Analog Devices AD7899CB Datasheet
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Tel: 617/329-4700 Fax: 617/326-8703
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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.
a
Evaluation Board 400kSPS, 14-Bit ADC
EVAL-AD7899CB
Fig. 1: FUNCTIONAL BLOCK DIAGRAM
FEATURES
Full-Featured Evaluation Board for the AD7899
Eval-Board Controller Compatible
Stand Alone Capability
On-Board Analog Buffering and Reference
Various Linking Options
PC Software for Control and Data Analysis when used
with Eval-Board Controller
INTRODUCTION
This Technical Note describes the evaluation board for the
AD7899 high speed, low power, 14-bit A/D converter that
operates from a single 5 V supply. Full data on the AD7899
is available in the AD7899 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 +2.5V
ultra high precision bandgap reference and an op-amp for the
analog inputs. There are various link options which are
explained in detail on page 2.
Interfacing to this board is through a 96-way connector. This
96-way connector is compatible with the EVAL-BOARD
CONTROLLER which is also available from Analog Devices. External sockets are provided for the optional, external, CONVST and CLKIN and V
DRIVE
inputs and the
VIN1-VIN4 inputs.
OPERATING THE AD7899 EVALUATION BOARD
Power Supplies
When using this evaluation board with the EVAL-BOARD
CONTROLLER all supplies are provided from the EVALBOARD CONTROLLER through the 96 way connector.
When using the board as a stand alone unit external supplies
must be provided. This evaluation board has seven power
supply inputs: V
DD
, A
GND
, +12V, -12V, A
GND
, V
DRIVE
and
D
GND
. If the evaluation board is used in stand-alone mode
+5V must be connected to the V
DD
input to supply the
AD7899 V
DD
pin and the AD780 voltage reference. +12V and
-12V are used to supply the op-amps. The V
DRIVE
pin can be
driven by a voltage between +3V and +5V allowing the
evaluation board to be connected to both +3V and +5V
systems. The supplies are decoupled to the relevant ground
plane with 10µF tantalum and 0.1µF multilayer ceramic
capacitors at the point where they enter the board. The supply
pins of all the op-amps and reference are also decoupled to
A
GND
with 10µF tantalum and a 0.1µF ceramic capacitor. The
AD7899 AV
DD
supply pin is decoupled to A
GND
with 47uF
tantalum and 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, A
GND
and D
GND
. These are connected at one
location close to the AD7899.
AD7899
ANALOG
SIGNAL
CONDITIONING
EXTERNAL
REFERENCE
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GI
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96
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Link and Switch Options
There are 9 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 option selects the input range of the ADC. The position of this link is determined by the input
range required by the user. Please refer to the AD7899 data sheet for more information.
When this link is in position "A" V
INB
is connected to V
INA
.
When this link is in position "B" V
INB
is connected toAGND.
LK2 This link selects the reference source for the AD7899.
When a link is in position "A" the AD780 is selected as the reference source.
When a link is in position "B" an external voltage applied to SK7 is selected as the reference source.
When the link is removed completly the internal reference of the AD7899 is used as the reference source.
LK3 This link selects the source of the +12V supply.
When this link is in position "A" an external +12V must be connected to J2-1.
When this link is in position "B" the EVAL-BOARD CONTROLLER will provide the +12V supply
LK4 This link selects the source of the VDD supply.
When this link is in position "A" an external +5V must be connected to J2-2.
When this link is in position "B" the EVAL-BOARD CONTROLLER will provide the +5V supply
LK5 This link selects the source of the -12V supply.
When this link is in position "A" an external -12V must be connected to J2-4.
When this link is in position "B" the EVAL-BOARD CONTROLLER will provide the -12V supply
LK6 This link selects the source of the V
DRIVE
supply.
When this link is in position A the VDD supply is used as the V
DRIVE
supply.
When this link is in position B the DVDD supply of the EVAL-BOARD CONTROLLER is used as the
V
DRIVE
supply.
When this link is in position C an external supply on SK6 is used as the V
DRIVE
supply.
LK7 This link is used to select the source of the Conversion Start signal.
When this link is in position "A" the CONVST signal is generated by the EVAL-BOARD CONTROLLER.
When this link is in position "B" the CONVST signal is generated by an external signal connected to SK2.
LK8 This link selects the source of the CLKIN signal for the AD7899.
When this link is in position "A" the CLKIN signal is provided by the EVAL-BOARD CONTROLLER.
When this link is in position "B" the CLKIN signal can be provided by a signal applied to SK3. If no
signal is applied to SK3 the pin is pulled low and the internal oscillator is is used to control the conversion.
LK9 This link sets the logic level of the STBY pin.
When a link is in position "A" the STBY pin is controlled by the FL1 flag pin of the EVAL-BOARD
CONTROLLER.
When a link is in position "B" the STBY pin is tied to VDD and the part is in normal operating mode.
When a link is in position "C" the STBY pin is tied to DGND and the part is in standby mode.
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SET-UP CONDITIONS
Care should be taken before applying power and signals to the evaluation board to ensure that all link positions are as
per the required operating mode. Table I shows the position in which all the links are set when the evaluation board is
shipped. The board is compatible with the EVAL-BOARD CONTROLLER when shipped.
Table I. Initial Link and Switch Positions
Link No. Position Function.
LK1 B The largest voltage range for the part is selected.
LK2 A The AD780 is selected as the reference source for the AD7899.
LK3-5 B The EVAL-BOARD CONTROLLER is used to provide the supply voltages for the
evaluation board.
LK6 A The V
DRIVE
pin is connected to the VDD supply.
LK7 B The CONVST signal is provided by the EVAL-BOARD CONTROLLER.
LK8 B The CLKIN can be supplied either by an external signal connected to SK3 or by the
AD7899s internal oscillator.
LK9 B The STBY pin is tied to VDD
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EVALUATION BOARD INTERFACING
Interfacing to the evaluation board is via a 96-way connector,
J1. J1 is used to connect the evaluation board to the EVALBOARD CONTROLLER or other system. The pinout for
the J1 connector is shown in Figure 2 and its pin designations
are given in Table II.
1
32
1
32
A
B
C
Fig. 2. Pin Configuration for the 96-Way Connector, J1
96-Way Connector Pin Description
FL1 Flag one. This is a logic input and is connected
to the STBY pin of the AD7899. A logic high on
this pin allows normal operation of the AD7899.
A logic low on this pin puts the AD7899 into
standby mode.
D0-D13 Data Bit 0 to Data Bit 13. Bi-directional data
pins. These data bits provide the ADC conversion
results during a read operation.
RD Read. This is an active low logic input which is
used in conjunction with the CS pin to enable the
data outputs.
WR Write. A logic input. A rising edge on this input,
with
CS low and RD high latches the logic state
on D0-D3 into the channel select register. Software selection of channels is not supported by this
evaluation board.
CS Chip Select. An active low logic input. A low
level on this input selects the AD7899.
FL0 Flag zero. This logic input is connected to the
CONVST input of the AD7899 via LK7. A low
to high transition on this input puts all the track/
holds into their hold mode and starts conversion
on the selected channels. In addition the state of
the channel sequence selection is also latched on
the rising edge of this input
IRQ2 Interrupt Request 2. This is a logic output and is
connected to the BUSY logic output on the
AD7899. This output will go high on the rising
edge of CONVST and will return low when
conversion is completed on all selected channels.
DGND Digital Ground. These lines are connected to the
digital ground plane on the evaluation board. It
allows the user to provide the digital supply via
the connector along with the other digital signals.
AGND Analog Ground. These lines are connected to the
analog ground plane on the evaluation board.
AV
DD
Analog +5V Supply. These lines are connected to
the V
DD
supply line on the board via LK4.
+12V +12V Supply. This line is connected to the +12V
supply line on the board via LK3.
-12V -12V Supply. This line is connected to the -12V
supply line on the board via LK5.
Table II. 96-Way Connector Pin Functions.
ROW a RowB RowC
1 FL1
2D0
3 SCLK1 D1 SCLK1
4 DGND DGND DGND
5D2
6D3
7D4
8
9RD D5 WR
10 D6 CS
11 D7
12 DGND DGND DGND
13 D8
14 D9
15 D10
16 DGND DGND DGND
17 FL0 D11 IRQ2
18 D12 D13
19
20 DGND DGND DGND
21 AGND AGND AGND
22 AGND AGND AGND
23 AGND AGND AGND
24 AGND AGND AGND
25 AGND AGND AGND
26 AGND AGND AGND
27 AGND
28 AGND
29 AGND AGND AGND
30 -12V AGND +12V
31
32 AVDD AVDD AVDD
Note : The unused pins of the 96-way connector are not shown.
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