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Original question:

Powering ADS1262 from 3.6v battery

ADS1262: Powering ADS1262 & loadcell from 3.6v battery

spanky
Expert 2710 points
Part Number: ADS1262
Other Parts Discussed in Thread: TPS60403, LM27762, TPS61220

I'm revisiting this project. I have the ADS1262 working with my loadcell on a 0-5v supply, but would like to run it off a single cell battery.

I found this document:
www.ti.com/.../sbau206a.pdf

It shows +2.5v by a TPS79225, and -2.5v by a TPS72325. Digging further, a TPS60403 gives unregulated negative voltage to the TPS72325.

First question: Is this a power-efficient setup, and sufficiently clean for the voltages to the ADS1262? Or should I go with the suggestion of a LM27762 from the first linked post below, or a TPS61220 to boost the voltage from the 2nd post below?

Second question: Here's my schematic attempting to replicate the TPS72325/TPS79225 from that reference design. Previously I had pin #7 on the ADS1262 tied to the same ground as everything else. Now I'm separating those entirely so VSSA is tied to -2.5v from the TPS72325 and VDDA is tied to +2.5v from the TPS79225. In particular, the loadcell connection is now +/-2.5v from those same sources. Does this look right? I'm still a bit confused with the REFOUT and AINCOM pins, but those seem to work in my existing 0-5v configuration (and are unchanged in this schematic)



Related posts:

https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/873367/ads1262-powering-ads1262-with-a-single-lithium-cell

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/874087/powering-ads1262-from-3-6v-battery

  • 0
    Expert 2710 points

    Some offline comments pointed out my grounds were off a bit relative to the switchover to VSSA. I updated the schematic accordingly:

  • 0 in reply to spanky
    TI__Mastermind 34991 points

    Hi Spanky,

    Here are some comments about your schematic:

    • I would follow the power supply decoupling scheme shown in Figure 11-1 in the ADS1262 datasheet (copied below)
    • It does not seem like you need the ADC's internal reference for any reason. Since this is a battery powered application, it might make sense to turn the internal reference off to save power. If you do this, you do not need to cap between REFOUT and AVSS. You can then tie unused analog inputs (AINCOM, AIN2 - AIN5, AIN8, AIN9) to digital ground (GND, in your case), since this is now mid-supply
    • I did not see how the digital supply voltage (VDD) was generated, or the actual voltage level, so I will assume for now that you have a clean supply for this voltage and that it is within the ADS1262's allowable range.
    • I did not see any resistors on the analog inputs to act as overvoltage protection and filtering. You might consider adding these resistors

    The power solution shown in the ADS1262EVM is adequate for a clean, bipolar supply, though it was not designed with a battery-powered solution in mind. I would defer to the power management team to offer you the best advice regarding an efficient way to generate the +/-2.5V.

    -Bryan

  • 0 in reply to Bryan Lizon86
    Expert 2710 points

    I fixed the decoupling per that diagram (thanks). I grounded REFOUT and the unused AIN's/AINCOM.

    You're correct, I'm not using the internal ref. Was I supposed to ground REFOUT/PIN8, or just leave it unattached?

    I'm supplying the 3.3v with a LM78M33 and that seems to be working (probably not ideal in the battery configuration, but good enough for this phase)

    Do you have an example of the resistors on the AIN's for filtering? I'm less worried about overvoltage since the loadcell is pretty close to the board (at least at this phase)

  • 0 in reply to spanky
    TI__Mastermind 34991 points

    Hi Spanky,

    According to section 9.3.8.1 in the ADS1262 datasheet, the cap from REFOUT to ground is not needed if the internal VREF will not be used.

    The ADS1262 EVM includes the filtering resistors in the EVM schematic. You can also reference this FAQ for more information: https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/955466/faq-delta-sigma-adc-anti-aliasing-filter-component-selection

    -Bryan

  • 0 in reply to Bryan Lizon86
    Expert 2710 points

    So do I ground REFOUT (without the cap), or just leave it unattached

  • 0 in reply to spanky
    TI__Mastermind 34991 points

    Hi Spanky,

    Yes, you can leave REFOUT unconnected in this case

    -Bryan