• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 46 subscribers
  • Views 986 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS1259-Q1: Driving with INA240, plus another question

Brian Antheunisse
Expert 5305 points
Part Number: ADS1259-Q1
Other Parts Discussed in Thread: INA240, ADS1259, OPA376-Q1, ADS1120-Q1

Hi teams,

I have a customer who is thinking about designing a system using the ADS1259-Q1 to sense current. The current shunt amplifier will be the INA240. You guys don't see any issues with that part driving the ADC directly, do you? Likely they will be sampling at about 1ksps. They are doing high side sensing, and the output of the amp could be 0V-1.5V across their current sensing range. 

Also, it looks like the ADS1259-Q1 is dual supplied for both the analog and digital.  Since the processor will be on 3v3, but the part's analog supply really needs to be at 5V, can the part handle both 3v3 on the digital and 5v on the analog?  I just want to make sure that there's nothing funny with latchup/level shifting that may impact the operation of the part.

Thanks,

Brian

  • 0
    TI__Mastermind 44720 points
    Hi Brian,

    I was looking into your question, but at the moment I don't have enough information on the INA240 to know for sure how it will perform when driving the ADS1259 directly...

    I'd be a bit concerned with the low-bandwidth (< 1 MHz) and the small capacitive load drive (1 nF) specifications that would hint at potential issues. Usually we'd also like to know the output-impedance of the device and try to simulate the performance; however, I wan't able to track down this information or a SPICE model of the device.

    To be safe, you might suggest buffering the INA240 with the OPA376-Q1. The customer could always compare results without and without the buffer when doing their initial evaluation of the circuit and decide whether it would be required in their final design, or if they are able to achieve sufficient performance without it.

    Regarding the dual-supply configuration for the ADS1259...
    There is no problem using a 5V supply for AVDD and a 3.3V supply for DVDD, so long as these supplies are referenced to the same ground potential (either use a single ground plane for both analog and digital, or as a minimum, make sure the analog (AVSS) and digital grounds (DGND) are shorted together directly at the ADC).

    Best Regards,
    Chris
  • 0 in reply to Christopher Hall
    TI__Expert 5305 points
    If they are sampling at only ~1ksps, do you think the BW and drive strength have a better chance to do the job?

    I will absolutely pass along the advice.

    Thanks,
    Brian
  • 0 in reply to Brian Antheunisse
    TI__Mastermind 44720 points

    Hi Brian,

    In this case, since the ADS1259 is a delta-sigma ADC, changing the data rate will have no impact on the ADC's sampling rate. Delta-sigma ADCs oversample the input and decimate data during filtering; therefore, the sampling rate usually remains fixed even when scaling the data rate.

    I looked at the INA240 a bit more closely and see that it's noise performance is quite poor when compared to the ADS1259's noise performance...With 40 nVrms/sqrt(Hz), 1000 Hz bandwidth and a gain of 20 V/V, you'd expect to see 40 nVrms/sqrt(Hz) *sqrt(1000 Hz)* 20 V/V *6 c.f. = 152 uVpp of noise. For comparison, the ADS1259's noise performance at the 1200 SPS data rate is 14-17 uVpp (18.2-18.4 noise-free bits). In this case due to the noise of the INA, there is no benefit from using a 24-bit ADC, the same resolution can be achieved with a 16-bit ADC!

    They might want consider using an ADS1120-Q1 with an integrated PGA to buffer the input signal.

    Best Regards,
    Chris

  • 0 in reply to Christopher Hall
    TI__Expert 5305 points
    Right, totally makes sense regarding the BW vs sampling rate question.

    And thanks a ton for the analysis. You may have just helped my customer save a lot of money. I've passed the info along.

    Regards,
    Brian
  • 0 in reply to Brian Antheunisse
    TI__Mastermind 44720 points
    Glad to help. Let me know if you have any additional questions!

    BR,
    Chris