We are using the LSM6DSRX in a design for underground mining. The approval center asks for the RTH value of the sensor to calculate the max. temperature in any case of failure. Could you pleas send it to me?

[Eleon BORLINI · Accepted solution]

Hi @PRahm.1​ ,

That's an interesting application! If I can ask, are you using this device for (offline) inertial navigation, for vibration patter recognition (for example with the embedded MLC), for predictive maintenance of mining tools or other applications? You can write me a message if these info are confidential.

About the topic, please consider first the "Absolute maximum ratings" table limits in the LSM6DSRX datasheet, p.15:

• Storage temperature range: -40 to +125 °C;
• Operating temperature range: -40 to +85 °C.

Please note also that the sensor temperature and resulting thermal impedance from “junction to sensor�? depend on many conditions that are outside the design of the module itself (board design, cooling system etc...). These conditions influence both lateral temperature spreading and vertical heat conductivity in the system.

In any case, the total thermal junction resistance for the LSM6DSRX is dominated by the package thermal resistance whose average value is 80°C/W: considering a maximum supply voltage of 3.6V and a max current high-resolution mode) of 1.2mA, the power consumed in the worst case is P=V*I=4.32mW. the thermal difference between the device and the environment is DeltaT < 0.5°C.

For this reason the dominant worry about the junction temperature with respect to storage temperature.

You can of course monitor the internal "real-time" sensor temperature using the embedded temperature sensor (described in the datasheet at p.12), to prevent any potential damage of the sensor and of the application.

-Eleon

[PRahm.1]

Hi Eleon,

we will use the Sensor at first as angel meter. The roof supports used underground have - with simple words – three steel plates which are moved up and down by a lot of cylinders. So we are measuring the location of the three plates and can than calculate the actual hight of the supports. On top we will use them to measure vibrations.

The norm for intrinsically safety DIN EN 60079-11 says that a semiconductor might have any failure. That means on each pin might occur an internal shortcut to any other pin. In this case the complete power of the power supply (in our case 3.4W) could be transferred to the chip. And if so the max. temperature must be below 450°C. Any internal temperature sensors are not seen as a safety feature.

That’s why we need the thermal resistance of the sensor.

[Eleon BORLINI]

Hi Peter,

Thank you for the details of your (interesting) application.

Considering a thermal resistance for the device package (from the outer environment to the inner silicon) of 80°C/W, the calculation with 3.4W leads to a max temperature of 272°C < 450°C, so your specification should be met.

Let me please know in case you need further help.

-Eleon

[PRahm.1]

Hi Eleon,

That’s great. Do you have any official pater where is written the 80°C/W? The approval center always likes some paperwork what they can add to the approval file.

That would be fine. In the meantime we will go on with your information.

Thank you very much.

[Eleon BORLINI]

Hi Peter @PRahm.1​ ,

I'm checking internally for the document, even if it is very unlikely to face this problem, as above described...

Meanwhile I can attach you the material declaration form for the LSM6DSR, if can be of any utility for you

-Eleon

[Eleon BORLINI]

Hi Peter,

back to you with a document for RTH. It's not an official document, in the sense that it has never been published online as a Technical Note (TN), but it has been shared several time to the customers. It contains an estimation of this quantity required for different packages.

I'll share it with you in the message section for confidentiality.

If it's ok, we could close this thread.

-Eleon

[PRahm.1]

Hi Eleon,

thank you for your help. Sounds good and that should be ok. The only thing is that I can't see the paper you mentioned. Is it possible to share it with me - either here or by Email.

That would be graet.

Peter

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