AD9243 Analog Devices, AD9243 Datasheet - Page 16

• Manufacturer Part Number: AD9243
• Description: Complete 14-Bit, 3 MSPS Monolithic A/D Converter
• Manufacturer: Analog Devices

Specifications of AD9243

• Resolution (bits): 14bit
• # Chan: 1
• Sample Rate: 3MSPS
• Interface: Par
• Analog Input Type: Diff-Uni,SE-Uni
• Ain Range: (2Vref) p-p,2 V p-p,5V p-p,Uni (Vref) x 2,Uni 2.0V,Uni 5.0V
• Adc Architecture: Pipelined
• Pkg Type: QFP

AD9243
Shorting the VREF pin directly to the SENSE pin places the
internal reference amplifier in unity-gain mode and the resultant
VREF output is 1 V. Therefore, the valid input range is 0 V to
2 V. However, shorting the SENSE pin directly to the REFCOM
pin configures the internal reference amplifier for a gain of 2.5
and the resultant VREF output is 2.5 V. Thus, the valid input
range becomes 0 V to 5 V. The VREF pin should be bypassed
to the REFCOM pin with a 10 F tantalum capacitor in parallel
with a low-inductance 0.1 F ceramic capacitor.
Single-Ended or Differential Input, V
Figure 37 shows the single-ended configuration that gives the
best SINAD performance. To optimize dynamic specifications,
center the common-mode voltage of the analog input at
approximately by 2.5 V by connecting VINB to VREF, a low-
impedance 2.5 V source. As described above, shorting the
SENSE pin directly to the REFCOM pin results in a 2.5 V
reference voltage and a 5 V p-p input span. The valid range
for input signals is 0 V to 5 V. The VREF pin should be by-
passed to the REFCOM pin with a 10 F tantalum capacitor in
parallel with a low inductance 0.1 F ceramic capacitor.
This reference configuration could also be used for a differential
input in which VINA and VINB are driven via a transformer as
shown in Figure 29. In this case, the common-mode voltage,
V
tap to CML of the AD9243. VREF can be configured for 1 V
or 2.5 V by connecting SENSE to either VREF or REFCOM
respectively. Note that the valid input range for each of the
differential inputs is one half of the single-ended input and thus
becomes V
CM
Figure 37. Internal Reference—5 V p-p Input Span,
V
CM
, is set at midsupply by connecting the transformers center
2xVREF
Figure 36. Internal Reference (2 V p-p Input Span,
V
CM
= 2.5 V
0V
= 1 V, or 5 V p-p Input Span, V
CM
5V
0V
– VREF/2 to V
10 F
SHORT FOR 0V TO 2V
SHORT FOR 0V TO 5V
10 F
0.1 F
INPUT SPAN
INPUT SPAN
2.5V
CM
+ VREF/2.
0.1 F
VINA
VINB
VREF
SENSE
REFCOM
CM
= 2.5 V
CM
AD9243
VINA
VINB
VREF
SENSE
REFCOM
= 2.5 V)
AD9243
–16–
Resistor Programmable Reference
Figure 38 shows an example of how to generate a reference
voltage other than 1 V or 2.5 V with the addition of two exter-
nal resistors and a bypass capacitor. Use the equation,
to determine appropriate values for R1 and R2. These resistors
should be in the 2 k to 100 k range. For the example shown,
R1 equals 2.5 k and R2 equals 5 k . From the equation
above, the resultant reference voltage on the VREF pin is
1.5 V. This sets the input span to be 3 V p-p. To assure stabil-
ity, place a 0.1 F ceramic capacitor in parallel with R1.
The common-mode voltage can be set to VREF by connecting
VINB to VREF to provide an input span of 0 to 2
Alternatively, the common-mode voltage can be set to 2.5 V
by connecting VINB to a low impedance 2.5 V source. For
the example shown, the valid input single range for VINA is
1 V to 4 V since VINB is set to an external, low impedance 2.5
V source. The VREF pin should be bypassed to the REFCOM
pin with a 10 F tantalum capacitor in parallel with a low induc-
tance 0.1 F ceramic capacitor.
USING AN EXTERNAL REFERENCE
Using an external reference may enhance the dc performance of
the AD9243 by improving drift and accuracy. Figures 39
through 41 show examples of how to use an external reference
with the A/D. Table III is a list of suitable voltage references
from Analog Devices. To use an external reference, the user
must disable the internal reference amplifier and drive the VREF
pin. Connecting the SENSE pin to AVDD disables the inter-
nal reference amplifier.
Internal
AD589
AD1580
REF191
Internal
REF192
REF43
AD780
Figure 38. Resistor Programmable Reference (3 V p-p
Input Span, V
1V
4V
10 F
Output
Voltage
1.00
1.235
1.225
2.048
2.50
2.50
2.50
2.50
2.5V
Table III. Suitable Voltage References
CM
VREF = 1 V
0.1 F
= 2.5 V)
26
26
Drift
(ppm/ C)
10–100
50–100
5–25
5–25
10–25
3–7
R1
2.5k
R2
5k
(1 + R1/R2),
C1
0.1 F
1.5V
Initial
Accuracy
% (max)
1.4
1.2–2.8
0.08–0.8
0.1–0.5
1.4
0.08–0.4
0.06–0.1
0.04–0.2
VINB
SENSE
REFCOM
VINA
VREF
AD9243
Operating
Current
N/A
50
50
45
N/A
45
600
1000
( A)
VREF.
REV. A