ANALOG DEVICES UG-258 Service Manual

Evaluation Board User Guide

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

UG-258

Evaluation Board for the AD5235 Digital Potentiometer

FEATURES

Full featured evaluation board for the AD5235
Several test circuits
Various ac/dc input signals
PC control via a separately purchased system demonstration

platform (SDP)
PC control software
26 extra bytes in EEMEM for user-defined information
Resistor tolerance error stored in EEMEM

PACKAGE CONTENTS

EVAL-AD5235SDZ evaluation board
CD that includes

Self-installing software that allows users to control the

board and exercise all functions of the device
Electronic version of the AD5235 data sheet
Electronic version of the UG-258 document

GENERAL DESCRIPTION

This user guide describes the evaluation board for evaluating the

AD5235—a dual-channel, 1024-position, nonvolatile memory

digital potentiometer. With versatile programmability, the AD5235
allows multiple modes of operation, including read/write access
in the RDAC and EEMEM registers, increment/decrement of
resistance, resistance changes in ±6 dB scales, wiper setting read­back, and extra EEMEM for storing user-defined information,
such as memory data for other components or a lookup table.

The AD5235 supports dual-supply ±2.25 V to ±2.75 V operation
and single-supply 2.7 V to 5.5 V operation, making the device
suited for battery-powered applications and many other appli­cations. In addition, the AD5235 uses a versatile SPI-compatible
serial interface, allowing speeds of up to 50 MHz .

The EVAL-AD5235SDZ can operate in single-supply and dual­supply mode and incorporates an internal power supply from
the USB.

Complete specifications for the AD5235 part can be found in
the AD5235 data sheet, which is available from Analog Devices,
Inc., and should be consulted in conjunction with this user
guide when using the evaluation board.

DIGITAL PICTURE OF EVALUATION BOARD WITH SYSTEM DEMONSTRATION PLATFORM

SYSTEM DEMONSTRATION

PLEASE SEE THE LAST PAGE FOR AN IMPORTANT
WARNING AND LEGAL TERMS AND CONDITIONS.

PLATFORM

EVAL-AD5235S DZ

Figure 1.

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UG-258 Evaluation Board User Guide

TABLE OF CONTENTS

Features.............................................................................................. 1

Package Contents.............................................................................. 1

General Description ......................................................................... 1

Digital Picture of Evaluation Board with System

Demonstration Platform.................................................................. 1

Revision History ............................................................................... 2

Evaluation Board Hardware............................................................ 3

Power Supplies ..............................................................................3

Link Options ................................................................................. 3

REVISION HISTORY

3/11—Revision 0: Initial Version



Test Circuits ...................................................................................4

Evaluation Board Software...............................................................6

Installing the Software..................................................................6

Running the Software ...................................................................6

Software Operation.......................................................................7

Evaluation Board Schematics and Artwork...................................8

Ordering Information.................................................................... 14

Bill of Materials........................................................................... 14

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Evaluation Board User Guide UG-258

EVALUATION BOARD HARDWARE

POWER SUPPLIES

The EVAL-AD5235SDZ supports the use of single and dual
power supplies.

In single-supply mode, the evaluation board can be powered
either from the SDP port or externally by the J1-1, J1-2, and
J1-3 connectors, as described in Ta bl e 1.

If dual-supply mode is required, the J1-1, J1-2, and J1-3 connectors
must provide the external power supply, as described in Tab le 1.

All supplies are decoupled to ground using 10 μF tantalum and

0.1 μF ceramic capacitors.

Table 1. Maximum and Minimum Voltages of the Connectors

Connector No. Label Voltage

J1-1 EXT VDD Analog positive power supply, VDD.

J1-2 GND Analog GND.
J1-3 EXT VSS Analog negative power supply, VSS.
For single-supply operation, it is 0 V.

For single-supply operation, it is

2.7 V to 5.5 V.
For dual-supply operation, it is

2.5 V to 2.75 V.

For dual-supply operation, it is

−2.5 V to −2.75 V.

LINK OPTIONS

Several link and switch options are incorporated into the evalu­ation board and should be set up before using the board. Tabl e 2
describes the positions of the links to control the evaluation board
by a PC, via the SDP board, using the EVAL-AD5235SDZ in
single-supply mode. The functions of these link and switch
options are described in detail in Tab l e 3 through Table 6.

Table 2. Link Options Setup for SDP Control (Default)

Link No. Option
A25 3.3 V
A24 GND

Table 3. Link Functions

Link No. Power Supply Options

A25 VDD This link selects one of the following as the positive power supply:
5 V (from SDP).

3.3 V (from SDP).
EXT VDD (external supply from the J1-1 connector).
A24 VSS This link selects one of the following as the negative power supply:
GND (analog ground).
VDD VSS (external supply from the J1-3 connector).

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UG-258 Evaluation Board User Guide

A

V

V

TEST CIRCUITS

The EVAL-AD5235SDZ incorporates several test circuits to
evaluate the AD5235 performance.

DAC

RDAC1 can be operated as a digital-to-analog converter (DAC),
as shown in Figure 2.

AC + DC

– V

V

DD

SS

2

– V

V

DD

2

Tabl e 4 shows the options available for the voltage references.

Table 4. DAC Voltage References

Terminal Link Options Description

A1 A20 AC + DC

VDD Connects Terminal A1 to VDD
W1 BUF-W1

B1 A21 DC

VSS Connects Terminal B1 to VSS
GND

The output voltage is defined in Equation 1.

OUT

where:

RDAC1 is the code loaded in the RDAC1 register.
V

is the voltage applied to the A1 terminal (A20 link).

A1

V

is the voltage applied to the B1 terminal (A21 link).

B1

Using the R34 and R35 external resistors, you can reduce the
voltage of the voltage references. In this case, use the A1 and
B1 test points to measure the voltage applied to the A1 and B1
terminals and recalculate V

AC Signal Attenuation

RDAC1 can be used to attenuate an ac signal, which must be
provided externally using the AC_INPUT connector, as shown
in Figure 3.

VDD

V

DD

RDAC1

DC

SS

VSS

V

SS

GND

A1

R34

W1

R35

W1

B1

BUF-W1

W1_BUF

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A1

B1

Figure 2. DAC

Connects Terminal A1 to

− VSS)/2

(V

DD

Connects Terminal W1 to an
output buffer

Connects Terminal B1 to

− VSS)/2

(V

DD

Connects Terminal B1 to
analog ground

RDAC1

×−=

)(

VVV

1

B

1

A

(1)

1024

and VB1 in Equation 1.

A1

–

DD

SS

2

C_INPUT

1µF

V

DD

– V

2

AC + DC

AC

A1

R34

RDAC1

A1

B1

DC

SS

VSS

V

SS

GND

W1

R35

W1

BUF-W1

R36

B1

W1_BUF

Figure 3. AC Signal Attenuator

Depending on the voltage supply rails and the dc offset voltage
of the ac signal, various configurations can be used, as described
in Tabl e 5 .

Table 5. AC Signal Attenuation Link Options

Maximum
Voltage
Supply

AC Signal

Amplitude

Link Options Conditions

Single VDD A20 AC + DC No dc offset voltage.

AC signal is outside
the voltage supply
rails due to the
dc offset voltage.

DC offset voltage

/21.

≠ V

DD

AC All other conditions.
A21 DC

Use in conjunction

with AC + DC link.
GND All other conditions.
Dual VDD/VSS A20 AC + DC

AC signal is outside

the voltage supply

rails due to the

dc offset voltage

DC offset voltage

1

.

≠ 0 V
AC All other conditions.
A21 GND

Use in conjunction

with AC + DC link.
VSS All other conditions.

1

Recommended to ensure optimal total harmonic distortion (THD) performance.

The signal attenuation is defined in Equation 2.

⎛
⎜

nAttenuatio log20)dB( (2)

×=

⎜

R

⎝

⎞

+

RR

WWB1

⎟
⎟

−− ENDTOEND

⎠

where:

R

is the resistor between the W1 and B1 terminals.

WB1

is the wiper resistance.

R

W

R

END-TO-END

is the end-to-end resistance value.

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Evaluation Board User Guide UG-258

V

In addition, R36 can be used to achieve a pseudologarithmic
attenuation. To do so, adjust the R36 resistor until a desirable
transfer function is found.

Signal Amplifier

RDAC2 can be operated as an inverting or noninverting signal
amplifier supporting linear or pseudologarithmic gains. Tab le 6
shows the available configurations.

Table 6. Amplifier Selection Link Options

Amplifier Gain Link Label

Noninverting Linear A27 LINEAR
A29 NONINVERTING

R43 and R42 can be used to set the maximum and minimum
gain limits.

The inverting amplifier with linear gain is shown in Figure 6,
and the gain is defined in Equation 5.

A30 NONINVERTING
Pseudologarithmic A27 PSEUDOLOG
A29 NONINVERTING
A30 NONINVERTING

where R

Inverting Linear A27 LINEAR
A29 INVERTING
A30 INVERTING
Pseudologarithmic A27 PSEUDOLOG
A29 INVERTING
A30 INVERTING

The noninverting amplifier with linear gain is shown in Figure 4,
and the gain is defined in Equation 3.

R

WB2

G

where R

1+=

WB2

(3)

R38

is the resistor between the W2 and B2 terminals.

R41

R38

2.7kΩ

W2

W2

1.7kΩ

RDAC2

10nF

B2

R42

B2

V

IN

Figure 4. Linear Noninverting Amplifier

V

OUT

OAVOUTC1

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The inverting amplifier with pseudologarithmic gain is shown
in Figure 7, and the gain is defined in Equation 6.

where:

R

WB2

R

AW 2

The noninverting amplifier with pseudologarithmic gain is
shown in Figure 5, and the gain is defined in Equation 4.

R

2

WB

1

G += (4)

R

2

AW

where:

R

is the resistor between the W2 and B2 terminals.

WB2

R

is the resistor between the A2 and W2 terminals.

AW 2

R43 and R42 can be used to set the maximum and minimum
gain limits.

R41

R43

1.7kΩ

IN

W2

A2

W2

RDAC2

10nF

B2

B2A2

C1

R42

V

OUT

OAVOUT

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V

Figure 5. Pseudologarithmic Noninverting Amplifier

R

WB2

G

−=

WB2

(5)

R38

is the resistor between the W2 and B2 terminals.

R41

1.7kΩ

R38

2.7kΩ

V

IN

W2

W2

RDAC2

10nF

B2

B2

C1

R42

V

OUT

OAVOUT

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Figure 6. Linear Inverting Amplifier

R

G −=

WB

(6)

R

22AW

is the resistor between the W2 and B2 terminals.
is the resistor between the A2 and W2 terminals.

R41

1.7kΩ

V

OUT

C1

W2

W2

A2

R43

IN

RDAC2

B2

B2A2

Figure 7. Pseudologarithmic Inverting Amplifier

10nF

R42

OAVOUT

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