adc12132 National Semiconductor Corporation, adc12132 Datasheet - Page 34

• Manufacturer Part Number: adc12132
• Description: 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 circuit in Figure
16 is an example of a very stable reference appropriate for
use with the device.
*Tantalum
The ADC12130/2/8 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-
tions. For absolute accuracy, where the analog input voltage
REF
REF
−
−
defines the analog input span (the difference between
is connected to ground. This technique relaxes the
FIGURE 16. Low Drift Extremely
Stable Reference Circuit
REF
+
pin is connected to V
REF
+
or V
(Continued)
FIGURE 15. Fully Differential Biasing
REF
−
must have
REF
A
+
01207943
+
and
and
34
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.
The reference voltage inputs are not fully differential. The
ADC12130/2/8 will not generate correct conversions or com-
parisons if V
result when V
times, between ground and V
range, (V
V
ladder should not go below 0.5V or above 3.0V. Figure 17 is
a graphic representation of the voltage restrictions on V
and V
LM4041CI-Adj
LM4040AI-4.1
LM4050AI-4.1
Circuit of Figure 16
A
+
). Therefore, with V
REF
Part Number
REF
−
.
REF
+
REF
+ V
+
+
is taken below V
REF
and V
−
)/2 is restricted to (0.1 x V
A
+
REF
= 5V the center of the reference
−
Tolerance
Adjustable
differ by 1V and remain, at all
A
Voltage
Output
+
±
±
±
. The V
0.5%
0.1%
0.1%
REF
−
. Correct conversions
01207942
REF
Temperature
common mode
±
±
Coefficient
±
±
100ppm/˚C
100ppm/˚C
50ppm/˚C
2ppm/˚C
A
+
) to (0.6 x
REF
+