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4
Power Supplies
5
Using the EVM
5.1
Reference Design
Power Supplies
The EVM accepts four power supplies
•
A differential (
±
) dc supply for the dual-supply op amps. The maximum recommended voltage is
±
15
Vdc
•
A 5.0 V dc supply for the analog section of the board (A/D + Reference).
•
A 5.0 V or +3.3 V dc supply for digital section of the board (A/D + buffers).
There are two ways to provide these voltages. The first is to connect the voltages to the test points listed
in
Table 4
.
Table 4. Power Supply Test Points
Test Point
Signal
Description
TP1
+VA
C15.0 V dc supply for amplifier
TP2
–VA
Connect –15.0 V dc supply for amplifier
TP3
+BVDD
Apply +3.3 V dc or +5.0 V dc. See ADC data sheet for full range.
TP4
+AVCC
Apply +5.0 V dc
The second is to use the power connector J3, and derive the voltages elsewhere.
Table 5
gives the pinout
for J3. If using this connector, set W1 jumper to c3.3VD or +5VD from J3 to +BVDD. Shunt pins
1-2 to 5VD, or pins 2-3 to 3.3VD as the source for the digital-buffer-voltage supply
(+BVDD).
Table 5. Power Connector (J3) Pin Out
Signal
J1 Pin
Signal
+VA(+15V)
1
2
–VA(–15 V)
+5VA
3
4
N/C
DGND
5
6
AGND
N/C
7
8
N/C
+3.3VD
9
10
+5VD
The ADS8372EVM serves three functions:
1. As a reference design
2. As a prototype board
3. As a software test platform
As a reference design, the ADS8372EVM contains the essential circuitry to showcase the analog-to-digital
converter. This essential circuitry includes the input amplifier, reference circuit, and buffers. The EVM
analog-input circuit is optimized for a 100-kHz input signal; therefore, users may need to adjust the
resistor and capacitor values to accommodate higher frequencies. In ac-type applications where signal
distortion is concern, polypropylene or C0G type capacitors are recommended for use in the signal path.
Typical fully-differential amplifiers configured for single-ended in to differential out can distort the signal in
an attempt to equalize the input pins. This distortion is specially evident when step inputs are applied.
Therefore, users who will be applying a step input to the converter should use discrete amplifiers for the
single-ended-to-differential conversion of the signal. The Differential Input, Differential Output Configur-
ation circuit shown in the Theory of Operation section of the ADS8372 datasheet (literature number
SLAS451) can be used. In applications where the input is continuous, the single amplifier solution using
the THS4131, can effectively drive the converter inputs.
SLAU160 – July 2005
ADS8372EVM
5