ADC12L030CIWM National Semiconductor, ADC12L030CIWM Datasheet - Page 29

• Manufacturer Part Number: ADC12L030CIWM
• Description: 3.3V Self-Calibrating 12-Bit Plus Sign Serial I/O A/D Converters with MUX and Sample/Hold
• Manufacturer: National Semiconductor

Application Hints
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-
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 ref-
erence inputs. Typically, the reference voltage’s magnitude
will require an initial adjustment to null reference voltage in-
duced full-scale errors.
Below are recommended references along with some key
specifications.
The reference voltage inputs are not fully differential. The
ADC12L030/2/4/8 will not generate correct conversions or
comparisons if V
sions result when V
at all times, between ground and V
mode range, (V
(0.6 x V
LM4041CIM3-Adj
LM4040AIM3-2.5
REF
REF
Part Number
−
−
defines the analog input span (the difference between
is connected to ground. This technique relaxes the
A
+
). Therefore, with V
REF
REF
+
REF
+
+ V
is taken below V
+
REF
and V
REF
Tolerance
Voltage
−
Output
±
±
)/2, is restricted to (0.1 x V
+
A
0.5%
0.1%
+
(Continued)
REF
pin is connected to V
= 3.3V the center of the ref-
−
REF
differ by 1V and remain,
A
+
REF
+
. The V
or V
−
Temperature
. Correct conver-
±
±
FIGURE 14. Fully Differential Biasing
Coefficient
REF
100ppm/˚C
100ppm/˚C
REF
(max)
−
must have
REF
common
A
+
+
A
+
and
and
) to
29
erence ladder should not go below 0.33V or above 1.98V.
Figure 15 is a graphic representation of the voltage restric-
tions on V
REF
FIGURE 15. V
+
and V
REF
−
REF
.
Operating Range
DS011830-50
www.national.com
DS011830-43