Texas Instruments Performance Development Kit for 18-Bit, 1 MSPS, Serial Interface SAR ADC ADS8881EVM-PDK ADS8881EVM-PDK Data Sheet
Product codes
ADS8881EVM-PDK
5V
5V
0.22
+
-
+
1k
1µF
+
-
+
OPA333
THS4281
10µF
1µF
20k
1k
1µF
Vref
4.5V from
REF5045
AINP
AINN
10000pF
10
10
-
+
+
-
10
10
1k
1k
1k
THS4521
Vocm =+2.25V
1k
-4.3V
+4.3V
0V
0.1V
4.3V
2.25V
0.1V
4.3V
2.25V
-4.3V
+4.3V
0V
5V
A0(+)
A0(-)
0V
+8.6V
EVM Analog Interface
2.2
Single Ended Signal Configuration
The ADS8881 can only convert single ended signals between 0 V and V
REF
. The THS4521 can condition a
single ended to a differential signal allowing a larger input voltage range for the EVM input A0(+). The
single ended signal range can be 0 V to 8.6 V or –4.3 V to 4.3 V to avoid saturating amplifier output. The
EVM A0(-) input should be grounded for single-ended signals as illustrated in
single ended signal range can be 0 V to 8.6 V or –4.3 V to 4.3 V to avoid saturating amplifier output. The
EVM A0(-) input should be grounded for single-ended signals as illustrated in
Figure 2. Single Ended Signal Example
2.3
Voltage Reference
Since the EVM is powered by a 5-V analog supply, the reference should be a value below 5 V. This EVM
uses a 4.5 V created by the on-board REF5045. Then, it is filtered by an RC filter of 160-Hz cutoff
frequency to minimize its noise contribution. Finally, the EVM is buffered by the THS4281, which can drive
the 10-
uses a 4.5 V created by the on-board REF5045. Then, it is filtered by an RC filter of 160-Hz cutoff
frequency to minimize its noise contribution. Finally, the EVM is buffered by the THS4281, which can drive
the 10-
μ
F required at the ADC reference (with 2 MHz of an effective bandwidth and 22-
μ
Vrms of total
noise). OPA333 and the additional feedback is optional, but it complements the THS4281 minimizing its
offset and drift.
offset and drift.
Figure 3. THS4281 Reference Driver with Complementary OPA333 for Drift and Offset Correction
5
SBAU211 – June 2013
ADS8881EVM-PDK
Copyright © 2013, Texas Instruments Incorporated