ADC12030CIWM National Semiconductor, ADC12030CIWM Datasheet - Page 34

• Manufacturer Part Number: ADC12030CIWM
• Description: Self-Calibrating 12-Bit Plus Sign Serial I/O A/D Converters with MUX and Sample/Hold
• Manufacturer: National Semiconductor

www.national.com
Application Hints
*
The ADC 12030/2/4/8 can be used in either ratiometric or ab-
solute 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
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 x 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
Tantalum
LM4041CI-Adj
LM4040AI-4.1
Circuit of Figure 16
REF
REF
−
+
Part Number
and V
is connected to ground. This technique relaxes the
A
+
). Therefore, with V
FIGURE 16. Low Drift Extremely
REF
REF
−
Stable Reference Circuit
REF
.
+
REF
+
+ V
is taken below V
+
REF
and V
REF
−
+
)/2 is restricted to (0.1 x V
A
Tolerance
Adjustable
+
(Continued)
Voltage
pin is connected to V
REF
Output
±
±
= 5V the center of the refer-
0.5%
0.1%
−
differ by 1V and remain,
A
+
REF
. The V
−
. Correct conver-
Temperature
Coefficient
±
±
REF
100ppm/˚C
100ppm/˚C
±
2ppm/˚C
common
DS011354-42
A
+
A
+
and
) to
34
4.0 ANALOG INPUT VOLTAGE RANGE
The ADC12030/2/4/8’s fully differential ADC generate a
two’s complement output that is found by using the equa-
tions shown below:
Round off to the nearest integer value between −4096 to
4095 for 12-bit resolution and between −256 to 255 for 8-bit
resolution if the result of the above equation is not a whole
number.
Examples are shown in the table below:
5.0 INPUT CURRENT
At the start of the acquisition window (t
flows into or out of the analog input pins (A/DIN1 and
A/DIN2) depending on the input voltage polarity. The analog
input pins are CH0–CH7 and COM when A/DIN1 is tied to
MUXOUT1 and A/DIN2 is tied to MUXOUT2. The peak value
of this input current will depend on the actual input voltage
applied, the source impedance and the internal multiplexer
switch on resistance. With MUXOUT1 tied to A/DIN1 and
+4.096V
+4.096V
+4.096V
V
+2.5V
for (12-bit) resolution the Output Code =
for (8-bit) resolution the Output Code =
REF
+
V
FIGURE 17. V
+1V
REF
0V
0V
0V
−
+2.499V +2.500V 1,1111,1111,1111
+1.5V
V
+3V
0V
IN
+
REF
+4.096V 1,0000,0000,0000
Operating Range
V
0V
0V
IN
−
A
0,1111,1111,1111
0,1011,1011,1000
) a charging current
Output
Digital
Code
DS011354-45