TIDUF13 November 2022 ADS117L11 , ADS127L11
IEPE sensors need an excitation current in the range of 2 mA to 20 mA to operate, based on the connecting cable length, and the load capacitance. In most IEPE applications, a static 2–4 mA is sufficient to operate the sensor. The accuracy of the current source is not critical but the compliance range, current noise, and load regulation are important for the interface performance.
For this design, a static 3.5-mA current source is developed using a low-voltage shunt reference and an op amp. Low voltage reference provides low headroom and higher compliance range. A cost-effective design is achieved using a quad op-amp OPA4187 package.
For more details about the current source design, see the High-side current sources for industrial applications Analog Design Journal article.
Since this application runs from a 5-V source, a booster stage is required to generate the high voltage for the current source. A TLV61046A compact boosting stage is used followed by the TPS7A49 LDO to generate a clean 23.8 V for the current sources. The current source has about 1.5-V headroom, leaving a compliance range up to 22 V.