AD9221ARZ Analog Devices Inc, AD9221ARZ Datasheet - Page 19

• Manufacturer Part Number: AD9221ARZ
• Description: 12-Bit 1.25 MSPS Monolithic ADC
• Manufacturer: Analog Devices Inc

Specifications of AD9221ARZ

• Number Of Bits: 12
• Sampling Rate (per Second): 1.5M
• Data Interface: Parallel
• Number Of Converters: 7
• Power Dissipation (max): 70mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-SOIC (0.300", 7.50mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: AD9221-EB - BOARD EVAL FOR AD9221
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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 µF tantalum capacitor in parallel with a
low inductance 0.1 µF ceramic capacitor.
Single-Ended or Differential Input, V
Figure 22 shows the single-ended configuration that gives the best
dynamic performance (SINAD, SFDR). To optimize dynamic
specifications, center the common-mode voltage of the analog
input at approximately by 2.5 V by connecting VINB to a low
impedance 2.5 V source. As described above, shorting the VREF
pin directly to the SENSE pin results in a 1 V reference voltage
and a 2 V p-p input span. The valid range for input signals is 1.5 V
to 3.5 V. The VREF pin should be bypassed to the REFCOM
pin with a 10 µF tantalum capacitor in parallel with a low induc-
tance 0.1 µF 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 19. In this case, the common-mode voltage,
V
tap to CML of the AD9221/AD9223/AD9220. 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 single-ended input
and thus becomes V
REV. E
CM
Figure 21. Internal Reference—2 V p-p Input Span,
V
, is set at midsupply by connecting the transformer’s center
2 VREF
Figure 22. Internal Reference—2 V p-p Input Span,
V
CM
CM
0V
= 1 V, or 5 V p-p Input Span, V
3.5V
1.5V
= 2.5 V
2.5V
10 F
CM
SHORT FOR 0V TO 2V
SHORT FOR 0V TO 5V
– VREF/2 to V
0.1 F
10 F
INPUT SPAN
INPUT SPAN
1V
0.1 F
VINA
VINB
VREF
SENSE
REFCOM
CM
CM
+ VREF/2.
CM
= 2.5 V
AD9221/
AD9223/
AD9220
VINA
VINB
VREF
SENSE
REFCOM
= 2.5 V
AD9221/
AD9223/
AD9220
–19–
Resistor Programmable Reference
Figure 23 shows an example of how to generate a reference
voltage other than 1 V or 2.5 V with the addition of two external
resistors and a bypass capacitor. Use the equation,
to determine appropriate values for R1 and R2. These resistors
should be in the 2 kΩ to 100 kΩ range. For the example shown,
R1 equals 2.5 kΩ and R2 equals 5 kΩ. 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 stability, place a
0.1 µF 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 × VREF.
Alternatively, the common-mode voltage can be set to VREF 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 µF tantalum capacitor in parallel with a low inductance
0.1 µF ceramic capacitor.
USING AN EXTERNAL REFERENCE
Using an external reference may enhance the dc performance of
the AD9221/AD9223/AD9220 by improving drift and accuracy.
Figures 24 through 26 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 internal reference amplifier.
Internal
AD589
AD1580
REF191
Internal
REF192
REF43
AD780
Figure 23. Resistor Programmable Reference—3 V p-p
Input Span, V
10 F
4V
1V
2.5V
Output
Voltage
1.00
1.235
1.225
2.048
2.50
2.50
2.50
2.50
Table III. Suitable Voltage References
CM
0.1 F
VREF
= 2.5 V
AD9221/AD9223/AD9220
Drift
(ppm/ C)
26
10–100
50–100
5–25
26
5–25
10–25
3–7
R1
2.5k
R2
5k
=
1
V
×
C1
0.1 F
(
1
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
R
1
VINB
VINA
VREF
SENSE
REFCOM
/
R
2
)
AD9220
Operating
Current
N/A
50
50
45
N/A
45
600
1000
( A)