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Analog Devices Semiconductor Electronic Components Datasheet

AD7492 Datasheet

Evaluation Board for 12-bit high speed/ low power/ successive-approximation ADC

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= EvaluationBoardfor12-bithighspeed,
low power, successive-approximation ADC
EVAL-AD7492CB
FEATURES
Full-Featured Evaluation Board for the AD7492
EVAL-CONTROL BRD2 Compatible
Stand Alone Capability
On-Board Analog Buffering and Reference
Optional On-Board Analog Bias-Up Circuit
Various Linking Options
PC Software for Control and Data Analysis when used
with EVAL-CONTROL BRD2
Interfacing to this board is through a 96-way connector. This
96-way connector is compatible with the EVAL-CONTROL
BRD2 which is also available from Analog Devices. External
sockets are provided for the CONVST input and the VIN
inputs.
OPERATING THE AD7492 EVALUATION BOARD
Power Supplies
When using this evaluation board with the EVAL-CON-
TROL BRD2, all supplies are provided from the EVAL-
CONTROL BRD2 through the 96 way connector.
INTRODUCTION
This Technical Note describes the evaluation board for the
AD7492 12-bit, high speed, low power, internal reference
and clock, successive approximation A/D converter that
operates from a single 2.7 V to 5.25 V supply. Full data on
the AD7492 is available in the AD7492 data sheet available
from Analog Devices and should be consulted in conjunction
with this Technical Note when using the Evaluation Board.
On-board components include an AD780 which is a pin
programmable +2.5 V or +3 V ultra high precision bandgap
reference, two AD797 op-amps used to buffer the analog
input, and an OP07 op-amp used to buffer the DC bias
voltage applied to the optional analog input bias-up circuit.
There are various link options which are explained in detail
on page 2.
When using the board as a stand alone unit, external supplies
must be provided. This evaluation board has five power
supply inputs: VDD, AGND, VSS, VDRIVE and DGND. +5 V must
be connected to the VDD input to supply the AVDD and DVDD
pins on the AD7492, the AD780 voltage reference, the
positive supply pin of all three op-amps and the digital
control logic. 0 V is connected to the AGND input. -5 V must
be connected 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
AD7492. 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 47µF tantalum
and 0.1µF multilayer ceramic capacitors at the point where
they enter the board. The supply pins of the op-amps and
FUNCTIONAL BLOCK DIAGRAM
Unipolar
Ain
Buffe r
AD7492 ADC
Bipolar
Ain
B i a s-u p
buffer
External
Reference
Vin
Ref Out
Data Bus
Control Lines
Power Supply Circuit
REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood. MA 02062-9106, U.S.A.
Tel: 617/329-4700
Fax: 617/326-8703


Analog Devices Semiconductor Electronic Components Datasheet

AD7492 Datasheet

Evaluation Board for 12-bit high speed/ low power/ successive-approximation ADC

No Preview Available !

EVAL-AD7492CB
reference are also decoupled to AGND with a 10µF tantalum and a 0.1µF ceramic capacitor. The AD7492 AVDD supply pin is
decoupled to AGND with 10uF tantalum and 0.1µF multilayer ceramic capacitors. The AD7492 DVDD and VDRIVE pins are
decoupled to AGND with 10uF tantalum capacitors and to DGND with 0.1µF 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. These are connected at one location close to the AD7492.
Analog Input Section
The analog input section of this evaluation board accommodates unipolar and bipolar signals. Unipolar signals within the
AD7492 analog input signal range of 0 V - 2.5 V are connected via SK1. They are then buffered by the on-board buffer before
being applied to the VIN pin of the AD7492. 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 AD7492. The input impedence of the bias-up circuit is 50which
is determined by the value of R7. The input impedence may be modified by removing/changing the value of R7. To obtain
optimum performance from this evaluation board the use of an impedence matched, passive filter is recommended before the
analog signal is applied to the evaluation board. For example, when using a 100KHz input tone, a 100KHz 50filter from
TTE (part number KC5-100K-15K-50/50-720B) is suitable.
R13 Potentiometer (50Kohm)
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 - 2.5 V).
If any adjustment is required, the user can use the histogram window in the eval-board software to analyze the DC voltage
variation while adjusting the trim pot. To view this properly, an analog input signal should not be applied to the board. Under
normal operation this pot should not be adjusted as it is preset for optimum performance.
LINK AND SWITCH OPTIONS
There are 12 link options which must be set for the required operating setup before using the evaluation board. The functions
of these options are outlined below.
Link No.
Function.
LK1
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 will apply 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 AD7492 VIN pin. - see also LK10 (below).
When this link is in position "A" the bias-up circuit is supplied by the AD7492 internal reference.
When this link is in position "B" the bias-up circuit is supplied by the AD780 external reference.
If the bias up circuit is not being used this link should be removed.
LK2
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.
LK3
This link option selects the sleep mode that the AD7492 can be put into.
When this link is in position "A" the part goes into full sleep when low power operation is selected.
When this link is in position "B" the part goes into partial sleep when low power operation is selected.
LK4
This link option selects the source of the CONVST input.
When this link is in position "A" the CONVST input is provided by the EVAL-CONTROL BRD2.
When this link is in position "B" the CONVST input is provided via the external socket, SK2.
LK5
This link option selects the source of the RD input.
When this link is in position "A" the RD input is provided by the EVAL-CONTROL BRD2.
When this link is in position "B" the RD input is tied to GND.
LK6
This link option selects the source of the CS input.
When this link is in position "A" the CS input is provided by the EVAL-CONTROL BRD2.
When this link is in position "B" the CS input is tied to GND.
LK7
This link option sets the voltage applied to the VDRIVE pin on the AD7492.
When this link is in position "A", VDRIVE is connected directly to the DVDD pin.
When this link is in position "B", an external voltage must be applied to the VDRIVE pin Via J3.
LK8
LK9
This link selects the source of the VDD supply.
When this link is in position "A" VDD must be supplied from an external source via J2.
When this link is in position "B" VDD is supplied from the EVAL-CONTROL BRD2.
This link selects the source of the VSS supply.
When this link is in position "A" VSS must be supplied from an external source via J2.
When this link is in position "B" VSS is supplied from the EVAL-CONTROL BRD2.
–2–
REV. A


Part Number AD7492
Description Evaluation Board for 12-bit high speed/ low power/ successive-approximation ADC
Maker Analog Devices
Total Page 14 Pages
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