Most embedded systems use more than one power rail and many use four or more, making power-rail test and verification a time-consuming task. As the number of power rails goes past four, using a 4-channel oscilloscope to verify timing in an embedded application can turn into a rather slow process. To the rescue comes the more efficient 8-channel oscilloscope.
It turns out that evaluating power-on and power-off sequences is one of the most common reasons engineers give for wanting more than four channels. In this article, we’ll briefly cover using a 4-channel scope for this purpose, and then we’ll show some examples that take advantage of an 8-channel scope.
Why the Increase in Power Rails?
A single IC, such as an FPGA, DSP, or microcontroller, can require several power rails that may have specific timing requirements. For example, a chip manufacturer may recommend that the core voltage supply stabilize before applying the I/O supply voltage. Or a manufacturer may require that supplies come up within a specified time relative to each other to avoid prolonged voltage differences on various supply pins. The power-on sequence between processors and external memory can also be critical.
Chip manufacturers may specify that particular supplies must come up monotonically to avoid multiple power-on resets. This can be challenging since inrush currents can place high transient demands on point-of-load regulators. In this case, the shape of power-rail startup is as important as the timing sequence.
Combine the various chip supply requirements, bulk supplies, reference supplies, and multiple point-of-load regulators for other ICs in a design, and the design can reach up to seven or eight power rails in a hurry. However, the hurry stops when it comes time to testing and verifying all of these rails. It must be done carefully and methodically for each rail to ensure a successful design.