Match the package with its characteristic.
1. DIP 2. QFN 3. BGA
P. Connections beneath the body on a grid Q. Through-hole and socketable R. Leadless pads on the underside edge
Answer: A
The three represent three eras and three assembly requirements: a socket and an iron, a reflow oven with a good stencil, and a full surface-mount line with X-ray inspection. The choice constrains who can build the board.
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The absolute maximum ratings section of a datasheet gives
Answer: B
Nothing is guaranteed to work at an absolute maximum; it is the boundary of survival. The recommended operating conditions are the range within which the electrical characteristics hold, and designing to the absolute maxima is a classic beginner's error.
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A part specified for a 1.8 V to 3.6 V supply is to run from a single lithium cell falling to 2.7 V. The supply is
Answer: C
A cell falling from 4.2 V to 2.7 V stays inside a 1.8 to 3.6 V window for most of its discharge, though the top of a freshly charged cell exceeds it and needs attention. Running direct from the cell over the remainder saves a regulator and its quiescent current.
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The industrial temperature grade of a microcontroller usually spans
Answer: D
Correct answer: \( -40 \) to \( +85 \) \( ^\circ \)C
The four common grades run commercial 0 to +70, industrial −40 to +85, extended or automotive AEC-Q100 grade 1 −40 to +125, and military −55 to +125. Industrial is the one to know because it is the default for anything not in a controlled indoor environment, and the step to +125 usually costs a different die or at least a different price.
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Selecting a commercial-grade part for equipment mounted outdoors is unwise because
Answer: A
Nothing is guaranteed below zero degrees, and while many parts work colder, nothing obliges any particular unit to. Sealing is a matter for the enclosure, and endurance and longevity are separate concerns from the temperature grade.
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A part draws 5 mA running and 2 \( \mu \)A in sleep, and is awake 1 per cent of the time. The average current is about
Answer: B
One per cent of five milliamperes is fifty microamperes, and the sleep current adds very nearly another two, giving fifty-two. Note that the sleep term matters once the duty cycle falls below about a tenth of a per cent.
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At that average current of 52 \( \mu \)A, a 220 mAh cell would last about
Answer: C
Dividing 220 milliampere hours by 0.052 milliamperes gives about 4230 hours, some six months. Self-discharge of the cell and the quiescent current of any regulator have still to be subtracted, and both are often comparable with the load.
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Which change would give the largest reduction in the average current of that design?
Answer: D
The running term is fifty of the fifty-two microamperes, so only attacking the duty cycle matters much. Raising the clock does shorten the awake period but usually raises the current in proportion, leaving the energy per task nearly unchanged.
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A part quotes 200 \( \mu \)A/MHz running. At 48 MHz the running current is about
Answer: A
Correct answer: 9.6 mA
\[ 200\ \mu\mathrm{A/MHz} \times 48\ \mathrm{MHz} = 9600\ \mu\mathrm{A} = 9.6\ \mathrm{mA}. \] The figure is quoted per megahertz because dynamic current scales with clock frequency, so it lets any operating point be estimated from one number - and it is why halving the clock roughly halves the running current, which is the first move in reducing consumption.
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The unit price of the microcontroller is often a small part of the true cost because
Answer: B
Ten thousand pounds of engineering time spread over a thousand units is ten pounds a unit, which dwarfs a two pound part. At a million units the arithmetic reverses entirely, which is why volume changes the whole character of the decision.
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