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Original question:

PGA309's EEPROM programmed flag TI was changed despite of OWD bit is set to 1

PGA309:

Guillaume Longu
Prodigy 150 points
Part Number: PGA309


Hello,

We use the PGA309 for a pressure sensor (prototype). This prototype has been tuned, calibrated and was OK (pressure and temperature). But during endurance tests (temperature/pressure cycles), the sensor failed.

And after investigation, I found a problem in the EEPROM : The first memory adress changed (only one adress). The TI flag 5449 changed to E410. Could you explain me what that ASCII code means ? 

I found a similar topic without answer.

Thanks

Guillaume

  • 0
    TI__Guru 55466 points

    Hi Guillaume,

    After the voltage supply becomes valid, the PGA309 waits a short delay and then attempts to read the configuration registers from the external EEPROM. The PGA309 looks for the correct EEPROM programmed TI flag, and checksum values to ensure the EEPROM is programmed properly.   Therefore the EEPROM must be programmed with the TI flag word 0x5449. This value must be in address locations '0' and '1'.  The code 0x5449 in hex means "TI" in ASCII binary character code table.  (T= 0x54= "084" and I=0x49="073" in ASCII).

    The PGA309 only uses the value 0x5449 on address locations '0' and '1' as the EEPROM programmed flag. No other values, nor information are programmed to this first memory address from the PGA309 side.

    Therefore, a value xE410 does not mean anything from the PGA309 perspective. Is it possible that the EEPROM lost some of its programmed values during the endurance tests? 

    Thank you and Regards,

    Luis Chioye

  • 0 in reply to Luis Chioye
    Prodigy 150 points

    Hi, 

    Thanks for your answer, but that doesn't make me feel confident for my aerospace application.

    I will use the WD pin of the EEPROM to secure the data memory.

    Regards

    Guillaume

  • 0 in reply to Guillaume Longu
    TI__Guru 55466 points

    Hi Guillaume,

    The post mentions that the EEPROM lost the TI flag information during the pressure and temperature endurance cycle tests. I understand devices may be subjected to EMI/RFI or radiation during qualification tests.  Was the EEPROM information lost during pressure/temperature endurance tests or other EMI/RFI qualification tests?  The User guide discusses the recommended EMI/RFI protection to the PRG pin, where noise can be injected in the PRG One-wire interface.  Although the OWD bit (Register 4 [D15]) can be set to '1' to disable the One-wire interface after final programming is completed, there is a 33ms window remains open after power-up where noise can be coupled into the PRG pin and be interpreted as coherent communication.

    Figure 4-21 on the User Guide suggests am EMI/RFI filtering circuit on the PRG pin to help mitigate and reduce the risk of noise being injected on the PRG pin.  However, I agree with you, using the WP pin of the EEPROM will help further eliminate possibility of losing information on the EEPROM.

    Many Thanks and Regards,

    Luis

  • 0 in reply to Luis Chioye
    Prodigy 150 points

    Hi,

    The EEPROM lost the TI flag during pressure/temperature endurance tests only. But we will have to perform EMI tests for qualification. 

    Our pressure sensors are made of stainless steel and hermeticaly sealed by welding, and act as a faraday cage. And the in/out pins are protected against lightning ESD (by TVS) and EMI (EMI filters). The Prog pin is tired to Vcc with a 47K resistor. That s why I am not reassured. 

    I will set OWD to "1" and use the WP pin of the EEPROM.

    Thx

    Guillaume

  • 0 in reply to Guillaume Longu
    TI__Guru 55466 points

    Hi Guillaume,

    Thank you for the clarification, setting OWD to "1" and using the WP pin of the EEPROM should protect the programmed settings.

    Please let us know if you have questions,

    Kind Regards,

    Luis