UG-478 Datasheet, PDF (8/40 Pages) Analog Devices – Evaluation Board for the AD7176-2—24-Bit, 250 kSPS Sigma-Delta ADC with 20 μs Settling

UG-478
REFERENCE OPTIONS
The EVAL-AD7176-2SDZ includes an external 5 V reference (the
ADR445) and an internal 2.5 V reference. The default operation
is to use the external reference input, which is set to accept the 5 V
ADR445 on the evaluation board.
The reference used for a conversion is selected by choosing the
reference in the SETUPCONx registers associated with Setup 1,
Setup 2, Setup 3, and Setup 4.
Switch between using the internal reference and external reference
by accessing the AD7176-2 register map via the evaluation soft-
ware. Figure 3 shows how to select the reference source for
Setup 1, Setup 2, Setup 3, and Setup 4. Figure 4 shows the
ADCMODE register setting that enables the internal reference.
Figure 3. Selecting the Reference Source for
Setup 1, Setup 2, Setup 3, and Setup 4
Evaluation Board User Guide
Figure 4. Turning On the Internal 2.5 V Reference
USING THE ON-BOARD AMPLIFIERS
The AD7176-2 evaluation board contains three front-end configu-
rations. The AD8656 is provided for buffering the analog inputs
of the AD7176-2. By default, it is configured for a gain of 2, and
the front-end is selected on the evaluation board. The ADA4940-1
amplifier provides a single-ended to differential driver, whereas
the AD8475 is configured to operate as an attenuating single-ended
to differential driver. Figure 5 shows the location of the R and C
components on the AD7176-2 evaluation board. Figure 6 and
Figure 7 highlight the R and C components that are populated
on the board for each amplifier, and Table 5 to Table 7 list the
component values.
Figure 5. Identification of R/C Components for the Amplifiers
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