ZHCSII0A July 2018 – November 2018 ADS1219
PRODUCTION DATA.
The ADS1219 integrates two rail-to-rail input buffers to ensure that the effect on the input loading resulting from the capacitor charging and discharging of the ΔΣ ADC is minimal. The buffers therefore help to increase the input impedance of the device. See the Electrical Characteristics table for the typical values of absolute input currents (current flowing into or out of each input) and differential input currents (difference in absolute current between the positive and negative input).
The usable absolute input voltage range of the buffers is (AGND – 0.1 V ≤ VAINP, VAINN ≤ AVDD + 0.1 V). VIN denotes the differential input voltage VIN = VAINP – VAINN between the buffer inputs.
A programmable gain stage follows the buffers. The GAIN bit in the configuration register is used to configure the gain to either 1 or 4.
Equation 4 shows that the differential full-scale input voltage range (FSR) of the device is defined by the gain setting and the reference voltage used:
Table 3 shows the corresponding full-scale ranges and least significant bit (LSB) sizes when using the internal 2.048-V reference.
| GAIN SETTING | FSR | LSB SIZE |
|---|---|---|
| 1 | ±2.048 V | 244.14 nV |
| 4 | ±0.512 V | 61.04 nV |
In order to measure single-ended signals that are referenced to AGND (AINP = VIN, AINN = AGND), connect one of the analog inputs to AGND externally or use the internal AGND connection of the multiplexer (MUX[2:0] settings 011 through 110). The device only uses the code range that represents positive differential voltages when measuring single-ended signals. See the Data Format section for more details.
For signal sources with high output impedance, external buffering may still be necessary. Active buffers can introduce noise as well as offset and gain errors. Consider all of these factors in high-accuracy applications.