EVAL-AD7472_15 Datasheet, PDF (3/20 Pages) Analog Devices – Evaluation Board for 10-/12-Bit High Speed, Low Power ADCs

EVAL-AD7470/AD7472
EVALUATION BOARD HARDWARE
POWER SUPPLIES
When using this evaluation board with the EVAL-CONTROL
BRD2 all supplies are provided from the EVAL-CONTROL
BRD2 through the 96-way connector.
When using the board as a standalone unit, external supplies
must be provided. This evaluation board has five power supply
inputs: VDD, AGND, VSS, VDRIVE, and DGND. Connect
+5 V to the VDD input to supply the AVDD and DVDD pins on
the AD7470/AD7472, the AD780 voltage reference, the positive
supply pin of all three op amps, and the digital control logic.
Connect 0 V to the AGND input. Connect −5 V to the VSS
input to supply the negative supply pins on all three op amps.
The VDRIVE input can be used to provide an external voltage
for the output drivers on the AD7470/AD7472. If an external
VDRIVE is supplied, it is referenced to the DGND input, which
should be tied to 0 V. The supplies are decoupled to the relevant
ground plane with 47 μF tantalum and 0.1 μF multilayer
ceramic capacitors at the point where they enter the board. The
supply pins of the op amps and reference are also decoupled to
AGND with a 10 μF tantalum and a 0.1 μF ceramic capacitor.
The AVDD supply pin is decoupled to AGND with 10 μF tanta-
lum and 0.1 μF multilayer ceramic capacitors. The AD7470/
AD7472 DVDD and VDRIVE pins are decoupled to AGND with
10 μF tantalum capacitors and to DGND with 0.1 μF multilayer
ceramic capacitors.
Extensive ground planes are used on this board to minimize
the effect of high frequency noise interference. There are two
ground planes, AGND and DGND, that are connected at one
location close to the AD7470/AD7472.
ANALOG INPUT
The analog input portion of this evaluation board accommo-
dates unipolar and bipolar signals. Unipolar signals within the
AD7470/AD7472 analog input signal range from 0 V to 2.5 V
and are connected via SK5. They are then buffered by the
on-board buffer before being applied to the VIN pin of the
AD7470/AD7472. Bipolar signals are connected via SK3 and
are biased up by the on-board bias-up buffer circuit before
being applied to the VIN pin of the AD7470/AD7472. The input
impedance of the bias-up circuit is 50 Ω, which is determined
by the value of R7. The input impedance may be modified by
removing/changing the value of R7. To obtain optimum perfor-
mance from this evaluation board, the use of an impedance
matched, passive filter is recommended before the analog signal
is applied to the evaluation board. For example, when using a
100 kHz input tone, a 100 kHz 50 Ω filter from TTE (part
number KC5-100K-15K-50-720B) is suitable.
R8 POTENTIOMETER (50 kΩ)
This variable resistor is used to trim the dc bias voltage applied
to the optional analog input bias-up circuit. This bias voltage is
factory preset to 1.25 V, which biases a bipolar signal to swing
around the midpoint of the analog input range (0 V to 2.5 V).
If any adjustment is required, the user can use the histogram
window in the evaluation board software to analyze the dc vol-
tage variation while adjusting the trimmer potentiometer. To
view this properly, an analog input signal should not be applied
to the board. Under normal operation, this potentiometer should
not be adjusted as it is preset for optimum performance.
LINK AND SWITCH OPTIONS
There are 11 link options, which must be set for the required
operating setup before using the evaluation board. The
functions of these options are outlined in Table 1.
Table 1.
Link No.
LK1
LK2
LK3
Function
This link is used to select the dc bias voltage to be applied to the optional VIN bias-up circuit.
If the user is using the bias-up circuit, this link must be inserted which applies the 2.5 V reference voltage to the bias-up circuit.
This causes a bipolar signal (applied to the bipolar VIN input socket) to be biased up around +1.25 V before it is applied to the
AD7470/AD7472 VIN pin (see also LK10).
If the bias up circuit is not being used, this link should be removed.
This link must be in Position A if external power supplies are being used. In this position, the control logic is being powered by
the voltage applied to the VDD input.
When power is being supplied from the EVAL-CONTROL BRD2, this link can be moved to Position B if the user wants to drive the
control logic from a separate +5 V, which is generated, on the EVAL-CONTROL BRD2.
This link option selects the source of the CLKIN input.
In Position A, the CLKIN input is provided by the EVAL-CONTROL BRD2.
In Position B, the CLKIN input is provided via the on-board 25 MHz oscillator.
In Position C, an external CLKIN signal must be provided via the external socket, SK1.
When using the on-board generated burst clock, this link must be in Position D.
Rev. C | Page 3 of 20