In section 1.1 Introduction to DVM: What is DVM? you learned the very basics of the DVM module. In that topic, you ran a number of tests from the built-in testplan. In this topic you will learn how to prepare a schematic for DVM and learn that DVM is capable of far more than the built-in testplan presented in the introduction topic.
This module presents DVM from a new perspecitve - instead of presenting DVM from the program's point of view, the perspective of an experienced SIMPLIS user who has a simulation problem to solve is used. As you will learn, DVM enables an experienced user to solve many problems which cannot be solved by a conventional single-step or multi-step simulation.
To download the examples for the Applications Module, click Applications_Examples.zip
In this topic:
DVM can help you solve many problems including:
The scope of problems DVM can help you solve is wide ranging and limited to your imagination.
In this topic, you will learn the following:
Looking at real and tangible examples is the simplest way to understand what DVM is, and what it can do. Here are five examples.
DVM handles setting up these efficiency tests quite easily.
In this example, the deadtime between the two MOSFETs in a synchronous buck converter is stepped and the efficiency is measured over the entire load range with a fixed input voltage. Two variables are swept - ILOAD and one of the deadtimes, in this case, the delay between turning off the low side MOSFET and the high side MOSFET. The optimum deadtime can be graphically determined on the resulting efficiency curves.
In this example you will see how easy it is to modify the testplan used in the Generating Efficiency Plots with Multi-Step Runs in DVM section to step the deadtime parameter and produce these plots.
DVM has built-in BodePlot() Test Objective which configures the schematic to measure the loop gain, runs the appropriate AC analysis, generates the loop gain plots and finally makes the gain margin, phase margin, and gain crossover frequency measurements. Repeating this test for different line and load conditions generates a series of Bode Plots and in this example, the light load bode plots show a significantly lower loop bandwidth and improved gain and phase margin. This particular circuit enters into a discontinuous conduction mode at light load; therefore, the double pole in the plant splits and the lower frequency pole dominates the bode plot response.
As with the other examples, the scalar values produced from each run can be plotted on a XY axis. This example plots the gain margin, phase margin, and gain crossover frequency versus the load current, with the input voltage as the running parameter. The three curves correspond to the minimum, nominal, and maximum input voltages.
The testplan used to generate these plots uses single step Bode Plot simulation objectives and is taken directly from the built-in testplan for a 1 input/ 1 output converter. Scalar aliases were added to the testplan to generate unique scalar names for each input voltage and a final test extracts the curves from the previous tests and plots the scalar values.
DVM has a built-in sensitivity and worst case analysis tool. This example uses the same synchronous buck converter used to optimize the deadtime. The end goal of this sensitivity analysis is to determine the sensitivity of the converter efficiency to deadtime parameter variation.
One challenge facing VR controller manufacturers is guaranteeing the minimum and maximum output voltage regulation specification is met when the VR is loaded with a repeated pulse load transient of varying frequencies and duty cycles. This example uses DVM to apply a pulse load transient to the converter with the frequency stepped over a range of 1kHz to 1Meg Hz, with a duty ratio of 10 to 90%.
Because the repeated pulsed load is asynchronous to the converter's switching frequency (which might change with applied load current), it sets up a beat frequency at the converter output. DVM captures enough pulse load periods to accurately measure a representative minimum and maximum output voltage for the particular pulse load frequency and duty cycle. The results can then be plotted on a XY plot similar to the previous examples. In this case the pulse load frequency is plotted on the x-axis and the magnitude of the minimum or maximum output voltage is plotted on the y-axis, with the duty ratio as the running parameter. A total of 151 frequencies and 9 duty ratios are simulated, resulting in a total of 1359 simulation steps.