Intelligent power to enhance automated test

From semiconductor fabrication and automotive design and manufacture to the development of communications platforms and medical equipment, the requirement for high-speed, precision testing of increasingly complex applications is rapidly growing. This fuels the need for automated test equipment (ATE) that provides the functionality, accuracy, repeatability and speed needed to deliver consistently reliable results quickly and easily with the minimum of human intervention. In line with this need, programmable power sources have become an essential component of ATE systems.

Programmable power supplies provide an analogue input or digital interface that allows for remote control of supply operation. Providing fine resolution and flexible programming of voltage and current, the latest programmable power supplies help to speed up test cycles by reducing time spent manually setting key voltage or current parameters, performing tests, measuring and waiting for the results and then reconfiguring equipment for the next test. They also support improved measurement accuracy, better repeatability and minimise the possibility of human error. Choosing the right programmable source also allows engineering teams to reduce the number of different power supplies needed in a given test environment. Thanks to these factors, the value of the global programmable power supply market is expected to grow almost 6% year-on-year from 2020 to reach just under a billion dollars by 2025. (Source: The Express Wire).

Figure 1: Advances in performance and increased complexity are driving demand for automated testing equipment (ATE).

Selecting programmable supplies

While specifications vary, there are a number of fundamental factors to consider when choosing a programmable power supply for a given ATE environment:

• Setting accuracy – this refers to the accuracy at which the power supply can be programmed. Setting accuracy determines how close the regulated parameter is to its theoretical value. It is tested by measuring the regulated variable with a traceable, precision measurement system connected to the output of the power supply.

• Setting resolution - also known as programming resolution. It represents the smallest change in voltage or current settings selected on the power supply. The resolution specification limits the number of settable discrete levels and is defined by a combination of user interface digits available, as well as the number of bits in the DAC. 

• Transient response - this reflects the time for the output voltage to return to the programmed state after a disruptive change in load current.

• Load regulation - a classification of voltage regulation. Load regulation determines the ability of an output channel to remain constant during changes in the load. As the impedance of the device under test (DUT) changes, the regulated parameter should not change significantly.

• Ripple - a critical parameter to power supply output. Ripple refers to periodic AC on the output. Current from the ripple voltage may cause heating and damage of capacitors over time, which makes it unsuitable for most sensitive electronics equipment.

• Noise - this covers a broad spectrum, and when viewed in the frequency domain, manifests itself as an increase in the baseline.

• Line regulation – this is another classification of voltage regulation. Line regulation measures the power supply’s ability to maintain its output voltage or output current. In contrast, the AC line input voltage and frequency vary over the complete allowable range. Line voltage and frequency affect the available power to feed the output, especially when drawing maximum current from the supply.

• Temperature stability – while temperature stability can affect a power supply’s performance, the effect of temperature on the output is usually minimal in a stable ambient temperature environment. Accuracy is usually specified as being valid over a particular temperature range, often between 20° and 30°C.

• Readback accuracy - sometimes called meter accuracy. Readback accuracy determines how close the internally measured values are to the theoretical value of the output voltage after setting accuracy is applied.

• Readback resolution - this is the smallest change in internally measured output voltage or current that is discernible by the power supply. It is usually expressed as an absolute value but can also be given as a percentage of full scale.

• Interoperability - test environments rely on products from a wide variety of manufacturers so ensuring interoperability between the supply and other equipment is important.

• Size – few test benches or racks have unlimited space, so form factor is an important consideration.

• Standards compliance – power supplies are subject to a number of international safety and application-specific standards.

Figure 2: The iLS single output programmable DC power supplies.

From analogue to digital

Traditionally, most of the programmable power supplies used in ATE applications have been designed with analogue control loops. Many have digital front panels and digital interfaces for the user, but the control of the power supply is still done with analogue circuits.

Now, sources that offer fully digital control allow users to configure and manage the power supply in ways that are not possible with an analogue control loop. The control loop can be changed in real time, for instance, to accommodate many types of loads. Power supply performance can also be more easily tailored to meet a particular customer’s needs.

For example, the Advanced Energy Artesyn Intelligent Laboratory Series (iLS) of digital, high-power-density, programmable, single output DC power supplies are a small form factor for both benchtop and rackmount applications. The compact, lightweight programmable units incorporate embedded 12-bit DACs and ADCs for measurement and precise reporting of voltage and current. Digital rotary controls enable rapid adjustment and fine-tuning of output voltage and current, while ports offer flexible remote control via digital LXI (LAN eXtensions for Instrumentation) USB and Ethernet inputs or analogue inputs.

The programmable supplies’ patented wireless remote sense capability provide the same levels of accuracy as conventional wired remote sense. At the same time, it feature simplifies installation, improves performance and dramatically reduces the problem of noise by allowing regulation of the DC voltage at the load without the need for noise-sensitive wiring.

The wireless remote sense feature means that, when using the power supply, the only leads needed are the power ones to the load. The system works by sensing the load current and determining the resistance of the leads to the load. Once this data is known, then Ohm’s law can be used to determine the voltage needed on the output of the power supply in order to ensure the proper voltage at the load. As the iLS is a digitally controlled power supply, the system can sense the output current and recalculate the output voltage requirement at the switching frequency of the power supply. As a result, wireless remote sense can respond to variations in the load current much faster than wired remote sense.

The family comprises iLS600 and iLS600-R standalone and rackmount, as well as iLS1500 rackmount single-output power supplies offering 600 and 1500W respectively. This allows users to simulate a broad range of applications. Output voltages range from 30 to 400V, while output currents range from 2.5 to 33A for the 600W units and from 5A to 70A for the iLS1500. The ability to connect up to four units in parallel and two units in series further enhances flexibility to meet a variety of test scenarios.

The power supplies also incorporate over-current, over-voltage and over-power protection (OCP, OVP, OPP) and conform to UL 60950-1, UL 62368-1 and CAN/CSA C22.2 product safety standards. USB and Ethernet inputs are SCPI- (Standard Commands for Programmable Instruments) -compliant and the units are compatible with National Instruments’ LabView software. In the case of the rack-mounted versions, a sophisticated scripting ability allows users to write programs that can be loaded into the power supply for execution on command.