Datasheet

UG-257 Evaluation Board User Guide
Rev. 0 | Page 4 of 20
NOISE TEST
Header J3 allows the user to perform noise testing of the
AD7195. With all links in the vertical position (see Figure 2),
the analog and reference inputs are applied to the AD7195 as
shown in Figure 3.
AV
DD
AIN1 AIN2 AINCOM AGND REF– REF+ VREF
J3
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Figure 2. Link Positions for Noise Testing
100Ω
1kΩ
1kΩ
AV
DD
AV
DD
AD7195
REFIN(+)
AIN1
AIN2
AINCOM
REFIN(–)
09727-003
Figure 3. Noise Test Connections
As per Figure 3, inserting the links in Header J3 connects a
resistor network to the AD7195. The reference to the ADC is
provided by AV
DD
. The resistor divider generates a bias voltage
of AV
DD
/2 approximately. Channel AIN1-AIN2 is connected to
this voltage, conversions can be performed using this external
short to measure the rms noise, peak-to-peak noise, peak-to-
peak resolution.
USING AN ABSOLUTE REFERENCE
An ADR421 is included on the AD7195 evaluation board so
that the part can also be evaluated using an absolute reference.
The reference can be connected to the REFIN pins of the
AD7195 by connecting the links of J3 as shown in Figure 4.
AV
DD
AIN1 AIN2 AINCOM AGND REF– REF+ VREF
J3
09727-004
Figure 4. Connecting an Absolute Reference to the AD7195
CONNECTING THE AD7195 TO AN EXTERNAL
MICROCONTROLLER
The AD7195 evaluation board can be connected to an external
microcontroller using Header J2. With all links in place, the
AD7195 is connected to the on-board microcontroller. How-
ever, with these links removed, the AD7195 is disconnected
from the evaluation board microcontroller. The user can
then use a header to interface the AD7195 to the external
microcontroller.