adc12041 National Semiconductor Corporation, adc12041 Datasheet - Page 23

• Manufacturer Part Number: adc12041
• Description: 12-bit Plus Sign 216 Khz Sampling Analog-to-digital Converter
• Manufacturer: National Semiconductor Corporation

Features and Operating Modes
degrade the conversion result. In the SYNC-IN mode, only
the rising edge of the SYNC signal will begin a conversion
cycle. The RDY signal will go low when the conversion cycle
is done. The acquisition time is controlled by the SYNC sig-
nal. The acquisition period begins after the falling edge of the
RDY signal. The input is sampled until the rising edge of the
SYNC pulse, at which time the signal will be held and con-
version begins. The RDY signal will go low when the conver-
sion is done and a new operational command may be written
into the Configuration register at this time, if needed. With
the START command in the Configuration register, a read
from the ADC12041 will place the entire conversion result
stored in the Data register on the data bus and the rising
edge of the read pulse will force the RDY signal high.
STANDBY COMMAND
8-bit mode: A write to the ADC12041 should clear the BW bit
and issue the Standby command.
13-bit mode: A write to the ADC12041 should set the BW bit
and issue the Standby command.
RESET
The RESET command places the ADC12041 into a ready
state and forces the RDY signal low. The RESET command
can be used to interrupt the ADC12041 while it is performing
a conversion, full-calibration or auto-zero cycle. It can also
be used to get the ADC12041 out of the standby mode.
Analog Application Information
REFERENCE VOLTAGE
The ADC12041 has two reference inputs, V
They define the zero to full-scale range of the analog input
signals over which 4095 positive and 4096 negative codes
exist. The reference inputs can be connected to span the en-
tire supply voltage range (V
they can be connected to different voltages when other input
spans are required. The reference inputs of the ADC12041
have transient capacitive switching currents. The voltage
sources driving V
impedence and noise and must be adequately bypassed.
The circuit in Figure 20 is an example of a very stable refer-
ence source.
The ADC12041 can be used in either ratiometric or absolute
reference applications. In ratiometric systems, the analog in-
(Continued)
REF
+ and V
REF
REF
− = AGND, V
− must have very low output
REF
REF
+ and V
+ = V
A
REF
+) or
−.
23
put voltage is proportional to the voltage used for the ADC’s
reference voltage. This technique relaxes the system refer-
ence requirements because the analog input voltage moves
with the ADC’s reference. The system power supply can be
used as the reference voltage by connecting the V
to V
where the analog input voltage varies between very specific
voltage limits, a time and temperature stable voltage source
can be connected to the reference inputs. Typically, the ref-
erence voltage’s magnitude will require an initial adjustment
to null reference voltage induced full-scale errors.
The reference voltage inputs are not fully differential. The
ADC12041 will not generate correct conversions if
(V
able relationship between V
OUTPUT DIGITAL CODE VERSUS ANALOG INPUT
VOLTAGE
The ADC12041’s fully differential 12-bit + sign ADC gener-
ates a two’s complement output that is found by using the
equation shown below:
Round off the result to the nearest integer value between
-4096 and 4095.
REF
A
+ and the V
+) – (V
FIGURE 19. V
REF
−) is below 1V. Figure 19 shows the allow-
REF
− pin to AGND. For absolute accuracy,
REF
REF
Operating Range
+ and V
REF
−.
DS012441-43
www.national.com
REF
+ pin