ADC12034 National Semiconductor Corporation, ADC12034 Datasheet - Page 36

• Manufacturer Part Number: ADC12034
• 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
3.0 REFERENCE VOLTAGE
The difference in the voltages applied to the V
−
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
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 ADC12030/2/4/8 can be used in either ratiometric or ab-
solute reference applications. In ratiometric systems, the ana-
log input voltage is proportional to the voltage used for the
ADC's reference voltage. When this voltage is the system
power supply, the V
connected to ground. This technique relaxes the system ref-
erence stability requirements because the analog input volt-
age and the ADC reference voltage move together. This
maintains the same output code for given input conditions.
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 in-
puts. Typically, the reference voltage's magnitude will require
defines the analog input span (the difference between the
FIGURE 16. Low Drift Extremely
Stable Reference Circuit
REF
+
pin is connected to V
REF
+
or V
REF
−
must have very low
FIGURE 15. Fully Differential Biasing
A
REF
+
and V
+
and V
REF
1135442
REF
−
is
36
an initial adjustment to null reference voltage induced full-
scale errors.
Below are recommended references along with some key
specifications.
The reference voltage inputs are not fully differential. The
ADC12030/2/4/8 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 × V
ence ladder should not go below 0.5V or above 3.0V. Figure
17 is a graphic representation of the voltage restrictions on
V
LM4041CI-Adj
LM4040AI-4.1
LM4120AI-4.1
LM4121AI-4.1
LM4050AI-4.1
LM4030AI-4.1
LM4140AC-4.1
Circuit of Figure 16
REF
+
and V
Part Number
A
+
). Therefore, with V
REF
−
REF
.
REF
+
REF
+
+ V
is taken below V
+
REF
and V
−
)/2 is restricted to (0.1 × V
A
Tolerance
Adjustable
+
REF
Voltage
±0.05%
Output
±0.5%
±0.1%
±0.2%
±0.2%
±0.1%
±0.1%
= 5V the center of the refer-
−
differ by 1V and remain,
A
+
REF
. The V
1135450
−
. Correct conver-
Temperature
Coefficient
±100ppm/°C
±100ppm/°C
±3.0ppm/°C
REF
±50ppm/°C
±50ppm/°C
±50ppm/°C
±10ppm/°C
±2ppm/°C
common
A
+
) to