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ADS1258-EP: Design Questions for multi sensor measurements

Tobias Heib
Prodigy 10 points
Part Number: ADS1258-EP
Other Parts Discussed in Thread: ADS1258, REF2025, BUF634

Hello,

1. We want to measure 16 sensors single ended with the ADS1258. The sensors are configured as a quarter bridge with the circuit taken from the TI example below. R10 being the sensor element in the bridge. With the given VREFP of +2.5V and supply voltage of +5V, the bridge circuit delivers a voltage range from above +0V to below +5V. VREFN is GND. We hope this is reasonable?

The Reference we use is REF2025, with a Buffer to supply the 16 bridges BUF634.

Single-Supply Strain Gauge Bridge Amplifier Circuit (Rev. A) (ti.com)

2. We are not sure what to do with AINCOM? Does this has to be +2.5V? And thus VREFP +5V?

Thanks a lot

  • 0
    TI__Mastermind 43901 points

    Hi Tobias Heib,

    Here are the answers to your questions:

    Tobias Heib said:
    1. We want to measure 16 sensors single ended with the ADS1258. The sensors are configured as a quarter bridge with the circuit taken from the TI example below. R10 being the sensor element in the bridge. With the given VREFP of +2.5V and supply voltage of +5V, the bridge circuit delivers a voltage range from above +0V to below +5V. VREFN is GND. We hope this is reasonable?

    Yes, this seems reasonable. Though I don't see a connection from VREFN to ground in your schematic

    Tobias Heib said:
    2. We are not sure what to do with AINCOM? Does this has to be +2.5V? And thus VREFP +5V?

    If you want to measure 16 single-ended channels then you would need to use Auto-Scan mode. In this mode, each single-ended input is measured against AINCOM. If you want to measure a signal range from 0V to 5V, I would tie AINCOM to 2.5V. This is called a pseudo differential measurement, and allows you to measure differentially from -2.5V (when VIN = 0V) to +2.5V (when VIN = 5V), thereby taking advantage of the entire ADC full scale range.

    I am not sure why VREFP = 5V though

    I would also caution against using a crystal for the ADC clock instead of a discrete clock oscillator. Many customers have had issues getting the crystal to oscillate with the ADS1258 (you can search e2e for more information). I would recommend using a discrete clock oscillator for best, most consistent performance

    -Bryan