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Original question:

ADS1261EVM: ADS1260 : Need to measure uA current ADC solution

ADS1260: ADS1260 : Need to measure uA current ADC solution_circuit

Jax Yang
Prodigy 50 points
Part Number: ADS1260
Other Parts Discussed in Thread: TPS7A20, TPS61099, REF6025, TPS784, TPS63700, TPS7A30

Hi Team,

Thank you for suggestion.

After discussion of ADS1260’s ability, it could meet/approach our requirement.

Now I have some questions of power management and design:
Mother Board: MCU and Main power-DC5V

Daughterboard: ADS1260

Power Input: DC5V/GND from motherboard of USB/AC-DC5V Adaptor (4.5V-5.5V).
→It takes risk that DC5V will under 4.75V

By the description of ADS1260_P80, it came to us some ideas for stable AVDD/AVSS:

  1. Unipolar
    (1)AVDD:
    Use boost IC to level up DC5V to 5.5V, and then buck it by LDO.
    USB adaptor(4.5V~5.5V) → TPS61099(5.5V output) →TPS7A20 (5V output).
    (2)AVSS = GND.
    (3)VREF: REF6025(2.5V)
    I get the results as bellow: (PASS)
  2. Bipolar:
    (1)AVDD:
    Use LDO to buck the DC5V.
    USB adaptor(4.5V~5.5V) → TPS784 (+2.5V output)

    (2)AVSS:
    Use negative voltage output LDO to inverter DC5V, and then buck it by negative LDO.
    USB adaptor(4.5V~5.5V)     → TPS63700 (~-4V) → TPS7A30 (-2.5V output).
    (3)VREF: REF6025(2.5V)
    I get the results as bellow    : (FAIL) - because of the VIN_CM(2.8V)
  3. Unipolar:
    (1)AVDD:
    Use Another DC Source like DC12V.
    DC12V(11.5V~12.5V) → LDO (+5V output)
    (2)AVSS = GND.
    (3)VREF: REF6025(2.5V)
    I get the results as bellow    : (PASS)

    Which of these methods do you suggest to use? (Or other suggestion?) Why?

     

    Best Regards

    Jax

  • 0
    TI__Mastermind 35081 points

    Hi Jax,

    It seems like you do need a 5V unipolar supply in this case, so either #1 or #3 is best. As long as you are using a clean, low noise, low ripple supply voltage, it is more up to you to determine how to generate this voltage. So that would depend on the power requirements, the PCB space constraints, whether you want to just use USB power, what voltages are available in the system, etc. In other words, I don't have much help to offer you in making this decision, it depends on your system requirements. But again, I believe either solution you came up with should work (#1 or #3).

    -Bryan