Datasheet

ADC12048
SNAS105B –APRIL 2000–REVISED MARCH 2013 www.ti.com
Analog Application Information
REFERENCE VOLTAGE
The ADC12048 has two reference inputs, V
REF
+ and V
REF
−. They define the zero to full-scale range of the
analog input signals over which 4095 positive and 4096 negative codes exist. The reference inputs can be
connected to span the entire supply voltage range (V
REF
− = AGND, V
REF
+ = V
A
+) or they can be connected to
different voltages when other input spans are required. The reference inputs of the ADC12048 have transient
capacitive switching currents. The voltage sources driving V
REF
+ and V
REF
− must have very low output
impedance and noise and must be adequately bypassed. The circuit in Figure 48 is an example of a very stable
reference source.
The ADC12048 can be used in either ratiometric or absolute reference applications. In ratiometric systems, the
analog input voltage is proportional to the voltage used for the ADC's reference voltage. This technique relaxes
the system reference requirements because the analog input voltage moves with the ADC's reference. The
system power supply can be used as the reference voltage by connecting the V
REF
+ pin to V
A
+ and the V
REF
−
pin to AGND. For absolute accuracy, where the analog input voltage varies between very specific voltage limits,
a time and temperature stable voltage source can be connected to the reference inputs. Typically, the reference
voltage's magnitude will require an initial adjustment to null reference voltage induced full-scale errors.
The reference voltage inputs are not fully differential. The ADC12048 will not generate correct conversions if
(V
REF
+) – (V
REF
−) is below 1V. Figure 47 shows the allowable relationship between V
REF
+ and V
REF
−.
Figure 47. V
REF
Operating Range
*Tantalum
**Ceramic
Figure 48. Low Drift Extremely Stable Reference Circuit
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