Analog Devices DC2904A-B User manual

User Guide | DC2904A
UG-2018
Evaluating the LTC2686 8-Channel, 16-Bit Voltage Output SoftSpan DAC
PLEASE SEE THE LAST PAGE FOR AN IMPORTANT
WARNING AND LEGAL TERMS AND CONDITIONS. Rev. 0 | 1 of 11
FEATURES
►Fully featured evaluation board for the LTC2686 multichannel
voltage output DAC
►Flexible output power supply configuration
►Easy connection to external loads
►Test points to monitor DAC status signals
►ACE evaluation software compatible
EVALUATION KIT CONTENTS
►DC2904A-B evaluation board
►Ribbon cable to connect to the Linduino DC2026C controller
board
EQUIPMENT NEEDED
►DC2026C controller board (must be purchased separately)
►PC running Windows® 7 or Windows 10
►Voltmeter
►Power supply
SOFTWARE NEEDED
►ACE evaluation software (available for download from the
DC2904A product page)
DOCUMENTS NEEDED
►LTC2686 data sheet
►DC2904A-B design files (see the DC2904A product page)
GENERAL DESCRIPTION
The DC2904A-B is a fully featured evaluation board that is used
to evaluate the LTC2686, an 8-channel, precision voltage output
digital-to-analog converter (DAC).
The DC2904A-B is controlled through a serial peripheral interface
(SPI) from the J1 connector. The SPI signals are sent from the
DC2026C controller board through the ribbon cable that is connect-
ed to the DC2904A-B.
The DC2904A-B uses Analysis, Control, Evaluation (ACE) software
to provide an intuitive graphical user interface (GUI) that configures
and controls the LTC2686 using the SPI interface.
The LTC2686 is used for various voltage mode biasing applications
such as optical modulators for data communications. The output
voltage range for each channel is software selectable, and any
channel can be routed to the DC2904A-B MUX pin, allowing either
the channel voltage or current to be externally monitored.
For full specifications on the LTC2686, see the LTC2686 data
sheet, which must be consulted in conjunction with this user guide
when using the DC2904A-B.
EVALUATION BOARD PHOTOGRAPH
Figure 1. DC2904A-B Evaluation Board

User Guide DC2904A
TABLE OF CONTENTS
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Features................................................................ 1
Evaluation Kit Contents......................................... 1
Equipment Needed................................................1
Software Needed...................................................1
Documents Needed...............................................1
General Description...............................................1
Evaluation Board Photograph................................1
Evaluation Board Hardware...................................3
Evaluation Board Overview................................3
Power Supplies.................................................. 3
Analog Outputs...................................................4
Digital Interface.................................................. 4
Reference...........................................................4
Multiplexer Output.............................................. 4
On-Board Connectors........................................ 4
Getting Started...................................................... 5
Software Installation Procedures........................5
Evaluation Hardware Setup................................5
Software Operation............................................ 5
Main Window......................................................6
Troubleshooting...................................................10
Hardware..........................................................10
Ordering Information............................................11
REVISION HISTORY
10/2021—Revision 0: Initial Version

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EVALUATION BOARD HARDWARE
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EVALUATION BOARD OVERVIEW
The DC2904A-B requires the power connections and connection
to the DC2026C controller board shown in Figure 2. The ribbon
cable provided in the evaluation kit connects the DC2904A-B and
the DC2026C via the J1 connector. Turrets are provided to connect
the DC2904A-B to the power supplies.
The DC2904A-B has other optional features to allow the user to
select an external reference, provide separate supply voltages for
Channel 0 to Channel 3 and Channel 4 to Channel 7, and to
monitor various outputs through the on-board MUX pin. These
optional features do not need to be changed for normal operation.
POWER SUPPLIES
The DC2904A-B is powered using external supplies. The minimum
requirement to power the DC2904A-B is to provide 5.0 V to 21 V on
E2 (V1+) and connect E3 (GND) and E4 (V−) to ground (GND).
As an alternative, the supply connection to E4 (V−) can be in
the range between −21 V and ground (GND) to accommodate
applications that require a negative supply.
The default position for JP5 (V1+ = V2+) is in the CONNECT
position. This position connects the V1+ and V2+ power supplies so
that they are at the same voltage. By changing JP5 to the NC (not
connected) position, V1+ and V2+ are decoupled on the evaluation
board and can be driven with separate supplies. V1+ and V2+ have
the same requirement. They must be in the range of 5 V to 21 V but
do not need to be the same voltage when decoupled. However, V2+
must be less than or equal to V1+.
E10 (VCC) and E5 (IOVCC) are supplied from on-board regulators
by default. If desired, these voltages can be driven with an external
supply.
Figure 2. DC2904A-B Hardware Connections

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ANALOG OUTPUTS
The analog outputs, VOUT0 to VOUT7, are available on the E13, E14,
E15, E16, E17, E18, E19, and E20 turrets, respectively. Return
paths for the ground currents are available on the E3 and E23
(GND) turrets. These turrets must be connected to load GND.
DIGITAL INTERFACE
DC2026C Connections
The DC2904A-B uses the DC2026C to communicate with the ACE
evaluation software through the USB port on the DC2026C. Use
the provided ribbon cable to connect J1 of the DC2904A-B to J1
of the DC2026C. When this connection is made, the DC2026C
powers the electrically erasable programmable read only memory
(EEPROM) on the DC2904A-B. The ACE evaluation software uses
the EEPROM to identify the DC2904A-B and load the proper plugin.
To ensure proper serial transfers and compatibility, the DC2026C
powers the IOVCC pin of the LTC2686, which is nominally 5 V.
DC2026C Connector Pin Descriptions
Figure 3 shows the pins for the DC2026C J1 connector. For de-
scriptions of each pin, see Table 1.
Figure 3. DC2026C J1 Connector Pins
Table 1. DC2026C Connector J1 Pin Descriptions
Pin No. Mnemonic Description
1 V+ Unregulated voltage from the DC2026C,
nominally 7 V
2 VCCIO I/O voltage set by JP3 on the DC2026C
3 GND Ground
4 SCL/SCK Serial clock from the DC2026C
5 MISO Serial data from the DC2904A-B
6 CS Chip select from the DC2026C
7 SDA/MOSI Serial data from the DC2026C
8 GND Ground
9 EEDA Serial data for EEPROM
10 EEVCC Power supply (VCC) for EEPROM
11 EESCL Serial clock for EEPROM
12 EEGND Ground for EEPROM
13 GND Ground
14 NC No connection
REFERENCE
By default, the DC2904A-B uses the internal reference of the
LTC2686. To use an external reference, place the DC2904A-B JP1
(REF SEL) jumper into the EXT position and apply an external
reference to E11 (REF).
MULTIPLEXER OUTPUT
The LTC2686 has an internal multiplexer that allows monitoring of
compliance voltages, output currents, and internal die temperature.
The output compliance voltages and representative voltages of
the output current and internal die temperature are available on
the LTC2686 MUX pin and can be routed to the DC2904A-B E21
connector (MUX) using the LTC2686-16 Memory Map view in the
ACE GUI (see Figure 8), and setting the appropriate bits in the
analog mux control register. Refer to the LTC2686 data sheet for
more details on the multiplexer functionality and register structure.
ON-BOARD CONNECTORS
Table 2 describes the on-board connectors on the DC2904A-B.
Table 2. On-Board Connectors
Connector Function
J1 SPI/I2C interface pin header connector
JP1 Internal or external reference select
JP2 Toggle Pin 0 (TGP0)
JP3 Toggle Pin 1 (TGP1)
JP4 Toggle Pin 2 (TGP2)
JP5 Connect or disconnect V1+ and V2+
E1 V2+
E2 V1+
E3, E6, E7, E12, E23 GND
E4 V−
E5 IOVCC
E8 CLR
E9 LDAC
E10 VCC
E11 REF
E13 Channel 0 voltage output (VOUT0)
E14 Channel 1 voltage output (VOUT1)
E15 Channel 2 voltage output (VOUT2)
E16 Channel 3 voltage output (VOUT3)
E17 Channel 4 voltage output (VOUT4)
E18 Channel 5 voltage output (VOUT5)
E19 Channel 6 voltage output (VOUT6)
E20 Channel 7 voltage output (VOUT7)
E21 MUX
E22 FAULT

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GETTING STARTED
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The ACE evaluation software controls and configures the on-board
LTC2686 through the DC2026C.
SOFTWARE INSTALLATION PROCEDURES
Before connecting the DC2026C to the DC2904A-B, follow these
steps to set up the DC2904A-B for initial use in the ACE evaluation
software:
1. Download the ACE evaluation software package from the
DC2904A-B product page at www.analog.com/DC2904A to
start the ACE evaluation software installation.
2. Open the ACEInstall_1.21.xxxx.xxxx.exe file and follow the
instructions in the folder to complete the software installation
process.
EVALUATION HARDWARE SETUP
When the ACE evaluation software installation is complete, follow
these steps to set up the DC2026C and the DC2904A-B together:
1. Connect the DC2026C to the DC2904A-B via the J1 connectors
with the ribbon cable provided (see Figure 2).
2. Connect the desired power supplies to E2 (V1+), E3 (GND),
and E4 (V−) on the DC2904A-B.
3. Connect the desired load to the appropriate channel on the
DC2904A-B.
4. Connect the load ground to a ground (GND) turrets (either E3
or E23) on the DC2904A-B.
5. Connect the DC2026C to a PC or laptop using the USB cable.
6. Start the ACE evaluation software (see the Software Operation
section).
SOFTWARE OPERATION
To start the ACE evaluation software, from the Start menu, click
Analog Devices > ACE. The software window opens (see Figure
4) until the software recognizes the DC2904A-B. When the software
recognizes the DC2904A-B, the main software window in Figure 5
opens.
Figure 4. Interface Window

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Figure 5. ACE Evaluation Software Main Window
MAIN WINDOW
In the main ACE evaluation software window (see Figure 5), each
channel can be controlled. Various settings for the LTC2686 are
available in this window, allowing the user to configure the output
range, output voltage, gain adjustment, offset adjustment, toggle
options, and dither options of each channel.
Refer to the LTC2686 data sheet for more information on the
device features associated with the different tab functions that are
described in the following sections.
Reference Configuration
The DC2904A-B uses the LTC2686 internal reference to set the
full-scale range. To apply an external reference, click the box
labeled Reference Select (see Figure 5).
Setting the Channel Output Range
To set the output range for a specific channel on the LTC2686,
1. Select the channel from the Channel Select dropdown box.
2. Select the desired range for the selected channel using the
Span selection dropdown box (see Figure 5).
Setting the Channel Voltage Value
To set the output voltage for a specific channel on the LTC2686,
1. Select the channel from the Channel Select dropdown box.
2. Type the desired value into the Register A text box (see
Figure 5).
Toggling Between A and B Output Registers
Each channel has two output registers that can be written inde-
pendently.
1. Click the Register A or Register B option to select the register
to write to.
2. Type the desired hexadecimal value into the Register A (or
Register B) text box (see Figure 5).
Settling Offset and Gain Values
Each channel can have an offset and gain value applied to the
output. The value is applied to each channel independently.
1. Select the channel from the Channel Select dropdown box.
2. Type the desired hexadecimal offset or gain adjust value into
the Offset Adjust or Gain Adjust text boxes (see Figure 5).
Enabling Toggle Mode
Toggle mode can be enabled by selecting the Enable Toggle/Dith-
er Functionality check box (see Figure 5). This check box enables
the toggle view shown in Figure 6. The toggle signal can then be
applied to the selected pin or supplied internally.

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Enabling Dither Mode
After enabling the toggle view shown in Figure 6 as described in
the Enabling Toggle Mode section, select the dither mode from the
Mode dropdown box to bring up the dither options (see Figure 7).
The default values for the dither phase (ⱷ0) and period (N) are 0°
and N = 4. The phase and period of the dither can be modified
using the dropdown boxes to select from a fixed list of options.
Figure 6. Toggle View

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Figure 7. Dither View

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Memory Map View
To access the LTC2686-16 Memory Map view, click the Proceed
to Memory Map button from the software main window
(see Figure 5).
Figure 8. LTC2686-16 Memory Map View

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TROUBLESHOOTING
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HARDWARE
A comprehensive list of frequently asked questions (FAQ) is availa-
ble on the LTC2686 FAQs page in the EngineerZone™ site. For
other questions, submit them to the Precision DACs section of the
EngineerZone site.