EVAL-AD7475
a Evaluation Board for 1MSPS, 12-Bit ADC
EVAL-AD7475/AD7495CB
FEATURES
OPERATING THE AD7475/AD7495 EVALUATION
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 EVALUA- TION-BOARD CONTROLLER which is also available from Analog Devices. External sockets are provided for the REFIN input and the VIN input.
BOARD
Power Supplies
When using this evaluation board with the EVALUA- TION-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: VDD, AGND, +12V, -12V, AGND, and DGND. If the evaluation board is used in stand-alone mode
+5V must be connected to the VDD input to supply the AD7475/AD7495 VDD pin and the AD780 voltage reference. +12V and -12V are used to supply the op-amps. The
VDRIVE 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 AGND with 10µF tantalum and a 0.1µF ceramic capacitor. The AD7475/AD7495 AVDD supply pin is decoupled to AGND with 10 µF 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, AGND and DGND. These are connected at one location close to the AD7475/AD7495.
FUNCTIONAL BLOCK DIAGRAM
ANALOG
INPUT
Vdd
AD7475/A
D7495 CS
SDATA
SCLK
Vdrive
EXTERNAL
REFERENCE
Vdd
BIAS UP CIR-
CUIT
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.
One Technology Way, P.O. Box 9106, Norwood. MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703
EVAL-AD7475/AD7495CB
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. |
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LK1 |
This link is used to connect the input of the AD711 op-amp to ground if the user needs to do this. |
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When this link is in position "A" a signal applied to the AIN socket is routed to the input of the AD711 op- |
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amp. This is the normal application for this link. |
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When this link is in position "B", the input of the AD711 op-amp is tied to GND. |
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LK2 |
This link option controls the program pin of the AD780 voltage reference. |
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When this link is "inserted" the AD780 output is set to +3.0 V. |
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When this link is "removed" the AD780 output is set to +2.5 V |
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LK3 |
This link is used to select the source of the reference voltage applied to the AD7475 REFIN pin. |
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When this link is in position "A", the AD780 provides the 2.5V reference to the AD7475. |
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When this link is in position "B" an external reference must be supplied to the AD7475 via J5. |
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For the AD7495 this pin must be removed |
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LK4 |
This link selects the source of the VDD +5V supply. |
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When this link is in position "A" the +5V is supplied from an exteranl source via J6. |
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When this link is in position "B" the +5V must be supplied from the EVALUATION-BOARD |
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CONTROLLER |
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LK5 |
This link option selects the source of the VDRIVE input. |
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When this link is in position "A" the VDRIVE supply voltage is provided from VDD. |
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When this link is in position "B" the VDRIVE supply voltage is provided from the EVALUATION-BOARD |
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CONTROLLER. |
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When this link is in position "C" an external VDRIVE supply voltage must be supplied via J7. |
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LK6 |
This link option is used to select the source of the +12V supply |
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In position A, the +12V is supplied from the EVALUATION-BOARD CONTROLLER through the 96 way |
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connector. |
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In position B, the +12V is supplied from an external source through the power connector, J8. |
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LK7 |
This link option is used to select the source of the -12V supply. |
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In position A, the -12V is supplied from the EVALUATION-BOARD CONTROLLER through the 96 way |
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connector. |
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In position B, the -12V is supplied from an external source through the power connector, J8. |
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LK8 |
This link option sets the dc bias voltage applied to the optional bais-up/filter circuit. |
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When the link is in position "A", the bias voltage is set to the same level as the voltage that is applied to the |
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REF IN on the AD7475 and the REF OUT pin on the AD7495. In this configuration a bipolar anlag input |
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applied to the Vin SMB socket as a unipolar signal biased around Vref/2. When in position "B", the bias |
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voltage is set to AGND. In this configuration the bias up circuit is not used. |
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LK9 |
This link option adds a 50 Ohm termination to AGND at the Ain socket. In most applications this link will |
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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 |
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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. |
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When both these links are in position "B", for fast SCLK frequencies, giving valid data on the falling edge, |
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the SCLK signal is connected directly to the AD7898 SCLK pin. This is the normal position for these 2 link |
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options. |
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– 2 – |
REV. 0 |
EVAL-AD7475/AD7495CB
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. |
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Table I. Initial Link and Switch Positions |
Link |
No. |
Position |
Function. |
LK1 |
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A |
Ain is tied to the input of the AD711 buffer op-amp. |
LK2 |
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removed |
AD780 is set to provide a + 2.5 V reference. |
LK3 |
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A |
The on-board AD780 voltage reference supplies the REFIN pin of the AD7475. |
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removed |
The internal + 2.5V reference on the AD7495 is used on the AD7495 control |
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board |
LK4 |
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B |
VDD (+5V) supplied by the EVALUATION-BOARD CONTROLLER via J5. |
LK5 |
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A |
VDRIVE pin of the AD7475/AD7495 is connected to VDD (+5V) |
LK6 |
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A |
+12V supplied from EVAL-CONTROL BOARD via J5. |
LK7 |
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A |
-12V supplied from EVAL-CONTROL BOARD via J5. |
LK8 |
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A |
Vref is chosen as the dc bias voltage for the bias-up circuit. |
LK9 |
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removed |
50 Ohm termination is not selected. |
LK10 |
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removed |
50 Ohm termination is not selected. |
LK11, LK12 |
B |
SCLK signal from EVALUATION-BOARD CONTROLLER is not inverted, (for |
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faster values of SCLK). |
REV. 0 |
– 3 – |
EVAL-AD7475/AD7495CB
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.
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Figure 1. Pin Configuration for the |
96-Way |
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Connector, J5 |
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96-Way Connector Pin Description |
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DR0 |
DATA RECEIVE ONE: Serial Data from the |
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AD7898 is provided at this output. Sixteen bits of |
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data are provided with four leading zeroes fol- |
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lowed by twelve bits of conversion data which is |
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provided MSB first. |
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SCLK0 |
SERIAL CLOCK ZERO: This continuous clock |
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is connected to the SCLK |
pin of the AD7898 via |
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LK7 to obtain serial data from the AD7898. |
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TFS0 |
TRNSMIT FRAME SYNC ZERO, |
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RFS0 |
RECEIVE FRAME SYNC ZERO: Both of these |
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inputs are conncected to the AD7898 CS/ |
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CONVST pin via LK5 to initiate |
conversions |
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and to frame the serial data tansfer. |
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DGND |
Digital Ground. |
These |
lines are |
connected to |
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the digital ground |
plane |
on |
the evaluation |
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board. It allows the user to provide the digital |
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supply via the connector along with the other |
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digital signals. |
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AGND |
Analog Ground. These lines are connected to |
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the analog ground plane on the evaluation |
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board. |
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AVDD |
Analog +5V Supply. These lines are connected |
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to the AVDD supply line on the board via LK4. |
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+12V |
+12V Supply. This line is connected to the +12V |
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supply line on the board via LK8. |
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-12V |
-12V Supply. This line is connected to the -12V |
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supply line on the |
board |
via |
LK9. |
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Table II. 96-Way Connector Pin Functions.
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ROW A |
ROWB |
ROWC |
1 |
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2 |
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3 |
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4 |
DGND |
DGND |
DGND |
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5 |
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DR0 |
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6 |
TFS0 |
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RFSO |
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7 |
SCLK0 |
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SCLK0 |
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8 |
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9 |
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10 |
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11 |
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12 |
DGND |
DGND |
DGND |
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14 |
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15 |
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16 |
DGND |
DGND |
DGND |
17 |
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18 |
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19 |
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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 |
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AGND |
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28 |
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AGND |
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29 |
AGND |
AGND |
AGND |
30 |
-12V |
AGND |
+12V |
31 |
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32 |
AVDD |
AVDD |
AVDD |
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Note : The unused pins of the 96-way connector are not shown.
– 4 – |
REV. 0 |
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