DVM Principles

Schematic Prepared for DVM:

1. To use DVM you need a schematic and a Testplan. Built-in testplans for common converters, such as a DC/DC converter with a single input and output are included in DVM.
2. DVM uses special DC Input Sources, AC Line Input Sources, and Output Load symbols where the electrical subcircuit used in the simulation can be changed for each test in the testplan.
3. The 3 and 4 pin output load subcircuits include the AC perturbation source for a Bode Plot analysis.
4. DVM keeps track of these special source and load symbols with a system of Managed Sources and Loads, where the source and load reference designators are stored on the control symbol.
5. When using symbolic values, the schematic stores the numerical values on the DVM Control Symbol and the testplan refers to those values using symbolic references.

Testplans:

1. Testplans are nothing but tab-delimited ASCII text files which you edit in a spreadsheet program.
2. Each row in a testplan is a test to be executed, each column defines an action for that test.
3. Testplans can use Symbolic Values to represent the input voltage or output load levels, which greatly simplify the reuse between schematic designs.
4. Objectives are predefined test configurations which define:
   • The source and load subcircuits.
   • The analysis type, e.g. Transient, POP, AC.
   • The post-simulation measurements to be make as well as any additional curves to create.
5. Scalar measurements made by DVM can be selected on the DVM Control Symbol dialog.

Exercise #1: Add an Input Source Symbol

To add the input source, follow these steps:

1. Open the apps_d_0_llc_converter_efficiency.sxsch.
2. Delete the DC voltage source VIN on the left side of the schematic.
3. From the parts selector, choose DVM > Sources > DVM Input Source, and place the symbol where you removed the DC source VIN.
4. Add and remove wires to connect the source as shown below:

Exercise #2: Add a 3-Terminal Output Load Symbol

The 3 and 4-terminal DVM output loads have a SENSE (3-terminal) or a differential SENSE (4-terminal) connection. These extra pins allow DVM to include the injected AC perturbation source and Bode plot probe that are required for closed-loop AC analysis. DVM automatically inserts these components into the load subcircuit definition for the Bode plot tests. For this circuit you will use the 3-terminal output load.

To add the 3-terminal output load, follow these steps:

1. Delete the RL resistor and VAC source from the right side of the schematic.
2. From the parts selector, choose DVM > Loads > DVM Output Load - 3 Terminal, and place it where you removed the load resistor RL. You will need to mirror the symbol about the vertical axis using the F6 key before placing the symbol.
3. Connect the SENSE terminal on the DVM 3-terminal output load to the feedback network.
   Note: The SENSE terminal provides the output voltage feedback information to the converter control loop. During Bode plot tests, the small signal AC source is inserted between the positive load terminal and the SENSE terminal and perturbs the control loop. For all other test objectives, the SENSE terminal is shorted to the positive output terminal of the load. The schematic should appear as shown below:

Exercise #3: Add the DVM Control Symbol

To place a DVM control symbol, follow these steps:

1. From the parts selector, choose DVM > Control Symbols > Full Power Assist DVM Control Symbol.
2. Place the symbol at the top of the schematic.

It is important to note that when you place the DVM Control Symbol after placing the source and load symbols, DVM performs a number of housekeeping tasks. These include:

• DVM detects the input source and output load symbol(s) and configures the DVM Control Symbol accordingly. DVM supports up to five input sources and six output loads. You can add loads or sources at any time.
• DVM automatically reads the analysis parameters from the F11 window and adds these parameters to the DVM Control Symbol.

Exercise #4: Enter Circuit Specifications

When you placed the DVM Control Symbol, the program detected the input source and output load symbols and configured the control symbol with one managed input source (V1) and one managed output load (I1). The program also read in the analysis directives you set in the Simulator > Choose Analysis... dialog, these directives were copied onto the control symbol. Since the program has no way of knowing what the input and output voltages and load currents are, you need to change these parameters to suit this particular circuit.

To change the circuit specifications, follow these steps:

1. Double click on the DVM control symbol.
   Result: The SIMetrix/SIMPLIS DVM Control Panel opens.
   
2. On the Circuit Specifications page, set the values as listed in the following table.

   Parameter	Value	Units
   Circuit Name	test_llc_converter
   Circuit Description	LLC Converter
   Switching Frequency	85k	Hz

   Note: Leave the default values for the other fields on this page.
3. Click on  DC Input in the page-selection box on the left side of the control panel, and then enter the values listed below.

   Parameter	Value	Units
   Voltage
   Nominal	380	V
   Minimum	360	V
   Maximum	400	V
   Misc.
   Source Resistance	0	Ohm

4. Click on Output in the page-selection box, and enter the values listed below.

   Parameter	Value	Units
   Voltage
   Nominal	24	V
   Tolerances
   Peak to Peak	120	mV
   Current
   Maximum	5	A
   Light Load
   @ Vin Min	0.5	A
   @ Vin Max	0.5	A

   Note: Leave the default values for the other fields on this page.
5. Click on the POP Analysis entry to bring up the POP page.
6. Verify that Use "Pop Trigger" schematic device is checked.
7. Click Ok to save the specification changes.
8. Save the schematic as test_llc_converter.sxsch.
   Result: At this point, the schematic is configured to run the built-in testplans which use symbolic values and the DVM source and load subcircuits. A per-prepared schematic at this state is included in the zip archive with file name: apps_d_1_llc_converter_efficiency.sxsch.

Exercise #5: Run a Bode Plot Test

1. Open the test_llc_converter.sxsch schematic you created in Exercise #4, or the apps_d_1_llc_converter_efficiency.sxsch schematic from the zip archive, if you didn't complete the previous exercise.
2. Run the built-in DC/DC 1 Input/1 Output testplan using the menu: DVM > Built-In Testplans > DC-DC (1 Input, 1 Output)
   Result: A test selection dialog appears as follows:
3. Select the third test - AC Analysis > Bode Plot > Vin Nominal > 100% Load
4. Click Ok
   Result: DVM configures the schematic for a Bode Plot test, which includes:

   • Setting a POP and AC analysis for the simulation run.
   • Configuring the input source to be a DC source.
   • Configuring the output load to be a Bode Plot type load which includes loop perturbation and a Bode Plot probe.
   • Applying the measurements to the input source and output load. The load measurements include gain crossover frequency, gain margin and phase margin.

Exercise #6: View Built-in Testplan

In the previous exercise, you ran a single test out of the DC/DC (1-input, 1-output) testplan. When you ran that testplan, a copy of the testplan was made and saved to your schematic's working directory. You can now use this copy as a template or a starting point for defining custom tests. To open this copy in Microsoft Excel,

1. Open Microsoft Excel.
2. On the test_llc_converter_efficiency.sxsch schematic, right click on the gray title bar where the filename is displayed in bold.
   Result: The following context menu is displayed:
3. Select the Open containing folder menu item.
   Result: A Windows Explorer window opens in the schematic's directory, Applications_Examples.
4. In the Windows Explorer window, scroll down to the dvm_builtin-dcdc_1in_1out.testplan file.
5. Drag and drop this file into Excel.
6. You may be presented with an import wizard dialog. If so, select tab delimited and click Ok on the other import dialog pages.

Comment Rows

As long as the first character in the line is a *, you may change the text in these line without affecting DVM operation.

The Header Row

The next row is the extremely important header row. The header row tells the program what type of entries to expect in fields for the following rows. It is assumed that all electrical tests are entered below the header row. Here is the header row and we will examine this in more detail:

1. The first entry:

   *?@ analysis

   The Analysis column allows you to either explicitly set a simulation analysis (.POP. .TRAN, etc) or in this case the Ac placeholder is used. This column is not strictly needed for the built-in testplans.
2. The second entry:

   objective

   tells the program to expect one of the predefined test objectives. In this example, a BodePlot() Test Objective which measures the loop response of the circuit.
3. The third entry:

   source

   can be used to modify subcircuit type used for a source, or to set the amplitude of a source.
4. The fourth entry:

   load

   like the source column, you can change the subcircuit type for a load or change the load value with this column.
5. The fifth column is the test Label. The label is electrically inactive and is used to populate the test selection dialog.

A couple of comments are in order and some conclusions can be made from this testplan header row.

The Vin Nominal, 100% Load Bode Plot Test

Now that you know the purpose of the header row, you will learn what actions are performed for each field entry for the test you just ran, the nominal input voltage, 100% load Bode Plot test. In the table below, the header row and the Bode Plot test row are duplicated for clarity.

1. The first entry:

   Ac

   is a placeholder, and tells DVM to expect a valid AC test ojective in a following Objective entry.
2. The second entry:

   BodePlot(OUTPUT:1)

   tells the program to run a Bode Plot test on the symbolic reference designator OUTPUT:1. This actual reference designator (I1) is stored on the DVM control symbol. OUTPUT:1 literally means "Find the first output load reference designator on the DVM Control Symbol and substitute that reference designator here." The test objective does most of the work for this test. The BodePlot() Test Objective performs these actions:
   1. Sets up a POP and AC analysis for the circuit. The simulation parameter values are taken from the DVM Control Symbol.
   2. Configures the input source to be a DC Input Source.
   3. Configures the output load to be a Bode Plot Load - Resistive Load, and this load contains the AC perturbation source and Bode Plot probe.
   4. Sets up the measurements for the Bode Plot test, you elect which measurements to make on the input sources, output loads, and the AC Bode Plot curves in the DVM Measurements dialogs. These measurements are stored on the DVM Control Symbol.
   5. Finally, the BodePlot() test objective sets the specification checking for the test. For the Bode Plot test, there are two specifications - Gain Margin, and Phase Margin. You define both specification values on the DVM Control Symbol.
3. The third entry:

   Source(INPUT:1, Nominal)

   uses the INPUT:1 symbolic reference designator, and this entry does only one thing: it changes the amplitude of the first managed source. The symbolic value Nominal is read from the DVM Control Symbol. It should be noted that the Source() Function doesn't change the subcircuit type - that was changed by the test objective in a previous column.
4. The fourth entry:

   Load(OUTPUT:1, 100%)

   like the source column, this entry changes the load current, in this case, the Load function changes the value of the load to 100% of the full nominal load current. You set the full load current on the DVM Control Symbol for each output.
5. The fifth entry:

   Ac|Bode Plot|Vin Nominal|100% Load

   defines how the test will be displayed in the test selection dialog. The pipe(|) characters define levels of hierarchy in the test selection dialog:

In this section you learned how the header row works in combination with a row which defines a single test. In the next section, an animated slideshow describes the test actions on a column-by-column basis for this particular test.