Datasheet

UG-280 Evaluation Board User Guide
Rev. 0 | Page 4 of 20
NOISE TEST
Header J3 allows the user to perform noise testing of the
AD7191. With all links in the vertical position (see Figure 2),
the analog and reference inputs are applied to the AD7191, as
shown in Figure 3.
AVDD AIN2 AIN1 AGND REF– REF+ VREF
J3
09880-002
Figure 2. Link Positions for Noise Testing
100Ω
1kΩ
1kΩ
AV
DD
A
V
DD
AD7191
REFIN(+)
AIN1
AIN2
REFIN(–)
09880-003
Figure 3. Noise Test Connections
As shown in Figure 3, inserting the links in Header J3 connects
a resistor network to the AD7191. The reference to the ADC is
provided by AV
DD
. The resistor divider generates a bias voltage
of approximately AV
DD
/2. Channel AIN1 and Channel AIN2 are
connected to this voltage. Thus, conversions can be performed
using this external short to measure the rms noise, peak-to-peak
noise, and peak-to-peak resolution. The ADC is configured
using the DIP switch (S6) on the board. The AD7191 should be
configured as follows:
Output Data Rate = 10 Hz
Gain = 128
Channel = AIN1 − AIN2
Figure 4 shows the positions of the switches on S6.
S6
ODR2
ODR1
CLKSEL
PGA1
CHAN
TEMP
PGA2
ONOFF
09880-004
Figure 4. Switch S6 Positions
USING AN ABSOLUTE REFERENCE
An ADR421 is included on the AD7191 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
AD7191 by connecting the links of Header J3 as shown in
Figure 5.
AVDD AIN1 AIN2 AGND REF– REF+ VREF
J3
09880-005
Figure 5. Connecting an Absolute Reference to the AD7191
CONNECTING THE AD7191 TO AN EXTERNAL
MICROCONTROLLER
The AD7191 evaluation board can be connected to an external
microcontroller using Header J2. With all links in place, the
AD7191 is connected to the on-board microcontroller. However,
with these links removed, the AD7191 is disconnected from
the evaluation board microcontroller. The user can then use a
header to interface the AD7191 to the external microcontroller.