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AR# 66793

HSSIO Power Supply basic check list


The power supply quality represents both the basic requirement for proper functionality and a complex set of measurements.

As with other analog signals, the power supply analysis is generally assigned to the most experienced engineer due to the many aspects to be analyzed.

For example, the power supply constraints usually cover not only the DC levels, but also the datasheet absolute maximum limits compliance, power-up power-down sequences, transients, response to load variation, noise measurements and simulations, effects on signals quality, device timing issues, EMC compliance, layout decisions, filtering strategies, package behavior, and more.

A basic check-list can help during the initial analysis, but should be completed with a further review when the device is operative, or is changing its functionalities in order to explore all possible problem sources.

For example, powering down a set of transceiver Quads might seem like a harmless action, but it represents a challenging situation for every power supply because of the extremely quick variation in current demand.


Power Supply basic checklist dedicated to HSSIO

  1. DC Levels according to Datasheet requirements
  2. Power-up and power down sequences, if required
  3. AC Noise (<10mVp-p 10KHz to 80MHz)
  4. Maintains Datasheet Compliance under load transient conditions (Config, reset, rate change, partial or total powerdown or powerup)
  5. Methods for isolating power supply noise sources
    Fundamental frequency crosstalk coupling (i.e. from other circuit/systems)
    Combinational frequency crosstalk coupling (frequency mixed: sum and difference)
  6. Indirect measurement of power noise by signal TIE measurement

Suggested methods

Use 50 ohm probing and coaxial cable connection. Using 50 ohms makes it easy to have a constant impedance for the entire path from the DUT to the oscilloscope input and improves the measurement repeatability.

Band limit the measurement. Limiting the bandwidth will do the following:

  • reduce confusion from out-of-band energy
  • allows for easier detection and interpretation of the measured waveform. (i.e. observing only what matters)
To band limit, use a lowpass filter by using either of the following:

  • an external lowpass filter between the DUT and scope input
  • Math processing function on the oscilloscope (Lowpass filter function)

AR# 66793
Date 04/15/2016
Status Active
Type General Article
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