case temp.  so for 110degree case temp, is it over the operating range？ tks!

  • 0 in reply to Vera Mao
    TI__Mastermind 30600 points

    Hi Vera,

    Take a look at the TIPL video on temp and power: training.ti.com/ti-precision-labs-op-amps

    In this case, the equation used would be: Tj = Pd*(Theta_JC)+Tc

    Just accounting for the quiescent current of the device at 8V supply of 0.6mA for Pd, the junction temperature with a case temp of 110° C would be:

    DBV Package: (0.6mA)(8V)(122 °C/W)+110°C = 110.6° C
    SOIC Package: (0.6mA)(8V)(65 °C/W)+110°C = 110.3° C

    If the output voltage is known, you should add that to the power dissipation of the op-amp. To violate the absolute maximum with a 110°C case temperature, the circuit would need to be dissipating 327mW in the DBV package or 615mW in the SOIC package.

    Hope that helps,
    Paul

  • 0 in reply to Paul Goedeke
    TI__Expert 5065 points

    Hi Paul,

    yes, I know that equation.  my question is： what's the max Tj for normal operation without violate the d/s spec?  for 150degree, it is Tj that without destroy the chip, but if approach to 150degree, the spec should be degraded a lot.  isn't it? 

  • 0 in reply to Vera Mao
    TI__Mastermind 30600 points
    Yes, performance and lifetime will be impacted as you increase closer to the abs max Tj.

    We qualify our devices by looking at the ambient temperature and making sure that the power dissipation of the device does not exceed the abs max for Tj (150° C for the LM7301). It is difficult to accurately measure the Tj directly so we can't provide a specified value for Tj, just an abs max.

    At 110° C case temperature, it is likely that the Tj is already elevated above what Tj would be in an 85° ambient temp.
  • 0 in reply to Paul Goedeke
    TI__Expert 5065 points
    Hi Paul,
    I rechecked the d/s , for highest power consumption calculation, 32V, the total current could (Is+Isc)=11.7+1.35=13.05mA. then the max power consumption will be 0.417W, then the Tj will be 85+0.417*169=155degree.
    is the calculation ok? if yes, then could we say customer's application is ok? because this is 5G project, customer could not change the solution now, they have use this solution for long time and have no issue till now. so they want to prove it is safe to go ahead. tks a lot!
  • 0 in reply to Vera Mao
    TI__Mastermind 30600 points
    Hi Vera,

    Because the customer can only accurately measure the case temperature, I think it would be better to calculate what the maximum allowable case temperature would be for the maximum power consumption:

    SOIC:
    Tj = Tc + (R_ThetaJC)*(Supply Voltage)*(Isc_max + Iq_max)
    150C = Tc + 65*(32)*(1.35mA+11.7mA) --> Tc_max = 122.9° C

    DBV:
    Tj = Tc + (R_ThetaJC)*(Supply Voltage)*(Isc_max + Iq_max)
    150C = Tc + 122*(32)*(1.35mA+11.7mA) --> Tc_max = 99.1° C

    I hope that helps,
    Paul
  • 0 in reply to Paul Goedeke
    TI__Expert 5065 points

    Hi Paul,

    In this calculation, you still use 150 degree which is the absolute rating. But If use my calculation, it seems the operating TJ could get to 155degree. Could you double check that with 150 TJ the chip could work within the d/a spec? Tks!

  • 0 in reply to Vera Mao
    TI__Mastermind 30600 points
    Hi Vera,

    With the short circuit current at the maximum ambient temperature, it is possible to overheat the device. Look at note (3) under Table 6.1:

    "(3) Applies to both single-supply and split-supply operation. Continuous short-circuit operation at elevated ambient temperature can result in
    exceeding the maximum allowed junction temperature of 150°C"

    Best,
    Paul
  • 0 in reply to Paul Goedeke
    TI__Expert 5065 points

    Hi Paul,

    so if customer only operate at 8V, if they get 96 degree case temp for normal, and max case temp will go to 110degree. will this violate the operating rating? I am wondering could we use 150degree as the operating temp.  tks! 

  • 0 in reply to Vera Mao
    TI__Mastermind 30600 points
    150C is an allowed operating temperature, but it is the absolute maximum so the device will have performance impact and reduced lifetime. To stay within the datasheet specifications, the ambient temperature needs to be 85C or less.

    With only 8V supply and a reasonable 5mA output current, it seems unlikely that Tj will be very different than the case temperature:
    Tj = Tc + (R_ThetaJC)*(Supply Voltage)*(Isc_max + Iq_max)
    96 + 65*(8)*(5mA+1.35mA) --> Tj = 99.3° C
    110 + 65*(8)*(5mA+1.35mA) --> Tj = 113.3° C

    In this scenario, the case temperature is a good approximation for the junction temperature. If they know their maximum output current, they can estimate well.

    -Paul