Introduction: A 99-step List sequence lets a programmable DC power supply repeat voltage and current stress profiles automatically, and the loop count and trigger setting decide how that stress actually runs.
Burn-in and reliability testing rarely means sitting at one voltage for a week and calling it done. Many components need to see a repeating pattern of setpoints — power up, hold, drop, hold, repeat — for thousands of cycles before anyone can say anything useful about them. Done by hand, that pattern is slow and inconsistent, because the profile drifts with whoever is turning the knob. A stored List sequence replaces that hand movement with timed, repeatable output changes, and the engineering value comes from understanding how the sequence is arranged, how it repeats, and what starts it.
What List Mode Changes in Burn-In and Reliability Testing
On a laboratory bench, changing a setpoint is easy: turn the knob, watch the display, wait, turn it again. That works for a handful of cycles. It stops working when a burn-in rack runs for days and the same profile has to land on every unit under test. Operator attention drifts, dwell times drift with it, and two boards tested on different shifts no longer carry comparable histories. List mode changes that by turning the profile into stored data. A programmable DC power supply holds a numbered sequence of steps, each with its own voltage and current setpoint and its own dwell time, and executes them in order without further input. Because the sequence is data rather than a hand movement, cycle two looks like cycle two thousand, and that repeatability is the whole point in burn-in work, where a test's value comes from comparing many units under identical conditions. The second change is timing. In a real stress profile, the transitions matter as much as the levels. A step voltage or step load event exposes a regulator, a connector, or a solder joint to a brief electrical shock, and the recovery behaviour after that event is often what engineers want to observe. Texas Instruments' application note on measuring power supply transient response explains how step changes and recovery are characterised, which is useful background for understanding what a device under test experiences at each transition inside a List sequence. List mode applies a defined stress profile repeatedly and consistently, and the profile's usefulness follows from how closely it matches the physics of the failure under investigation, together with chamber conditions and the way results are measured.
How Steps, Loops, and Triggers Shape a Stress Profile
The character of a List sequence comes from how the steps are arranged, how many times the whole sequence repeats, and what signal or action starts it. Those three choices separate a short characterisation run from weeks of accumulated cycling.
1. Loop Count Converts a Small Step Set Into Long-Duration Stress
A 99-step sequence is a lot of steps, but most burn-in profiles use far fewer and repeat them. Eight or ten well-chosen steps describe a power cycling pattern completely, and the loop count converts that short pattern into hours or weeks of accumulated stress. On a supply that supports loop counts up to 99999, a ten-step pattern looped five thousand times is fifty thousand step transitions, and the practical limit becomes the test schedule rather than the instrument. A short, readable core pattern with a high loop count usually achieves more than filling all 99 steps with slight variations, because a readable pattern stays debuggable when a unit behaves unexpectedly halfway through a run.
2. Trigger Choice Determines Whether the Sequence Runs Alone or Waits for an Event
Trigger selection answers a simple question: when does step one begin? An automatic trigger starts the sequence as soon as it is armed, which suits soak and cycling tests that run unattended. A key trigger starts it from the front panel, which serves setup work and runs that need to align with an external observation such as a thermal image or a scope capture. An external trigger starts it from a signal, which is how burn-in fixtures, handlers, and chambers synchronise the electrical profile with everything else happening in the test. When the supply sits armed and waiting while the fixture has already moved on, the result is a scheduling mismatch rather than a profile error, and the sequence falls out of step with the rest of the bench. Between steps, slope control shapes the edge of each transition. A supply that jumps from one level to the next in microseconds produces a sharper event than one that ramps. An adjustable voltage and current slew rate, such as the 0 to 250 mS/V/A range on some benchtop supplies, softens a transition when a gentler edge is more realistic and keeps it fast when the transient itself is the object of the test. Texas Instruments' material on inrush current and slope control explains why a controlled ramp often suits a device under test better than an abrupt step.
Where a 99-Step Sequence Fits and Where Simpler Control Is Enough
Long sequences earn their place in tests where the profile itself carries information. Multi-rail boards that need a specific power-up order, DC-DC converters that must survive repeated start-stop cycles, connectors and relays cycled under load, and sensors that drift under thermal cycling are all cases where a repeating pattern tells an engineer more than a fixed level ever could. Storing several of these patterns as separate parameter groups also serves a bench that runs three different product families, because the right profile can be recalled instead of rebuilt step by step. A constant output answers the opposite situations. A simple soak at rated voltage, a measurement that needs stable thermal equilibrium first, or a failure mode such as slow leakage that only appears after hours at one level all read more clearly when the supply holds still, because variation in the sequence adds nothing to the experiment and makes the data harder to interpret. Constant voltage or constant current also fits when a sequence would change so often that programming it costs more time than running it. The decision turns on whether the experiment depends on change over time. The MATRIX MPS-1000 series shows how these functions appear on a benchtop instrument: 99-step List output with automatic, key, or external triggering, loop counts up to 99999, 99 parameter storage groups, and an adjustable 0 to 250 mS/V/A slew rate, across a series that covers 0 to 150 V, 0 to 10 A, and 36 W to 360 W. Published ratings for the early models in the range are straightforward, and for MPS-1007 through MPS-1012 the manufacturer's current documentation carries the exact model mapping.
Conclusion
List mode is a timing tool. It converts a hand-tuned voltage or current change into a repeatable sequence, and loop count and trigger choice then decide whether that sequence becomes a short characterisation run or weeks of unattended cycling. Sequence length itself is secondary to how the core pattern, its repeats, and its start condition match the experiment. In burn-in and reliability work, a sequence belongs wherever the profile is the experiment, and a plain constant output belongs wherever it is not. A profile whose step count, loop limit, trigger option, and slew setting agree with the test plan stays synchronised with the test schedule.
FAQ
Q：What is List mode on a programmable DC power supply?
A：List mode is a stored sequence of output steps. Each step holds its own voltage and current setpoint plus a dwell time, and the supply runs through them in order instead of waiting for someone to change the settings by hand. On many benchtop supplies that means a fixed number of steps, a loop count that repeats the whole sequence, and a choice of how the sequence is started.
Q：How do loops and triggers affect a 99-step burn-in sequence?
A：Loop count decides how many times the entire sequence repeats, so a short pattern can generate tens of thousands of stress events without a longer program. The trigger decides when the first step begins: automatically when armed, from the front panel, or from an external signal. Loop count controls duration, while the trigger controls timing and coordination with the rest of the test setup.
Q：When is a simple constant output better than a List sequence?
A：When the test does not depend on changes in the output. Soak tests at a fixed voltage, thermal equilibrium measurements, and slow leakage checks all work better with a stable level, because variation in the sequence adds nothing and makes results harder to interpret. A constant output is also simpler when the profile would change constantly.
Sources / References
Measuring Power Supply Transient Response
Understanding Inrush Current and How to Protect Your Design
No comments:
Post a Comment