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• TI Thinks Resolved

# LMT87-Q1: Junction Temperature

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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