ANALOG DEVICES EVAL-AD7492CB Service Manual

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Evaluation Board for 12-bit high speed,

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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

INTRODUCTION

low power, successive-approximation ADC

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.

FUNCTIONAL BLOCK DIAGRAM

EVAL-AD7492CB

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-CON­TROL BRD2, all supplies are provided from the EVAL­CONTROL BRD2 through the 96 way connector.

When using the board as a stand alone unit, external supplies
must be provided. This evaluation board has five power
supply inputs: V
be connected to the V
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 A
be connected to the V
pins on all three op-amps. The V
provide an external voltage for the output drivers on the
AD7492. If an external V
the D

input which should be tied to 0 V. The supplies are

GND

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

DD

, A

, VSS, V

GND

input to supply the AVDD and DV

DD

input to supply the negative supply

SS

is supplied, it is referenced to

DRIVE

and D

DRIVE

DRIVE

GND

input. -5 V must

GND

input can be used to

. +5 V must

DD

Unipolar

Ain

Buffer

Vin

Bipolar

Ain

Bias-up

buffer

External

Reference

Ref Out

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.

AD7492 ADC

Data Bus

Control Lines

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

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EVAL-AD7492CB

reference are also decoupled to A
decoupled to A
decoupled to A

with 10uF tantalum and 0.1µF multilayer ceramic capacitors. The AD7492 DVDD and VDRIVE pins are

GND

with 10uF tantalum capacitors and to D

GND

with a 10µF tantalum and a 0.1µF ceramic capacitor. The AD7492 AVDD supply pin is

GND

with 0.1µF multilayer ceramic capacitors.

GND

Extensive ground planes are used on this board to minimize the effect of high frequency noise interference. There are two
ground planes, A

Analog Input Section

GND

and D

. These are connected at one location close to the AD7492.

GND

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 bias­up buffer circuit before being applied to the VIN pin of the AD7492. The input impedence of the bias-up circuit is 50Ω which
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 50Ω filter 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 This link selects the source of the V

When this link is in position "A" V
When this link is in position "B" V

LK9 This link selects the source of the V

When this link is in position "A" V
When this link is in position "B" V

supply.

DD

must be supplied from an external source via J2.

DD

is supplied from the EVAL-CONTROL BRD2.

DD

supply.

SS

must be supplied from an external source via J2.

SS

is supplied from the EVAL-CONTROL BRD2.

SS

–2–

REV. A

EVAL-AD7492CB

Continued on next page

LK10 This link must be in position "A" if a bipolar AIN signal is being applied to the bipolar Vin socket, SK3.

This link must be in position "B" if a unipolar AIN signal is being applied to the unipolar Vin socket, SK1.
LK11 This link is used to connect in the impedence matching resistor, R5, for unipolar Vin.
LK12 This link is used to connect in the impedence matching resistor, R7, for bipolar Vin.

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. All
links are set for use with the EVAL-CONTROL BRD2.

Table I. Initial Link and Switch Positions

Link No. Position Function.

LK1 B Provides DC bias voltage to the analog bias-up circuit using AD780 external reference.

LK2 B The digital logic circuitry is powered from the EVAL-CONTROL BRD2.

LK3 B Part goes into partial sleep mode if low power operation selected.

LK4 A CONVST signal is provided by the EVAL-CONTROL BRD2 via J1.

LK5 A RD signal is provided by the EVAL-CONTROL BRD2 via J1.

LK6 A CS signal is provided by the EVAL-CONTROL BRD2 via J1.

LK7 A AD7492 VDRIVE pin is connected to the AD7492 DVDD pin.

LK8 B V

LK9 B V

LK10 A The AD7492 Vin pin is connected to the bipolar Vin.

LK11 Inserted Unipolar Vin impedence matching resistor is connected into circuit.

LK12 Inserted Bipolar Vin impedence matching resistor is connected into circuit.

is supplied by the EVAL-CONTROL BRD2 via J1.

DD

is supplied by the EVAL-CONTROL BRD2 via J1.

SS

REV. A

–3–

EVAL-AD7492CB

EVAL-CONTROL BRD2 INTERFACING

Interfacing to the EVAL-CONTROL BRD2 is via a 96-way
connector, J1. The pinout for the J1 connector is shown in
Figure 2 and its pin designations are given in Table II.

1

A
B
C

1

Figure 1. Pin Configuration for the 96-Way

32

32

Connector, J1

96-Way Connector Pin Description

D0-D11 Data Bit 0 to Data Bit 11. Three-state TTL

outputs. D11 is the MSB.

+5VD Digital +5 V supply. This can be used to provide

a separate +5 V supply for the digital logic if
required via LK2.

RD Read. This is an active low logic input connected

to the RD pin of the AD7492 via LK5.

CS Chip Select. This is an active low logic input

connected to the CS pin of the AD7492 via LK6.

FL0 Flag zero. This logic input is connected to the

CONVST input of the AD7492 via LK4.

IRQ2 Interrupt Request 2. This is a logic output and is

connected to the BUSY logic output on the
AD7492.

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

SS

Negative Supply Voltage. This provides a nega-

tive supply to the on-board op-amps via LK9.

AV

DD

Positive Supply Voltage. This provides a positive
supply to the op-amps, the reference, the AD7492
and the digital logic.

When interfacing directly to the EVAL-CONTROL BRD2,
all power supplies and control signals are generated by the
EVAL-CONTROL BRD2. However, due to the nature of
the DSP interface on the EVAL-CONTROL BRD2, AD7492
sampling rates greater than 750 KHz are not supported when
interfacing the EVAL-AD7492CB directly to the EVAL­CONTROL BRD2.

Table II. 96-Way Connector Pin Functions.

ROW A ROWB ROWC

1
2D0
3D1
4 DGND DGND DGND
5D2
6D3
7D4
8 +5VD +5VD +5VD
9 RD D5
10 D6 CS
11 D7
12 DGND DGND DGND
13 D8
14 D9
15 D10
16 DGND DGND DGND
17 FL0 D11 IRQ2
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 AGND
31 AVSS AVSS AVSS
32 AVDD AVDD AVDD

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

–4–

REV. A

EVAL-AD7492CB

SOCKETS

There are three input sockets relevant to the operation of the
AD7492 on this evaluation board. The function of these
sockets is outlined in Table III.

Table III. Socket Functions

Socket Function

SK1 Sub-Miniature BNC Socket for unipolar ana-

log input. Analog inputs in the acceptable
AD7492 analog input range (0 V to REFIN)
are applied to this socket. The signal is then
buffered before it is applied to the AD7492
VIN pin.

SK2 Sub-Miniature BNC Socket for external

CONVST input.

SK3 Sub-Miniature BNC Socket for Bipolar ana-

log input The AD7492 can only accept analog
inputs in the range 0 V to REFIN. Bipolar
analog inputs in the range -1.25 V to +1.25 V
applied to this socket are biased up to the
acceptable AD7492 input range by the on­board bias-up circuit before being applied to
the AD7492 VIN pin.

CONNECTORS

There are three connectors on the AD7492 evaluation board
as outlined in Table IV.

Table IV. Connector Functions

OPERATING WITH THE EVAL-CONTROL BRD2

The evaluation board can be operated in a stand-alone mode
or operated in conjunction with the EVAL-CONTROL
BRD2. This EVAL-CONTROL BRD2 is available from
Analog Devices under the order entry "EVAL-CONTROL
BRD2". When interfacing directly to this control board, all
supplies and control signals to operate the AD7492 are
provided by the EVAL-CONTROL BRD2 when it is run
under control of the AD7492 software which is provided with
the AD7492 evaluation board package. This EVAL-CON­TROL BRD2 will also operate with all Analog Devices
evaluation boards which end with the letters CB in their title.

The 96-way connector on the EVAL-AD7492CB plugs
directly into the 96-way connector on the EVAL-CON­TROL BRD2. No power supplies are required in the system.
The EVAL-CONTROL BRD2 generates all the required
supplies for itself and the EVAL-AD7492CB. The EVAL­CONTROL BRD2 is powered from a 12 V AC transformer.
Suitable transformers are available as an accessory from
Analog Devices under the following part numbers:

EVAL-110VAC-US: For use in the U.S. or Japan
EVAL-220VAC-UK: For use in the U.K.
EVAL-220VAC-EU: For use in Europe
These transformers are also available for other suppliers

including Digikey (U.S.) and Campbell Collins (U.K.).
Connection between the EVAL-CONTROL BRD2 and the

serial port of a PC is via a standard RS-232 cable which is
provided as part the EVAL-CONTROL BRD2 package.
Please refer to the manual which accompanies the EVAL­CONTROL BRD2 for more details on the EVAL-CON­TROL BRD2 package.

Connector Function

J1 96-Way Connector for EVAL-CONTROL

BRD2 interface connections.

J2 External VDD, VSS & AGND power connec-

tor.

J3 External VDRIVE & DGND power connec-

tor.

REV. A

–5–