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Original question:

ADS1260: ADS1260 : Need to measure uA current ADC solution_circuit

ADS1260: Question of parameters and Referece voltage.

Jax Yang
Prodigy 50 points
Part Number: ADS1260
Other Parts Discussed in Thread: REF6045, REF6025

Hi bro,

For the uA solution of ADS1260:

If I choose bigger value R-shunt = 500mΩ for much buffer of avoiding noise,

 (1) Vshunt_Max = Isense_Max x Rshunt = 50mA x 500mΩ = 25mV

 (2) Dynamic Range = Isense_Max / Iresolution = 50mA / 1uA = 50000

 -> (3)Vresolution = Vsense_Max / Dynamic Range  = 0.5uV

 

I can choose PGA Gain =128 for best performance.

Q1: If the current flow direction is only one-way.

For more VIN_DIFF Range and lower Dropout voltage,
is 4.5 V(REF6045) better for Reference voltage instead of 2.5V(REF6025)?

(2) In ADS1260 Datasheet, I get confused in the Table 4:

What is the correct value of Full-scale Diff. input range when Gain =64, 128?
The value in Table 4 is mismatch to the formula rule “gain = 32,64 , use gain = 32 in the calculation”.

Thanks.

-Jax

  • +1
    TI__Mastermind 38971 points

    Hi Jax,

    Here are the answers to your questions:

    1. The ADS1260 can accept a 4.5 V reference voltage, so the REF6045 will work just as well as the REF6025. Therefore, if the REF6045 offers benefits to your system (larger VDIFF, lower dropout voltage), then I don't see a reason why you should not use it
    2. The PGA absolute input range limitations result from the PGA architecture. The analog PGA only has a gain of 32, and the higher gains are achieved digitally, which is why the analog input voltage restrictions are only valid for gains up to 32. In other words, there is gain being applied such that the maximum differential input voltage is reduced, but this does not affect the analog input restrictions for gains of 64 and 128.

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 50 points

    Hi Bryan,

    Thanks!

     

    By the way, I use the tool(ADS1261-60 Design Calculator) and discover something different with datasheet in ADS1260.
     

     

    Are VIN_DIFF Range in tool and Full-Scale Voltage Range in datasheet the same parameter?
    I found them are the same unless I use Gain = 64 or 128. The value of VIN_DIFF Range in tool remains 0.0781, but the the value of Full-Scale Voltage Range in datasheet changed.

     

    Thanks.

    -Jax

  • 0 in reply to Jax Yang
    TI__Mastermind 38971 points

    Hi Jax,

    Thanks for pointing this out, I do believe this is an error. As noted in my last post, the VCM range should not be affected by gains > 32, but the VDIFF range should get smaller for gains > 32. I will work to update this in the tool and push a new version to TI.com. This may take a week or so however.

    Please let me know if you need anything else.

    -Bryan