ANALOG DEVICES UG-391 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-391

Evaluation Board for the AD5258 Digital Potentiometer

FEATURES

Full-featured in conjunction with low voltage digiPOT

motherboard (EVAL-MB-LV-SDZ)
Various test circuits
Various ac/dc input signals
PC control via a separately purchased system demonstration

platform (SDP-B or SDP-S)
PC software for control

PACKAGE CONTENTS

EVAL-AD5258DBZ board

EVAL-MB-LV-SDZ motherboard
CD that includes

Self-installing software that allows users to control the

board and exercise all functions of the device
Electronic version of the AD5258 data sheet
Electronic version of the UG-391 user guide

GENERAL DESCRIPTION

This user guide describes the evaluation board for evaluating the

AD5258, a single-channel, 64-position, nonvolatile memory

digital potentiometer in conjunction with the low voltage digiPOT
motherboard.

The AD5258 supports single-supply 2.7 V to 5.5 V operation,
making the device suited for battery-powered applications and
many other applications with superior low temperature
coefficient performance.

In addition, the AD5258 uses a versatile I
operates in fast mode, allowing speeds of up to 400 kHz. This
interface can be used to read back the wiper register and
EEPROM content.

The EVAL-MB-LV-SDZ can operate in single-supply mode and
incorporates an internal power supply from the USB.

Complete specifications for the AD5258 part can be found in
the AD5258 data sheet, which is available from Analog Devices,
Inc., and should be consulted in conjunction with this user
guide when using the evaluation board.

2

C serial interface that

EVAL-AD5258DBZ WITH MOTHERBOARD AND SDP-B

Figure 1. Digital Picture of Evaluation Board with Low Voltage DigiPOT Motherboard and System Demonstration Platform

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

10619-001

Rev. 0 | Page 1 of 16

UG-391 Evaluation Board User Guide

TABLE OF CONTENTS

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

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

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

EVAL-AD5258DBZ with Motherboard and SDP-B .................... 1

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

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

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

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

Signal Amplifier ............................................................................ 5

REVISION HISTORY

5/12—Revision 0: Initial Version

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

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

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

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

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

Motherboard ..................................................................................8

Daughter Board .......................................................................... 12

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

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

Rev. 0 | Page 2 of 16

Evaluation Board User Guide UG-391

EVALUATION BOARD HARDWARE

POWER SUPPLIES

The EVAL-MB-LV-SDZ supports using single power supplies.

The evaluation board can be powered either from the SDP port
or externally by the J1 and J2 connectors, as described in Table 1.

All supplies are decoupled to ground using 10 μF tantalum and

0.1 μF ceramic capacitors.

Link Options

Several link and switch options are incorporated in the EVAL­MB-LV-SDZ board and should be set up before using the board.
Table 2 describes the positions of the links to control the
evaluation board by a PC, via the SDP board. The functions of
these link options are described in detail in Table 3 through
Tabl e 6.

Table 1. Maximum and Minimum Voltages of the Connectors

Connector
No. Label Voltage

J1-1 EXT VDD Analog positive power supply, VDD,
from 2.7 V to 5.5 V
J1-2 GND Analog ground
J2-1 VLOGIC Digital supply, from 2.7 V to VDD
J2-2 DGND Digital ground

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

Link No. Option
A11 3.3 V
A12 AGND
A5 3.3 V

Table 3. Link Functions

Link No. Power Supply Options

A11 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 connector).
A5 V

A12 GND AGND.

This link selects one of the following as the digital supply:

LOGI C

3.3 V (from SDP).
VLOGIC (external supply from the J2 connector).

Rev. 0 | Page 3 of 16

UG-391 Evaluation Board User Guide

V

V

V

V

TEST CIRCUITS

The EVAL-AD5258DBZ and EVAL-MB-LV-SDZ incorporate
several test circuits to evaluate the performance of the AD5258.

DAC

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

–

2

– V

2

AC+

SS

VDD

V

DD

SS

RDAC

BIAS

AGND

R34

A1

A

B

W

R35

W1

B1

BUF-W1

VOUT1

10619-002

Figure 2. DAC

RDAC

)(

VVV



B

A

(1)

64

and VB in Equation 1.

A

DD

V

DD

Table 5 shows the options available for the voltage references.

The output voltage is defined in Equation 1.

OUT

where:

RDAC is the code loaded in the RDAC register.
V

is the voltage applied to the A terminal (A9 link).

A

V

is the voltage applied to the B terminal (A10 link).

B

However, by using the R34 and R35 external resistors, the user
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
A and B terminals and recalculate V

AC Signal Attenuation

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

–

DD

1kHz

HPF

AC_INPUT

SS

2

AC+

AC

R34

A1

RDAC

A

B

V

– V

DD

BIAS

SS

2

AGND

W

R35

W1

B1

VOUT1

BUF-W1

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 Table 4.

Table 4. AC Signal Attenuation Link Options

Link Options Conditions

A9 AC+ No dc offset voltage.

AC signal is outside the voltage supply rails

due to the dc offset voltage.
DC offset voltage ≠ VDD/21.
AC All other conditions.
A10 BIAS Use in conjunction with AC+ link1.
AGND 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



WWB




 ENDTOEND



where:

R

is the resistor between the W and B terminals.

WB

is the wiper resistance.

R

W

R

END-TO-END

is the end-to-end resistance value.

10619-003

Table 5. DAC Voltage References

Terminal Link (Daughter Board) Link (Motherboard) Options Description

A1 Switch B of A4 A9 AC+ Connects Terminal A1 to VDD /2
VDD Connects Terminal A1 to VDD
W1 Switch B of A3 BUF-W1 Connects Terminal W1 to an output buffer
B1 Switch B of A2 A10 BIAS Connects Terminal B1 to VDD/2
AGND Connects Terminal B1 to analog ground
A1 inserted Closes feedback loop of second op amp in the AD8618

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Evaluation Board User Guide UG-391

SIGNAL AMPLIFIER

The RDAC can be operated as an inverting or noninverting
signal amplifier supporting linear or pseudologarithmic gains.
Table 6 shows the available configurations.

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

R

WB

G

where R

WB

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

G  1 (4)

where:

is the resistor between the W and B terminals.

R

WB

R

is the resistor between the A and W terminals.

AW

(3)

1

R38

is the resistor between the W and B terminals.

R41

W2

1.7kΩ

R38

2.7kΩ

WB

RDAC

10nF

B2

C1

VOUT2

R42

Figure 4. Linear Noninverting Amplifier

10619-004

V

IN

R

WB

R

AW

R41

1.7kΩ

V

R43

IN

W2

A2

AB

RDAC

C1

10nF

B2

W

R42

VOUT2

10619-005

Figure 5. Pseudologarithmic Noninverting Amplifier

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.

Note that the input signal, V

R

WB

G

where R

WB

(5)



R38

is the resistor between the W and B terminals.

R38

2.7kΩ

V

IN

W2

RDAC

Figure 6. Linear Inverting Amplifier

, must be negative.

IN

R41

1.7kΩ

C1

10nF

WB

B2

R42

VOUT2

10619-006

Table 6. Amplifier Selection Link Options

Amplifier Gain Link (Daughter Board) Link (Motherboard) Label V

Range

IN

Noninverting Linear Switch A of A2, A3, and A4 A7 LIN 0 V to VDD
A6 N-INV
A1 not inserted A8 N-INV
Pseudologarithmic Switch A of A2, A3, and A4 A7 LOC 0 V to VDD
A6 N-INV
A1 not inserted A8 N-INV
Inverting Linear Switch A of A2, A3, and A4 A7 LIN −VDD to 0 V
A6 INV
A1 not inserted

A8 INV

Rev. 0 | Page 5 of 16