The ADC121S051CISDX/NOPB is a 12-bit, single-channel successive-approximation ADC from Texas Instruments, sampling at 500 kSPS and housed in a 6-pin WSON package.
What the 12-bit 500 kSPS rating means for your BOM
12-bit resolution gives 4096 codes across the input range — for a 5 V reference, each LSB represents about 1.22 mV. That is enough granularity for most sensor-conditioning and control loops, but the effective resolution at the signal-to-noise ratio may be lower than the raw bit count. 500 kSPS throughput means the ADC completes a conversion every 2 µs. The serial interface must clock out the 12-bit result within that window, so the SPI bus speed needs to be at least 6 MHz to avoid back-to-back sampling gaps.