adc12l032 National Semiconductor Corporation, adc12l032 Datasheet - Page 28

• Manufacturer Part Number: adc12l032
• Description: 3.3v Self-calibrating 12-bit Plus Sign Serial I/o A/d Converters With Mux And Sample/hold
• Manufacturer: National Semiconductor Corporation

www.national.com
Application Information
3.0 REFERENCE VOLTAGE
The difference in the voltages applied to the V
V
the voltage applied between two multiplexer inputs or the
voltage applied to one of the multiplexer inputs and analog
ground), over which 4095 positive and 4096 negative codes
exist. The voltage sources driving V
very low output impedance and noise.
The ADC12L030/2/4/8 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. When this voltage is the sys-
tem power supply, the V
V
system reference stability requirements because the analog
input voltage and the ADC reference voltage move together.
This maintains the same output code for given input condi-
REF
REF
−
−
defines the analog input span (the difference between
is connected to ground. This technique relaxes the
FIGURE 13. Pseudo-Differential Biasing with the Signal Source AC Coupled Directly into the ADC
REF
+
pin is connected to V
REF
+
or V
(Continued)
FIGURE 14. Fully Differential Biasing
REF
−
must have
REF
A
+
+
and
and
28
tions. For absolute accuracy, where the analog input voltage
varies between very specific voltage limits, a time and tem-
perature stable voltage source can be connected to the
reference inputs. Typically, the reference voltage’s magni-
tude will require an initial adjustment to null reference volt-
age induced full-scale errors.
Below are recommended references along with some key
specifications.
LM4041CIM3-Adj
LM4040AIM3-2.5
LM4050AIM3-2.5
Part Number
Tolerance
Voltage
Output
±
±
±
01183050
0.5%
0.1%
0.1%
01183047
Temperature
±
±
Coefficient
±
100ppm/˚C
100ppm/˚C
50ppm/˚C
(max)