Safe Operating Area Testing

In this topic:

Overview

Safe Operating Area (SOA) is not a separate analysis mode, but a feature that can be enabled with DC or Transient analyses. With SOA testing, you can set maximum and minimum limits for any simulation quantity and the simulator will display when those limits are violated.

To use SOA testing, you must do two things:

  1. Define the SOA limits for the models or devices you are using.
  2. Enable and configure SOA testing.
Item 1 above is covered in detail in the Simulator Reference Manual - see section titled Simulator Reference Manual/Command Reference/.SETSOA and also the LIMIT parameter described in the section titled Simulator Reference Manual/Command Reference/.MODEL. Setting up simple limit tests using some simple schematic symbols is described below.

Defining Simple Limit Tests

Schematic Symbols

Three schematic symbols are provided that allow the definition of simple limit tests that report the following:

  1. Over and under voltage on a single node.
  2. Over and under current on a single device pin.
  3. Over and under differential voltage on a node pair.
Use the following menus to place these devices:
  • Place > Probe > Watch Voltage
  • Place > Probe > Watch Current
  • Place > Probe > Watch Differential Voltage
Each of these symbols can be edited in the usual way. Each has three parameters that specify
  1. The minimum limit. Use a large negative number (e.g. -1e100) if you don't wish to specify a minimum limit.
  2. The maximum limit. Use a large positive number (e.g. 1e100) if you don't wish to specify a maximum limit.
  3. A label. The default value is %REF% that will resolve to the device's part reference. You can enter any literal value instead.

Setting Up SOA Testing

  1. Select menu Simulator > Choose Analysis...
  2. Select the SOA tab.
  3. Under SOA mode choose either Summary output or Full output. In summary output mode, only the first violation for each SOA device will be reported. In full output mode, all violations are reported.
  4. In Results to: choose where you would like the results reported. Note that writing results to the message window is a time consuming operation and you avoid selecting this option if you are expecting a large number of violations.

Running Simulation

Run the simulation in the normal way. If there are any violations, the results will be reported in the location or locations specified in the Results to: section.

Advanced SOA Limit Testing

The simulator control .SETSOA allows much more sophisticated definitions for SOA limits. In particular, you can define limits for all devices belonging to a specified model. Suppose that you are using a BJT model that has a Vcb limit of 15V. While you could place a differential voltage watch device across each instance of this model, this would be time consuming and error prone. Instead, you can define a single .SETSOA control that refers to the model name of the device. The simulator will then automatically set up the limit test for every instance of that model.

You would usually enter a .SETSOA control in the schematic editor's F11 window. See Manual Entry of Simulator Commands for details. Refer to Simulator Reference Manual/Command Reference/.SETSOA for details about .SETSOA .

It is also possible to set up an SOA specification for a model within the .MODEL control. Again, see Simulator Reference Manual/Command Reference/.MODEL.

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