Analog Devices AD7495CB, AD7475CB Datasheet
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Tel: 617/329-4700 Fax: 617/326-8703
REV. 0
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 for 1MSPS, 12-Bit ADC
EVAL-AD7475/AD7495CB
FUNCTIONAL BLOCK DIAGRAM
FEATURES
Full-Featured Evaluation Board for the AD7475/95
EVALUATION-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 EVALUATION-BOARD CONTROLLER
Patchwork Area for User Expansion
INTRODUCTION
This Technical Note describes the evaluation board for
the AD7475/AD7495 which is a fast 12-bit high speed, low
power successive-approximation ADCs. The parts operate
from a sinlge 2.7 V to 5.25 V power supply and feature
throughput rates up to 1 MSPS. Full data on the
AD7475/AD7495 is available in the AD7475/AD7495
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 +2.5V or +3V ultra high precision
bandgap reference and an AD711 op-amp used to buffer
the analog input. 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 EVALUATION-BOARD CONTROLLER which is also available
from Analog Devices. External sockets are provided for
the REFIN input and the VIN input.
OPERATING THE AD7475/AD7495 EVALUATION
BOARD
Power Supplies
When using this evaluation board with the EVALUATION-BOARD CONTROLLER all supplies are provided from the EVALUATION-BOARD
CONTROLLER through the 96 way connector.
When using the board as a stand alone unit external supplies must be provided. This evaluation board has six
power supply inputs: V
DD
, A
GND
, +12V, -12V, A
GND
, 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
AD7475/AD7495 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 AD7475/AD7495 AV
DD
supply pin is decoupled to A
GND
with 10 µF tantalum and
0.1µF multilayer ceramic capacitors.
Extensive ground planes are used on this board to mini-
mize the effect of high frequency noise interference. There
are two ground planes, A
GND
and D
GND
. These are con-
nected at one location close to the AD7475/AD7495.
AD7475/A
D7495
EXTERNAL
REFERENCE
ANALOG
INPUT
CS
SDATA
SCLK
Vdd
Vdrive
Vdd
BIAS UP CIR-
CUIT
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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 connect the input of the AD711 op-amp to ground if the user needs to do this.
When this link is in position "A" a signal applied to the AIN socket is routed to the input of the AD711 opamp. This is the normal application for this link.
When this link is in position "B", the input of the AD711 op-amp is tied to GND.
LK2
This link option controls the program pin of the AD780 voltage reference.
When this link is "inserted" the AD780 output is set to +3.0 V.
When this link is "removed" the AD780 output is set to +2.5 V
LK3 This link is used to select the source of the reference voltage applied to the AD7475 REFIN pin.
When this link is in position "A", the AD780 provides the 2.5V reference to the AD7475.
When this link is in position "B" an external reference must be supplied to the AD7475 via J5.
For the AD7495 this pin must be removed
LK4 This link selects the source of the V
DD
+5V supply.
When this link is in position "A" the +5V is supplied from an exteranl source via J6.
When this link is in position "B" the +5V must be supplied from the EVALUATION-BOARD
CONTROLLER
LK5 This link option selects the source of the VDRIVE input.
When this link is in position "A" the VDRIVE supply voltage is provided from VDD.
When this link is in position "B" the VDRIVE supply voltage is provided from the EVALUATION-BOARD
CONTROLLER.
When this link is in position "C" an external VDRIVE supply voltage must be supplied via J7.
LK6 This link option is used to select the source of the +12V supply
In position A, the +12V is supplied from the EVALUATION-BOARD CONTROLLER through the 96 way
connector.
In position B, the +12V is supplied from an external source through the power connector, J8.
LK7 This link option is used to select the source of the -12V supply.
In position A, the -12V is supplied from the EVALUATION-BOARD CONTROLLER through the 96 way
connector.
In position B, the -12V is supplied from an external source through the power connector, J8.
LK8 This link option sets the dc bias voltage applied to the optional bais-up/filter circuit.
When the link is in position "A", the bias voltage is set to the same level as the voltage that is applied to the
REF IN on the AD7475 and the REF OUT pin on the AD7495. In this configuration a bipolar anlag input
applied to the Vin SMB socket as a unipolar signal biased around Vref/2. When in position "B", the bias
voltage is set to A
GND
. In this configuration the bias up circuit is not used.
LK9 This link option adds a 50 Ohm termination to AGND at the Ain socket. In most applications this link will
be left unconnected. If a 50 Ohm termination is required, this link should be inserted.
LK10 This link option adds a 50 Ohm termination to AGND at the Vin socket. In most applications this link will
be left unconnected. If a 50 Ohm termination is required, this link should be inserted.
LK11, LK12 When both these links are in position "A", for slower SCLK frequencies, giving valid data on the rising edge.
When both these links are in position "B", for fast SCLK frequencies, giving valid data on the falling edge,
the SCLK signal is connected directly to the AD7898 SCLK pin. This is the normal position for these 2 link
options.
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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 sent out.
Table I. Initial Link and Switch Positions
Link No. Position Function.
LK1 A Ain is tied to the input of the AD711 buffer op-amp.
LK2 removed AD780 is set to provide a + 2.5 V reference.
LK3 A The on-board AD780 voltage reference supplies the REFIN pin of the AD7475.
removed The internal + 2.5V reference on the AD7495 is used on the AD7495 control
board
LK4 B V
DD
(+5V) supplied by the EVALUATION-BOARD CONTROLLER via J5.
LK5 A VDRIVE pin of the AD7475/AD7495 is connected to V
DD
(+5V)
LK6 A +12V supplied from EVAL-CONTROL BOARD via J5.
LK7 A -12V supplied from EVAL-CONTROL BOARD via J5.
LK8 A Vref is chosen as the dc bias voltage for the bias-up circuit.
LK9 removed 50 Ohm termination is not selected.
LK10 removed 50 Ohm termination is not selected.
LK11, LK12 B SCLK signal from EVALUATION-BOARD CONTROLLER is not inverted, (for
faster values of SCLK).
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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
EVAL-CONTROL BOARD or other system. The pinout
for the J5 connector is shown in Figure 1 and its pin designations are given in Table II.
1
32
1
32
A
B
C
Figure 1. Pin Configuration for the 96-Way
Connector, J5
96-Way Connector Pin Description
DR0 DATA RECEIVE ONE: Serial Data from the
AD7898 is provided at this output. Sixteen bits of
data are provided with four leading zeroes followed by twelve bits of conversion data which is
provided MSB first.
SCLK0 SERIAL CLOCK ZERO: This continuous clock
is connected to the SCLK pin of the AD7898 via
LK7 to obtain serial data from the AD7898.
TFS0 TRNSMIT FRAME SYNC ZERO,
RFS0 RECEIVE FRAME SYNC ZERO: Both of these
inputs are conncected to the AD7898 CS/
CONVST pin via LK5 to initiate conversions
and to frame the serial data tansfer.
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 AV
DD
supply line on the board via LK4.
+12V +12V Supply. This line is connected to the +12V
supply line on the board via LK8.
-12V -12V Supply. This line is connected to the -12V
supply line on the board via LK9.
Table II. 96-Way Connector Pin Functions.
ROW A ROWB ROWC
1
2
3
4 DGND DGND DGND
5 DR0
6 TFS0 RFSO
7 SCLK0 SCLK0
8
9
10
11
12 DGND DGND DGND
13
14
15
16 DGND DGND DGND
17
18
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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