ANALOG DEVICES DC2903A Evaluation Board User Guide

ANALOG DEVICES DC2903A Evaluation Board User Guide

FEATURES

Fully featured evaluation board for the LTC2672 QuikEval evaluation software compatible Sample Arduino code compatible (available on the Linduino web page)

EVALUATION KIT CONTENTS

DC2903A evaluation board
Ribbon cable to connect to the Linduino DC2026C

EQUIPMENT NEEDED

DC2026C controller board (must be purchased separately)

PC running Windows® 7 or Windows 10
Current meter

SOFTWARE NEEDED

QuikEval evaluation software (available for download from the DC2903A product page)

DOCUMENTS NEEDED

LTC2672 data sheet
DC2903A design files (see the DC2903A product page)

GENERAL DESCRIPTION

The DC2903A is a fully featured evaluation board that evaluates the LTC2672, a five-channel, 16-bit, current source output digital-to-analog converter (DAC).

The DC2903A 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 connected to the DC2903A.

The DC2903A uses QuikEval evaluation software to provide an intuitive graphical user interface (GUI) that configures and controls the LTC2672 using the SPI interface.

The LTC2672 is used for various current mode biasing applications such as tunable lasers or resistive heaters. The output current ranges are software selectable, and each channel is routed to the DC2903A MUX pin for external monitoring.

For full specifications on the LTC2672, see the LTC2672 data sheet, which must be consulted in conjunction with this user guide when using the DC2903A.

EVALUATION BOARD PHOTOGRAPH

Figure 1. DC2903A Evaluation Board

EVALUATION BOARD HARDWARE

EVALUATION BOARD OVERVIEW

The DC2903A 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 DC2903A and the DC2026C via the J1 connector. Turrets are provided to connect the DC2903A to the power supplies.

The DC2903A has other optional features to allow the user to select an external reference, change the full-scale current, and monitor various outputs through the on-board monitor MUX pin. These optional features do not need to be changed for normal operation.

POWER SUPPLIES
The DC2903A is powered using external supplies. The minimum requirement to power the DC2903A is to provide 2.1 V to 5.5 V on E6 (VCC) and connect E7 (GND) and E8 (V−) to ground (GND). The supply connection to E8 (V−) can be from −5.5 V to ground (GND) to accommodate applications that require a negative supply.

E23 and E25 to E28 (VDD0 to VDD4, respectively) can be connected to a separate external supply to power the output stages of the individual device channels. To use an external supply on a channel, set the corresponding jumper, JP3 to JP7 (VDD0 to VDD4, respectively), to the EXT position and apply power to the appropriate turret (E23, E25, E26, E27, or E28).

Figure 2. DC2903A Hardware Connections

ANALOG OUTPUTS

The analog outputs, OUT0 to OUT4, are available on the E11, E9, E15, E17, and E19 turrets, respectively. Return paths for the ground currents are available on the E12, E14, E16, E18, and
E22 (GND) turrets. Because the corresponding LTC2672 analog outputs are currents, the load that is connected to the OUT0 to OUT4 outputs must have a return connection to ground (GND) via the appropriate GND turret.

DIGITAL INTERFACE
DC2026C Connections
The DC2903A uses the DC2026C to integrate with the QuikEval evaluation software through the SPI. Use the provided ribbon cable to connect J1 of the DC2903A to J1 of the DC2026C. When this connection is made, the DC2026C powers the electrically erasable programmable read-only memory (EEPROM) on the DC2903A. The QuikEval evaluation software uses the EEPROM to identify the DC2903 and load the proper module.

To ensure proper serial transfers and compatibility, the DC2026C powers the IOVCC pin of the LTC2672, which is nominally 5 V. DC2026C Connector Pin Descriptions Figure 3 shows the pins for the DC2026C J1 connector. For descriptions of each pin, see Table 1.

Table 1. DC2026C Connector J1 Pin Descriptions

REFERENCE
By default, the DC2903A uses the internal reference of the LTC2672. To use an external reference, place the DC2903A JP1 jumper into the EXT position and apply an external reference to E10 (REF).

MULTIPLEXER OUTPUT
The LTC2672 has a diagnostic feature that outputs compliance voltages, output currents, and internal die temperature monitoring. The output compliance voltages and representative voltages of the output current and internal die temperature are multiplexed on-chip and are available on the DC2903A E20 connector (MUX). Refer to the LTC2672 data sheet for more details on the multiplexer functionality.

PRECISON RSET RESISTOR
The LTC2672 integrates an on-chip, 20 kΩ resistor that defines the reference current generation. Additionally, the DC2903A contains an optional on-board location for a ±0.2 ppm/°C precision resistor. Refer to the LTC2672 data sheet for more details on the optional external precision resistor.

ON-BOARD CONNECTORS
Table 2 describes the 33 on-board connectors on the DC2903A.

Table 2. On-Board Connectors

GETTING STARTED

The QuikEval evaluation software controls and configures the on-board LTC2672 through the DC2026C. SOFTWARE INSTALLATION PROCEDURES

Before connecting the DC2026C to the DC2903A, take the following steps to set up the DC2903A for initial use in the QuikEval evaluation software:

1. Download the QuikEval evaluation software package from the DC2903A product page to start the QuikEval evaluation software installation.
2. Open the ltcqev.exe file and follow the instructions in the folder to complete the software installation process.

EVALUATION HARDWARE SETUP
When the QuikEval evaluation software installation is complete, take the following steps to set up the DC2026C and the DC2903A together:

1. Connect the DC2026C to the DC2903A via the J1 connectors with the ribbon cable provided (see Figure 2).
2. Connect the desired power supplies to E6 (VCC), E7 (GND), and E8 (V−) on the DC2903A.
3. Connect the desired load to the appropriate channel on the DC2903A E11 pin (OUT0), E9 pin (OUT1), E15 pin (OUT2), E17 pin (OUT3), or E19 pin (OUT4).
4. Connect the load to a ground (GND) pin on the DC2903A (E12, E14, E16, E18, or E22) to complete the ground return path.
5. Start the QuikEval evaluation software (see the Software Operation section).

Figure 5. QuikEval Evaluation Software Main Window

SOFTWARE OPERATION
To start the QuikEval evaluation software, from the Start menu, click Analog Devices > QuikEval. The software window opens (see Figure 4) until the software recognizes the DC2903A. When the software recognizes the DC2903A, the main software window in Figure 5 opens.

Figure 4. Select Interface Window

MAIN WINDOW
In the main QuikEval evaluation software window (see Figure 5), each channel can be written individually or all channels can be written at once as a group. Various settings for the LTC2672 are available in this window, including the range, reference voltage, toggle options, and full-scale adjustment resistor (R_FSADJ) settings. The fault register is read and displayed after every data transfer. Refer to the LTC2672 data sheet for more information on the device features associated with the different tab functions that are described in the following sections.

See the Using the Software section for more details on the controls displayed in the main QuikEval evaluation software window.

Reference Configuration
The DC2903A uses the LTC2672 internal 20 kΩ resistor to set the full-scale range. If a different resistor is manually populated on R4 of the DC2903A, the resistor value can be changed in the R_FSADJ (KΩ) text box (see Figure 5).

Similarly, if a different external reference voltage is used, the resistor value can be changed in the V_REF (V) text box (see Figure 5).

Setting the Channel Output Range
To set the output range for all LTC2672 channels at once, use the Span For All DACs dropdown list. To set the output range for individual LTC2672 channels, use the Span dropdown list for each individual channel (see Figure 5).

Setting the Channel Current Value
To set the output current for all LTC2672 channels at once, use the Current For All DACs (counts) text box. To set the output current for individual LTC2672 channels, use the Current (counts) text box for each individual channel (see Figure 5).

If all channels are in the same range, the user can select the Specify Currents in mA checkbox to specify the currents in mA instead of counts. When the desired span and code are entered, click Write All and then click Update All for the configured current values to appear at the output of all DACs.

To update individual channels, click Write & Update in the individual channel block of the GUI.

For example, in Figure 6, a current of 100 mA is assigned on each channel. When the device is configured, connect a current meter to the desired output channel from the corresponding output turret through the current meter to GND, and click Write All and Update All. The current meter displays 100 mA.

Figure 6. Example Configuration

USING THE SOFTWARE

NORMAL VIEW
When the QuikEval evaluation software initially opens, normal view is shown by default with the Normal View tab selected (see Figure 7). Normal view allows the user to change most settings on the LTC2672 and the settings of each channel with the exception of settings related to the device toggle ability.

Global Controls for Normal View
Note that all controls available in the Normal View tab are also available in the Toggle View tab. See the Toggle View section for controls specific to the Toggle View tab. Specify Currents in mA When the Specify Currents in mA checkbox is selected, the individual Current (counts) text boxes for each channel take values in mA. Otherwise, the input units are in counts. The QuikEval evaluation software converts the mA values to counts using the option selected from the Span For All DACs dropdown list.

Note that values cannot be specified in mA if one or more channels have an individual span setting that does not match the span for all DACs setting because the current is ambiguous in terms of counts in this case.

Current For All DACs (counts)
The Current For All DACs (counts) text box allows the user to set a current value that is sent to all DAC channels. Note that in general, this entered value does not reflect the existing current value of the DACs.

Write All
Click Write All to send a write to all DAC input registers command to the LTC2672 with the value in the Current For All DACs (counts) text box.

Update All
Click Update All to send an update all DAC registers command to the LTC2672. This command sends the value from either Register A or Register B to the DAC output register for each channel, depending on the state of the A/B register bit for that channel and the state of the toggle bit.

Span For All DACs
Select an option from the Span For All DACs dropdown list to send a write span of all DACs command to the LTC2672.

This command changes the span (minimum and maximum output voltages) for every channel.

If one or more channels has a different span, the Specify Currents in mA option is enabled when this command is set, but the Specify Currents in mA checkbox is not selected. To enter values in mA, select the Specify Currents in mA checkbox.

Monitor Mux Channel
Select an item from the Monitor Mux Channel dropdown list to send a monitor multiplexer operation command to the LTC2672. On the DC2903A, the monitor multiplexer output is available at the MUX turret.

To monitor an individual channel, probe the MUX port and select the desired channel from the Monitor Mux Channel dropdown list. The monitored channel box is highlighted in yellow and the Channel x box title changes to indicate that the channel is monitored.

Power Down Chip
Click Power Down Chip to send a power down chip command to the LTC2672 and power down all channels. All Channel x box titles darken and the titles change to indicate that the channels are powered down. The reference and the monitor multiplexer also power down.

Update any or all channels to wake up the updated channel as well as the reference and monitor multiplexer.

Update a powered down channel to wake the channel up again. Controls for Individual LTC2672 Channels in the Normal View Tab

The following labels appear in each Channel x box in the Normal View tab of the main QuikEval evaluation software window.

Current (counts)
Use the scroll arrows or enter a value in the Current (counts)
text box to set the current value that is sent to the LTC2672
during a write command that affects the corresponding
channel. The units are in either mA or counts.

Output
The Output box is a read-only display that indicates the current output in either mA or counts. This value matches the actual measured value at the output of the DAC.

Write & Update
Click Write & Update to send a write to and update (power- up) DAC register n command to the LTC2672 with the value in the Current (counts) text box.

This command causes the corresponding channel output to be the current specified in the Current (counts) box and wakes up the channel if the DAC channel is powered down.

Span
Select an option from the Span dropdown list to send a write span of DAC n command to the LTC2672.

This command changes the span (minimum and maximum output current) for the corresponding channel.

If one or more channels is changed to a span that is different from the other DAC spans, the Specify Current in mA option is disabled and all current numeric entries switch to counts (if
not already measured in counts).

Power Down DAC
Click Power Down DAC to power down the channel. The Channel x box title darkens and the title changes to indicate that the channel is powered down. Update commands wake the channel up again.

Figure 7. QuikEval Evaluation Software Normal View Tab

TOGGLE VIEW

The QuikEval evaluation software allows the user to switch the LTC2672 outputs by selecting the Toggle View tab (see Figure 8). Toggle view allows the user to switch the output channels between Register A and Register B on each LTC2672 channel.

Global Controls for Toggle View

Write All

Click Write All to send a write to all DAC input registers command to the LTC2672 with the value in the Current For All DACs (counts) text box.

This command sends the value to either Register A or Register B for each channel, depending on whether the A/B register bit is set for that channel.

If the A/B register bit for a channel is set, the value is sent to Register B. Otherwise, the value is sent to Register A. Update All Click Update All to send an update all DAC registers command to the LTC2672.

This command sends the value from either Register A or Register B to the DAC output register for each channel, depending on the state of the A/B register bit and the state of the toggle bit for that channel.

If the A/B register bit and the toggle bit for a channel are set, the value is taken from Register B.

If the A/B register bit or the toggle bit is not set, the value is taken from Register A.

A/B Select
Select or clear any of the Bit 0 to Bit 4 checkboxes to send a write to A/B register command to the LTC2672.

Channels with the A/B bit set write to Register B on a write command or write all command.

Channels with the A/B bit set update the DAC register from Register B if the toggle bit is set.

Channels with the A/B bit set update the DAC register whenever the toggle bit (or TGP pin) changes value.

Channels with the A/B bit set wake up when the toggle bit (or TGP pin) changes value when the channels power down.

Toggle Bit
Click the button below Toggle Bit to send a toggle DAC channels command to the LTC2672. The text on the button changes to indicate the state of the toggle bit (High indicates true or set, and Low indicates false or cleared).

The value of the toggle bit is combined (AND’ed) with the TGP pin such that switching the bit is only successful if the TGP pin is tied high, and switching the TGP pin is only successful if the toggle bit is set high.

Switching the bit (or TGP pin) results in the following outcomes. First, the source for the DAC output register changes. If the bit goes from low to high, the source changes to Register B. If the bit goes from high to low, the source changes to Register A.

Second, an update occurs that moves the contents of the new source register into the DAC output register. If Register A is connected to the DAC and the button below

Toggle Bit is clicked, the connection changes so that Register B is connected and the output display populates with the contents of Register B.

Auto Toggle dt (ms)
The value in the Auto Toggle dt (ms) text box represents the rate in milliseconds that the output switches from Register A to Register B when the toggle bit is selected and the auto toggle option is turned on.

Auto Toggle
Click Auto Toggle to cause the button below Toggle Bit to automatically switch at a rate determined by the value in the Auto Toggle dt (ms) text box.

Click Auto Toggle again to turn the auto toggle option off. Controls for Individual LTC2672 Channels in the Toggle

View Tab
The following labels appear in each Channel x box in the Toggle View tab of the main QuikEval evaluation software window.

Current (counts)
See the Current (counts) section of the Controls for Individual LTC2672 Channels in the Normal View Tab section. The functionality of the Current (counts) text box in the Toggle View tab is the same as that of the Current (counts) text box in the Normal View tab.

Write
See the Write & Update section of the Controls for Individual LTC2672 Channels in the Normal View Tab section. The functionality of the Write button in the Toggle View tab is the same as that of the Write & Update button in the Normal View tab.

A
This text box contains a read-only display that indicates the current Register A value in either mA or counts.
B
This text box contains a read-only display that indicates the current Register B value in either mA or counts.

DAC Register
This text box contains a read-only display that indicates the current output in mA or counts.

The value in this text box matches the actual measured value at the output of the DAC.

CONTROLS FOR THE LTC2672 TOGGLE FUNCTION
The LTC2672 has a double buffered output register system that supports toggling between the two input values stored in Register A and Register B. Clicking the Toggle View tab keeps most of the Normal View tab functionality with the added ability to access the input buffer registers. To fill both Register A and Register B, take the following steps in the Toggle View tab:

1. In toggle mode, enter the desired value for Register A in the Current (counts) text box of the desired Channel x box.
2. Click Write to send the data to Register A.
3. Select one of the Bit x checkboxes under A/B Select to indicate the desired channel. Note that the Current (counts) value in the Channel x box is now connected to Register B.
4. Enter a new value in the Current (counts) box for Register B.
5. Click Write to send the data to Register B.
6. Click the Auto Toggle button to change which register feeds the DAC output register and to update the DAC output register. Note that Register B connects to the DAC register and the DAC register receives the value of Register B.
7. Click the Auto Toggle button again to change which register feeds the DAC output register and to update the DAC output register. Note that Register A connects to the DAC register and the DAC register receives the value of Register A.
8. Successive toggles continue to switch the DAC output. Note that leaving the toggle bit high and pulling the TGP pin up and down also switches the DAC output.

Note that switching in the QuikEval evaluation software is only successful when the TGP pin is tied high.

Figure 8. QuikEval Evaluation Software Toggle View Tab

TROUBLESHOOTING

HARDWARE
A comprehensive list of frequently asked questions (FAQ) is available on the LTC2672: FAQ page in the EngineeringZone site. For other questions, please submit them to the precision DACs section of the EngineeringZone site.

EVALUATION BOARD SCHEMATIC

Figure 9. DC2903A Schematic

ORDERING INFORMATION

BILL OF MATERIALS

Table 3. Bill of Materials

ESD Caution

ESD (electrostatic discharge) sensitive device. Charged devices and circuit boards can discharge without detection. Although this product features patented or proprietary protection circuitry, damage may occur on devices subjected to high energy ESD. Therefore, proper ESD precautions should be taken to avoid performance degradation or loss of functionality.

Legal Terms and Conditions

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