參數(shù)資料
型號: ADC12032
廠商: National Semiconductor Corporation
元件分類: 串行ADC
英文描述: Self-Calibrating 12-Bit Plus Sign Serial I/O A/D Converters with MUX and Sample/Hold
中文描述: 自校準12位帶符號串行I /辦公自動化/ D轉換器MUX和采樣/保持
文件頁數(shù): 34/41頁
文件大?。?/td> 1036K
代理商: ADC12032
Application Hints
(Continued)
TheADC 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
REF+
pin is connected to V
A+
and
V
REF
is connected to ground. This technique relaxes the
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.
Output
Voltage
Tolerance
±
0.5%
±
0.1%
Adjustable
Temperature
Coefficient
Part Number
LM4041CI-Adj
LM4040AI-4.1
Circuit of
Figure 16
The reference voltage inputs are not fully differential. The
ADC12030/2/4/8 will not generate correct conversions or
comparisons if V
REF+
is taken below V
REF
. Correct conver-
sions result when V
REF+
and V
REF
differ by 1V and remain,
at all times, between ground and V
A+
. The V
common
mode range, (V
REF+
+ V
REF
)/2 is restricted to (0.1 x V
A+
) to
(0.6 x V
A+
). Therefore, with V
A+
= 5V the center of the refer-
ence ladder should not go below 0.5V or above 3.0V. Figure
17 is a graphic representation of the voltage restrictions on
V
REF+
and V
REF
.
±
100ppm/C
±
100ppm/C
±
2ppm/C
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:
for (12-bit) resolution the Output Code =
for (8-bit) resolution the Output Code =
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:
Digital
Output
Code
V
REF+
V
REF
V
IN+
V
IN
+2.5V
+4.096V
+4.096V
+4.096V
+1V
0V
0V
0V
+1.5V
+3V
+2.499V
0V
0V
0V
0,1111,1111,1111
0,1011,1011,1000
1,1111,1111,1111
1,0000,0000,0000
+2.500V
+4.096V
5.0 INPUT CURRENT
At the start of the acquisition window (t
) a charging current
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 andA/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
DS011354-42
*
Tantalum
FIGURE 16. Low Drift Extremely
Stable Reference Circuit
DS011354-45
FIGURE 17. V
REF
Operating Range
www.national.com
34
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