ZHCSMK4A september 2022 – july 2023 ADS131B26-Q1
PRODUCTION DATA
ADC2y features an integrated programmable gain amplifier (PGA) that provides gains of 1, 2, and 4. Select the gain setting using the SEQ2y_STEPn_GAIN[1:0] bits.
Varying the PGA gain scales the differential full-scale input voltage range (FSR) of ADC2y. Equation 9 describes the relationship between FSR and gain. Equation 9 uses the internal reference voltage, 1.25 V, as the scaling factor without accounting for gain error caused by tolerance in the reference voltage.
Table 9-8 shows the corresponding full-scale ranges for each gain setting.
GAIN SETTING | FSR |
---|---|
1 | ±1.25 V |
2 | ±625 mV |
4 | ±312.5 mV |
When performing single-ended measurements (that is, AGNDy is selected as the negative multiplexer channel for ADC2y), gain settings of 1 and 2 only allow for unipolar measurements, whereas gain setting of 4 allows for both unipolar and bipolar input voltage measurements. See the absolute input voltage range specification of ADC2y in the Recommended Operating Conditions table for details and the ADC2y Measurement Configurations section for example input configurations. Unipolar measurements only use the positive code range from approximately 0000h to 7FFFh, which maps to an input voltage range from approximately 0 V to +FS.
The input impedance of the ADC2y channel depends on two factors: the main clock frequency (fMCLK) and the selected OSR setting. The Electrical Characteristics table lists typical input impedance values for fMCLK = 8.192 MHz at the various OSR settings. Increasing the OSR by twice the value effectively doubles the input impedance. The input impedance scales indirectly proportional with the MCLK frequency.