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LMP90100: Use multichannel mode with burnout currents

Naman Kumar
Intellectual 430 points
Part Number: LMP90100
Other Parts Discussed in Thread: ADS124S08, ADS1248,

I want to use multichannel scan along with diagnostic flags. I am getting signal from a strain gauge and checked the ADC data and flags in 2 modes i.e.

ScanMode2: One or more channels Continuous Scan
ScanMode3: One or more channels Continuous Scan with Burnout Currents

1. In both cases, i could get the flag status changing. Rail Flags set when I disconnect the transducer in both modes.  Then what is the significance of ScanMode3 (with burnout curents)?

2. When would SHORT_THLD_ FLAG be set if I have not set SENDIAG_THLDH and SENDIAG_THLDL values? I can see it setting when the input signal voltage is very high but less than VA. e.g. With VREF and VA set at 5V, and gain 128, OFLO flag sets at 39mv and SHORT_THLD_ FLAG sets at 1.3V.

3. When does POR_AFT_LST_RD flag get set and what is its significance? The datasheet says : Power-on-reset after last read = 1 when there was a power-on-reset event because the last time the SENDIAG_FLAGS register was read. But why would the ADC reset after a read?

Regards,


Naman

  • 0
    TI__Mastermind 49381 points
    Hi Naman,

    Thanks for your post! Is this for a new design? If so, I highly recommend considering the ADS1248 or ADS124S08 family of devices.

    I'm not very familiar with this device so I'm reaching out to a colleague of mine to confirm my answers.

    1. ScanMode3 is the only mode that scans multiple channels while injecting burnout currents without interfering with the signal. This is described in detail in the Burnout Currents section.

    2. I do not see default register values for SENDIAG_THLDH and SENDIAG_THLDL in the datasheet, however looking at the example in section 9.3.8.3.1, your observation makes sense. When (-38.2mV) ≤ VOUT ≤ (38.2mV)

    3. "Power-on-reset after last read = 1 when there was a power-on-reset event because the last time the SENDIAG_FLAGS register was read."
    I believe this is trying to say that the flag gets set when there is a power on reset event (such as the power supplies dropping) since the last time the register was read.
  • 0 in reply to Alexander Smith
    Intellectual 430 points
    Hi Alex,

    Thanks for the reply. Yes, this is a new design. I see ADS1248 or ADS124S08 are very recent converters by TI. I will take a look at these. Could you tell me more about them. We would be using 4 channels for conversion of signals by strain gauges connected at each channel. We do not need speed of more than 5 sps for each channel. Also please let me know if TI would discontinue the supply of lmp90100 in near future?

    Regards,
    Naman
  • 0 in reply to Naman Kumar
    TI__Mastermind 49381 points

    Hi Naman,

    First and foremost, the price is lower for both devices and the ADS124S08 VQFN is the smallest size. The DC performance is better and the noise is lower for both devices. The ADS124S08 is our newest device; as such it represents the best of our technical capabilities and has a plethora of integrated features. There is also more supporting documentation for the ADS124S08. I ask you to strongly consider the ADS124S08 as it is the best we have to offer.

    Currently, there is not an active plan to discontinue supply of the LMP90100. However, since it is the oldest of the 3 devices, I would speculate that the newer devices will last longer.

    TI does not have any longevity programs or make statements on how long a device's manufacturing lifetime may be. Here is a quote from a document located at www.ti.com/quality It is in the General Quality Guidelines document.

    TI’s Product withdrawal/discontinuance process complies with J-STD-048, latest issue. TI makes an effort to not obsolete products out of convenience. Convenience means: low running device, poor yields, limited customer adoption or similar items. TI’s obsolescence withdrawal schedule provides a longer lead time than the industry standard. TI allows 12 months for the last order and an additional 6 months to take final delivery of obsolete items. In rare circumstances, an accelerated withdrawal schedule may be necessary. In such cases, TI will communicate the last buy and final delivery dates in the EOL notice, along with an explanation of the circumstances necessitating the early withdrawal.