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ADS1198: ADS1198

Vladimir Gomon
Prodigy 30 points
Part Number: ADS1198

Tool/software:

Hi! Would you please explain how to use LOFF_FLIP?
For example:
RA connected to the IN1P,
LOFF = 0xEF
LOFF_SENSN = 0x00
LOFF_SENSP = 0x01
LOFF_FLIP = 0x00
Works perfect, when RA is off, I read LOFF_STATP = 0x01 

If I set
LOFF_FLIP = 0x01
with intention to "draw" RA to GND instead of AVDD:
0. Should I still activate RA (IN1P) lead detection by setting the bit in LOFF_SENSP, not in LOFF_SENSN?
1. Where am I supposed to read the result?  In LOFF_STATP or in LOFF_STATN?
2. Which comparator will be used: "positive" which activates if RA potential is above 70% of AVDD or "negative" which activates if RA potential is below 30% of AVDD?
3. Does LOFF_FLIP do flip for current sources and for pull-up/down resistors both?

I am asking because if FLIP option does nothing except switching current source and all logics remains the same, so I do not understand its sense. Pulling "down" the positive potential will never result in "positive" comparator activation, right? Or I do not understand something. Would you please explain?

  • 0
    TI__Guru 66346 points

    Hello Vladimir,

    The LOFF_FLIP bit controls both the excitation source (resistor and current pull-up/down) as well as the comparators. So, in your example, if LOFF_FLIP is enabled for IN1P, then the pin will be connected to the current sink/resistor pull-down, and the comparator will monitor for the low-voltage threshold (i.e. < 30% AVDD).

    I believe the LOFF_SENSx enable bits and the LOFF_STATx results stay associated with the same register (LOFF_SENSP[0] and LOFF_STATP[0] for IN1P). Let me know if you need to me to test and confirm the same.

    Regards,

    Ryan

  • 0 in reply to Ryan Andrews
    Prodigy 30 points

    Hi Ryan. At the beginning, I assumed that the FLIP option works exactly in the way you suggested, it sounds quite naturally.
    I assigned LOFF_SENSP = 0x01, LOFF_SENSN = 0x00 but I did not get LOFF_STATP = 0x01 (I mean bit [0:0] only) when IN1P was OFF, I see it is ON always. 
    So would you please confirm how FLIP works?
    Regards

    Vladimir

  • 0 in reply to Vladimir Gomon
    TI__Guru 66346 points

    Thanks, Vladimir. I will look into this today and confirm the behavior.

    Regards,

    Ryan

  • 0 in reply to Ryan Andrews
    TI__Guru 66346 points

    Hi Vladimir,

    I can confirm that the LOFF_FLIP bits flip the direction of the lead-off current and swap the corresponding lead-off comparators. However, the comparator outputs remain associated with the same lead-off status registers as before. This means that comparators monitoring for high-voltage thresholds always report to LOFF_STATP and comparators monitoring for low-voltage thresholds always report to LOFF_STATN. The LOFF_SENSP and LOFF_SENSN bits stay with the associated pins. 

    To give an example, say you want to enable DC lead-off on IN1P:

    When LOFF_FLIP[0] = 0b:

    • LOFF_SENSP[0] = 1b connects the resistor pull-up or current source to IN1P (pulls up to AVDD when pin is floating)
    • Comparator monitors for high-voltage threshold (i.e. 90% of AVDD)
    • Comparator output is read through LOFF_STATP[0] for IN1P status

    When LOFF_FLIP[0] = 1b:

    • LOFF_SENSP[0] = 1b connects the resistor pull-down or current sink to IN1P (pulls down to AVSS when pin is floating)
    • Comparator monitors for low-voltage threshold (i.e. 10% of AVDD)
    • Comparator output is read through LOFF_STATN[0] for IN1P status

    Hope this helps!

    Regards,

    Ryan