ADXL350 - Non-operation at high temperature

Thank you for posting your question.   I am sorry for the delay in our response, but we will be on holiday until next week.  I will say that this is not a normal behavior, for these devices, so I would start with wondering about the connections or the stability of the power supplies. 

Dear Sir/Madam, 

During several tests, when operated with ADXL350 Power Sequence, it operates normally. (If the main power is turned on first and then the power of the ADXL350 is turned on, it will operate normally, and if the power of the ADXL350 is turned off and on without the register being read, it will operate normally.)

Even if delay is given before ADXL350 control with S/W, if MCU and ADXL350 power are tied up, it still does not work when there is heat.

Thank you, MIKE-NOH , for the additional information.  

Just making sure that I am understanding correctly

1. When you remove the inductors, the "suspect ADXL350" works correctly, even up to 90C
2. When you sequence the power on/off processes, as you describe, you are getting successful results, even up to 70C.

Is this correct? 

When the inductors are installed and you are experiencing problems, how much time are you allowing, from the time power is off and the time that you turn power back on?  

Could you probe the supply voltage, on both working and non-working units, especially in a manner that provides time correlation, with the problematic observations? 

PdelCorro - Feel free to jump in on this. Happy New Year! 

Hi MIKE-NOH and Mark, happy new year! 

MIKE-NOH, I understand the following:

1) you have one device that works properly, even at 70C or more and one that stops working at 40C. Is this correct?

2) Also that when you remove the ferrite beads from the circuit and replace it by a switch, the sensor that was previously not working at 40C now works properly. Is this also correct ? 

I agree with Mark that the inductors/beads might have a loose contact pad or a soldering issue that appears when the PCB expands due to the increase of temperature. And just to be sure I would wait a couple of milliseconds before communicating with the sensor, to allow the low pass filter formed by the inductor and the decoupling capacitor to settle. 

I hope it helps, 

Pablo. 

Dear Pablo, Mark,

Happy New Year!  Thank you for your kindly support. 

1. When you remove the inductors, the "suspect ADXL350" works correctly, even up to 90C

==>It is the same,  if I remove the beads(L7 and L8).  

        2.  When you sequence the power on/off processes, as you describe, you are getting successful results, even up to 70C.

==> Yes,  When ADXL has bad communication, it operates normally when the main power is turned on after the switch is installed.
In addition, when the register is not read and the power of the ADXL is turned off and on, it operates normally.

1) you have one device that works properly, even at 70C or more and one that stops working at 40C. Is this correct?  

==> Yes

2) Also that when you remove the ferrite beads from the circuit and replace it by a switch, the sensor that was previously not working at 40C now works properly. Is this also correct ? 

==> Yes,  Even if delay is given before ADXL control with S/W delay, if MCU and ADXL power are tied up, there is still the same phenomenon when there is heat.

A normal ADXL device that does not show a stopping phenomenon operates normally even when heated above 70 degrees.

Best & Regards,

Hi Mike,

I am not sure why this is happening, but I think is worth to try swapping the sensor from one board that works ok to the one that doesn't to check if it is a board related issue. Could you try that? 

Thanks, 

Pablo.