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How to read datasheets

A load switch (an IC that turns a power rail on and off) has a current limit specified as min 1.0 A, typ 1.5 A, max 2.2 A. You want to draw up to 1.2 A for the load. Which judgment is correct?

  1. AThe typ value is 1.5 A, so there is 0.3 A of margin and it can be drawn without problems
  2. BIt is about half the max value of 2.2 A, so it can be drawn without problems with ample margin
  3. CSome units may enter current limit near 1.0 A, so there is no guarantee that 1.2 A can be drawn
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Answer: C. Some units may enter current limit near 1.0 A, so there is no guarantee that 1.2 A can be drawn

The current limit varies from unit to unit over 1.0–2.2 A; with a unit near 1.0 A, current limiting kicks in as soon as you try to draw 1.2 A, and the output voltage drops. To be sure the required current can always be drawn, choose a part whose minimum current limit (1.0 A) is greater than the load current. Conversely, use the max value of 2.2 A when estimating the current that can flow under fault conditions. Judging by the typ value leads to problems where the prototype works but some units fail in mass production.

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  2. In an electrical characteristics table, what does a footnote saying "Guaranteed by design and characterization; not production tested" mean for that parameter?
  3. A voltage of 1.4 V is applied to an input of an IC whose input thresholds are specified as VIH(min) = 2.0 V and VIL(max) = 0.8 V. How is it interpreted?
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