ANALOG DEVICES EVAL-AD7898CB Service Manual

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a

Evaluation Board for 5V , 12-Bit, Serial

220kSPS ADC in 8-Pin Package

EVAL-AD7898CB

FEATURES
Full-Featured Evaluation Board for the AD7898

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 AD7898 which is a fast 12-bit ADC that operates from a
single +5 V supply and is housed in an 8-pin SOIC. Full data
on the AD7898 is available in the AD7898 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 CS/CONVST input, VDRIVE input, SDATA input,
SCLK input, REFIN input and the VIN input.

FUNCTIONAL BLOCK DIAGRAM

OPERATING THE AD7898 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 seven
power supply inputs: V
V

. If the evaluation board is used in stand-alone

DRIVE

mode +5V must be connected to the V
the AD7898 V

pin and the AD780 voltage reference.

DD

DD

, A

, +12V, -12V, A

GND

GND

input to supply

DD

, and

+12V and -12V are used to supply the op-amps. The
V

pin can be driven by a voltage between +3V and

DRIVE

+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

0.1µF ceramic capacitor. The AD7898 AV
decoupled to A

with 10 µF tantalum and 0.1µF multi-

GND

with 10µF tantalum and a

GND

supply pin is

DD

layer 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

. These are con-

GND

nected at one location close to the AD7898.

ANALOG

INPUT

ad7898

EXTERNAL

REFERENCE

Vdrive

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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.

Vdd

CS

SDATA

SCLK

Vdd

One Technology Way, P.O. Box 9106, Norwood. MA 02062-9106, U.S.A.
Tel: [phone] Fax: [phone]

EV AL-AD7898CB

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 below.

Link No. Function.

LK1 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.

LK2 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 VIN 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.

LK3 This link is used to select the source of the reference voltage applied to the AD7898 REFIN pin.

When this link is in position "A", the AD780 provides the 2.5V reference to the AD7898.
When this link is in position "B" an external reference must be supplied via J5.

LK4 This link selects the source of the V

When this link is in position "A" the +5V is supplied from the EVALUATION-BOARD CONTROLLER.
When this link is in position "B" the +5V must be supplied from an external source via J2.

LK5 This link option selects the source of the CS/CONVST input.

When this link is in position "A" the CS/CONVST input is provided by the EVALUATION-BOARD
CONTROLLER.
When this link is in position "B" the CS/CONVST input is provided via the external socket, J6.

LK6 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" an external VDRIVE supply voltage must be supplied via J7.

LK7 This link link option selects the source of the SCLK input.

When this link is in position "A" the SCLK input is provided by the EVALUATION-BOARD CONTROL­LER.
When this link is in position "B" the SCLK input is provided via the external socket, J9.

LK8 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, J3.

LK9 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, J3.

LK10 LK11 These two link options are used to add an invertor to the SCLK path.

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. "B" is the normal position for these 2 link
options.

+5V supply.

DD

–2–

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EV AL-AD7898CB

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 Removed 50Ω termination is not selected.

LK2 A Vin Jack, J4 is tied to the input of the AD711 buffer op-amp.

LK3 A The on-board AD780 voltage reference supplies the REFIN pin of the AD7898.

LK4 A V

LK5 A CS/CONVST is supplied from the EVALUATION-BOARD CONTROLLER via

LK6 A VDRIVE pin of the AD7898 is connected to V

LK7 A SCLK input is supplied from the EVALUATION-BOARD CONTROLLER via

LK8 A +12V supplied from EVALUATION-BOARD CONTROLLER via J1.

LK9 A -12V supplied from EVALUATION-BOARD CONTROLLER via J1.

LK10 LK11 B & B SCLK generated by the EVALUATION-BOARD CONTROLLER is not in-

(+5V) supplied by the EVALUATION-BOARD CONTROLLER via J1.

DD

J1.

(+5V)

DD

J1.

verted.

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–3–

EV AL-AD7898CB

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
EVALUATION-BOARD CONTROLLER or other sys­tems. The pinout for the J1 connector is shown in Figure
1 and its pin designations are given in Table II.

It is important to note that the evaluation board is set-up
for Mode 1 operation only. This means that the
CONVST/CS will always be CS ( see AD7898 datasheet -
modes of operation section).

1

A
B
C

1

Figure 1. Pin Configuration for the 96-Way
Connector, J1

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

supply line on the board via LK4.

DD

+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.

32

32

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

–4–

Note : The unused pins of the 96-way connector are not shown.

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