sparkfun Qwiic 12-Bit ADC Hook-Up Manual page 10

Limitation of ADS1015
Since the ADS1015 only uses an internal reference voltage, the FSR is to be defined by the design of the 12-bit
ADC:
12
FSR = LSB x 2
where, the LSB = 0.125, 0.25, 0.5, 1, 2, or 3 mV.
Due to the configuration options, it is difficult to make full use of the full-scale range of the ADS1015 with common
(useful) voltages. See the examples below for a more detailed explanation:
If the FSR = 2.048V and V
Resolution of the digital data: 1mV (defined by FSR)
Input voltage range: 0-3.3V (defined by V
Data Range: 0000h-7FF0h (HEX) or 0-2.048V
The range of the input voltage that can be read by the ADC is limited by FSR. Any voltage higher than the
FSR (but less than V
out. In this case, you are maximizing the resolution (use of the data output), but not the full, allowable range
of analog input (0-3.3V).
If the FSR = 4.096V and V
Resolution of the digital data: 2mV (defined by FSR)
Input voltage range: 0-3.3V (defined by V
Data Range: 0000h-0672h (HEX) or 0-3.3V
The data range is limited by V
specifications of the ADS1015 ~V
being maximized to the electrical specification (0-3.3V). However, this means you are effectively only using
80% of the full resolution of the ADC (i.e. a 10.8-bit ADC at 3.3V).
Data Rate & Conversion Time
The ADS1015 offers 7 selectable output data rates of 128 SPS, 250 SPS, 490 SPS, 920 SPS, 1600 SPS, 2400
SPS, or 3300 SPS. Conversions for the ADS1015 settle within a single cycle; thus, the conversion time is equal to
1/DR.
Programmable Digital Comparator
Explanation of how data output and sign bit work from datasheet.
= 3.3V:
DD
DD
) reads the same maximum value in the digital output because the FSR is maxed
DD
= 3.3V:
DD
DD
, any higher input voltage will continue to have data up to the electrical
DD
+ 0.3V, where the IC gets damaged. In this case, the input voltage is
DD
)
)