Wednesday 28 May 2014

Test instruments form heart of semiconductor test rig!

Test instruments supplied by Yokogawa form the heart of an automated test rig developed by a major European semiconductor manufacturer for evaluating the company’s latest generation of power management chips.

These semiconductors are typically used in energy-efficient power supplies for applications such as LED lighting, motor control and ballasts for energy-saving lamps. A typical 8-pin power management device contains a controller with firmware to control the overall circuit, numerous protection functions and a PWM (pulse width modulation) circuit to control the power switch.
To ease the development of end products using these devices, the semiconductor manufacturer offers its customers “evaluation maps” for a number of standard applications. These not only demonstrate the capabilities of a semiconductor device: they also serve as a basis for customers developing their own applications. The company also uses these maps as an aid to the design and evaluation of the semiconductors: in particular, the various tests that are needed to specify the hardware and software functions of the controller ICs.

Because of the increasing complexity of the controller and the ever shorter development cycles, these tests have to be specified during the actual development of the semiconductor device. In the further phases of the development process, the tests have to be repeated as the hardware or firmware changes in order to verify the correct functioning of the chip.

The company needed to develop tests that could be carried out as automatically as possible – while also creating individual test procedures that could be used over and over again for a variety of projects, applications and components. Depending on the end requirements, these individual tests could then be combined in different configurations.

“As part of a pilot project, we are developing a set of universal individual tests, a multi-purpose test and a higher-level framework with software tools, workflows, and a repository. Later we want to transfer this concept to other applications”, says the Project Manager for the automated test framework.

The individual tests are mainly created in LabView, with each section checking a function or performing specific measurements. The test cases are designed to be as generic as possible, so that the developer only has to specify the parameters for the test. The tests are usually structured to produce only “pass” or “fail” results. For a voltage measurement, for example, the user has to ensure that there is only one test point, and then specify a date and an upper and lower voltage value as a parameter. How and what this measurement consists of is defined in the test case. This not only leads to ease of use: it also means that there is a high degree of reusability of the various test modules involved.

The actual tests are carried out on a “universal” test rig using largely standardised test procedures. Since the test objects are usually relatively simple, the test set-up consists of only a few components. These include a Yokogawa DLM4000 8-channel oscilloscope, a Yokogawa WT3000 power analyser, an AC source and a load. The devices are connected via a USB bus, GPIB interface or Ethernet network to a controller.

The DLM4000 oscilloscope features eight analogue channels in addition to over 24 digital channels, allowing the input and output voltages to be detected and displayed alongside the output current and some digital signals. As a result, the various signals can be checked for faults and parameters can be measured in the time domain.

“Yokogawa has a long history of producing oscilloscopes with features that lead to rapid results, such as cursor measurements with pulse width modulation”, says the manufacturer: “With the WT3000 power analyser, the input and output power, harmonics and flicker are measured and a pre-compliance test is performed. This gives the developer a first insight into whether the circuit complies with standards and regulations in areas such as noise emission.”

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