LMP91300: Temperature issues seen during development of a new board

Hello,

Thanks for the post. We will wait for the schematics and until then we will look into the plots and get back to you early next week (Tuesday) with some analysis and further questions...  

Arjun,

Thanks for getting back to me. I am looking forward to working with you to resolve the issues I am seeing.  On failure scenario 2 where the output changed state when in the near mode (target present) indicating the target temporarily was not present but it was, I noticed the Rp value never changed it was always 80 00 as seen in the plots. Is 80 00 the maximum Rp value? We had the target basically sitting on the proximity sensors.

Thanks,

Craig LaBarre

Hi Craig,

The maximum R_p value for the LMP91300 is 3.93 MΩ (section 6.5 – Electrical Characteristics).

I have a few additional questions in order to get a better idea of the issues you are seeing:

• What were the programming steps followed (section 7.5.1)? If possible, please attach a logic analyzer capture of the read/write operations.
• Were the devices functioning as expected at 25°C?
• Is this issue being seen on all units?

Thank you for your continued patience.

Best regards,

Nicole

 Nicole,

Hope you are doing well. I appreciate your help

We just used the first programming step in section 7.5.1 (Burning Programmed Values Into The Registers).

Failure Scenario 3: We saw an issue during hot temperature cycling. One out of four proximity sensors had the thermal register and Rp register value drop to nothing at the same time and never recovered until the proximity sensor was power cycled. We only saw this failure in the near mode (target present). Failure occurred at approximately 70C, within the operating temperature range of the LMP91300NHZ. The failure did not occur every hot temperature cycle. Please see attachment. I looked at the SWIF interface, with a scope, of the failed proximity sensor and there was no data versus the SWIF interface of passed proximity sensors that had data.

We never saw any failures at ambient (25C) during cold temperature cycling and during hot temperature cycling, illustrated in the plots.

For each of the failure scenarios (1-3), not all the proximity sensors failed.

During a read of registers are they modulating the current by bringing the LED pin (terminal) to ground?

Hi Craig,

The LMP91300 modulates the supply current by sinking current into the LED terminal. The V+/EXT and LED terminals need to be connected by an LED, resistor, or directly shorted for the Read operation to take place (section 7.5.2.2).

Thank you for the additional details. What is the proximity of the external temperature sensor to the LC circuit? It is possible that if this temperature sensor is not placed closely enough to the LC circuit there could be exaggerated errors due to temperature variation.

Best regards,

Nicole

Nicole,

Please see attachment, E2E Correspondence_2.E2E Correspondence_2.docx

Thanks,

Craig

Hi Craig,

Thank you for the detailed attachment. While I review your simulation, I think it may be best to move this thread to email. I've sent you a connection request to begin that process.

Best regards,

Nicole