AD9266BCPZ-40 Analog Devices Inc, AD9266BCPZ-40 Datasheet - Page 19

• Manufacturer Part Number: AD9266BCPZ-40
• Description: 16 Bit, 40 MSPS 1.8V Single ADC
• Manufacturer: Analog Devices Inc

Specifications of AD9266BCPZ-40

• Number Of Bits: 16
• Sampling Rate (per Second): 40M
• Data Interface: Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 82mW
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-LFCSP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

VOLTAGE REFERENCE
A stable and accurate 1.0 V voltage reference is built into the
AD9266. The VREF can be configured using either the internal
1.0 V reference or an externally applied 1.0 V reference voltage.
The various reference modes are summarized in the sections that
follow. The Reference Decoupling section describes the best
practices for PCB layout of VREF.
Internal Reference Connection
A comparator within the AD9266 detects the potential at the
SENSE pin and configures the reference into two possible modes,
which are summarized in Table 10. If SENSE is grounded, the
reference amplifier switch is connected to the internal resistor
divider (see Figure 42), setting VREF to 1.0 V.
If the internal reference of the AD9266 is used to drive multiple
converters to improve gain matching, the loading of the reference
by the other converters must be considered. Figure 43 shows
how the internal reference voltage is affected by loading.
Table 10. Reference Configuration Summary
Selected Mode
Fixed Internal Reference
Fixed External Reference
1.0µF
Figure 42. Internal Reference Configuration
0.1µF
SENSE
VREF
VIN+
VIN–
SELECT
LOGIC
SENSE Voltage (V)
AGND to 0.2
AVDD
ADC
0.5V
CORE
ADC
Resulting VREF (V)
1.0 internal
1.0 applied to external VREF pin
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External Reference Operation
The use of an external reference may be necessary to enhance
the gain accuracy of the ADC or improve thermal drift charac-
teristics. Figure 44 shows the typical drift characteristics of the
internal reference in 1.0 V mode.
When the SENSE pin is tied to AVDD, the internal reference is
disabled, allowing the use of an external reference. An internal
reference buffer loads the external reference with an equivalent
7.5 kΩ load (see Figure 28). The internal buffer generates the posi-
tive and negative full-scale references for the ADC core. Therefore,
the external reference must be limited to a maximum of 1.0 V.
–0.5
–1.0
–1.5
–2.0
–2.5
–3.0
–1
–2
–3
–4
–5
–6
0
4
3
2
1
0
–40
0
0.2
Figure 43. V
–20
0.4
Resulting Differential Span (V p-p)
2.0
2.0
Figure 44. Typical V
0.6
0
V
LOAD CURRENT (mA)
REF
REF
TEMPERATURE (°C)
Accuracy vs. Load Current
0.8
INTERNAL V
ERROR (mV)
20
1.0
1.2
REF
REF
40
Drift
= 0.995V
1.4
1.6
60
1.8
AD9266
80
2.0