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  • TI Thinks Resolved

LMT87-Q1: Junction Temperature

Intellectual 335 points

Replies: 5

Views: 791

Part Number: LMT87-Q1

Hi there,

I'm calculating the thermal characteristics of LMT87QDCKTQ1 and found the equation below in the datasheet (page 11):

Tj = Ta + Tja.[(Vdd.Is) + (Vdd - Vout ).IL]

 In the same page below the equation, there's an example where the parameters are: Ta = 30°C, Vdd = 5 V, Is = 5.4 μA, Vout = 2231 mV, and IL= 2 μA.

Then the result for the junction temperature in the given example is 30.014°C. Which thermal resistance junction to ambient is being used to achieve this value?

Ps.: In page 6 of the datasheet, the values for Rth,j-a are 275 °C/W (5 pins) and 167 °C/W (3 pins) but both don't match the mentioned result if applied to the used example.

Regards,

João Figueiredo

  • Hi João,

    I need to investigate this, and get back to you.

    Aaron

  • In reply to Aaron Heng:

    Hi Aaron,

    Ok, thanks for the reply.
    Please let me know when you have any update about this topic.

    Regards,

    João Figueiredo

  • In reply to Aaron Heng:

    Hi Aaron,

    Could you check this issue?

    Regards,

    João Figueiredo

  • In reply to Joao Figueiredo:

    Joao,

    I believe this is an error in the datasheet.

    Oja=275;
    Vdd=5;
    Is=5.4*10^-6;
    Vo=2.231;
    Il=2*10^-6;
    Ta=30;
    Tj=Ta+Oja*(Vdd*Is+(Vdd-Vo)*Il)

    Tj should be 30.0089 degC not 30.014 degC. In either case, as you can tell, the self-heating contribution is negligible
    when you consider that the accuracy of the device is 2.7 degC over the entire operating temperature range.
  • In reply to Kelvin Le THS:

    Hi Kelvin,

    Thanks for the reply.
    Ok, I would just like to confirm it.

    Regards,

    João Figueiredo

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