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How to read datasheets

Learn how to read datasheets — absolute maximum ratings versus recommended operating conditions, typ versus min/max values, I/O levels and timing, thermal resistance and junction temperature, and key MOSFET and op-amp parameters — with multiple-choice questions.

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How to read datasheets: key points

The datasheet is the most dependable reference when selecting parts and designing circuits. Its numbers, however, cannot simply be used as written. The basics are to distinguish absolute maximum ratings, the limits for avoiding damage, from recommended operating conditions, within which performance is guaranteed; to distinguish guaranteed min/max values from typ values, which are only a guide; and to read the test conditions, such as temperature and supply voltage, attached to each value.

You will also learn input/output voltage levels and noise margin, timing such as setup and hold, and junction-temperature calculations using thermal resistance, as well as how to read the key parameters of MOSFETs, op-amps, regulators and A/D converters, and assembly-related information such as packages, ESD robustness and moisture sensitivity.

All How to read datasheets questions (50)
  1. Which correctly describes the difference between "absolute maximum ratings" and "recommended operating conditions" in a datasheet?
  2. On a prototype board, a surge was found that momentarily pushes the supply voltage above its absolute maximum rating. The IC still works normally afterward. Which is the appropriate way to think about this?
  3. Which correctly describes the concept of component "derating"?
  4. Which correctly describes "typ (typical)" in an electrical characteristics table?
  5. 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?
  6. The top of an electrical characteristics table states "Ta = 25 °C, VDD = 3.3 V unless otherwise noted." Which is a correct point to note when reading this table?
  7. In an electrical characteristics table, what does a footnote saying "Guaranteed by design and characterization; not production tested" mean for that parameter?
  8. 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?
  9. The driving IC has VOH(min) = 2.9 V and VOL(max) = 0.4 V, and the receiving IC has VIH(min) = 2.0 V and VIL(max) = 0.8 V. What is the low-level noise margin?
  10. Which correctly describes the problem with connecting the output of an IC powered from 3.3 V directly to a CMOS input powered from 5 V (VIH(min) = 0.7 × VDD)?
  11. What does it mean when a datasheet describes an input pin as "5 V tolerant"?
  12. Which correctly describes the change when the value of the pull-up resistor on an open-drain output is reduced?
  13. What is the main problem when many CMOS inputs are connected to a single output of a CMOS logic IC?
  14. A microcontroller's operating current is specified as "120 µA/MHz." When it runs at 16 MHz, roughly what is its operating current?
  15. What is the main reason standby current is specified per temperature, such as "typ 0.5 µA at 25 °C, max 10 µA at 85 °C"?
  16. Which correctly describes the "quiescent current (IQ)" of a linear regulator?
  17. What is the main reason a datasheet for an IC with two supplies—1.0 V for the core and 3.3 V for I/O—specifies a power-up sequence?
  18. Which correctly describes what can happen when a 3.3 V signal from another circuit is applied to an input pin of an IC that is not powered?
  19. What is the main reason a datasheet recommends "placing a 0.1 µF ceramic capacitor as close as possible to each supply pin"?
  20. The transmitting IC has a clock-to-output delay of max 6 ns, the board trace delay is 1 ns, and the receiving IC has a setup time of 3 ns. Ignoring clock skew, what is the maximum usable clock frequency?
  21. When checking whether the receiver's hold time is met, which value of the transmitter's clock-to-output delay should be used?
  22. Which is the common definition of the propagation delay tPLH in a logic IC datasheet?
  23. What is the main reason a logic IC's recommended operating conditions specify an upper limit on how slow input rise and fall can be (for example, 10 ns/V)?
  24. In a timing diagram, what is meant by the notation in which an address or data bus is drawn as two parallel lines, upper and lower, that cross in an × shape here and there?
  25. Which is a correct caution when using the θJA (junction-to-ambient thermal resistance) given in a datasheet for the thermal design of real equipment?
  26. An IC with maximum junction temperature Tj(max) = 125 °C and θJA = 50 °C/W is used at an ambient temperature Ta = 85 °C. What is the upper limit on allowable power dissipation?
  27. When estimating the junction temperature of a power device used with a heatsink, which combination should be used as the junction-to-ambient thermal resistance?
  28. Which is the correct use of the ψJT (junction-to-top-of-package thermal characterization parameter) given in a datasheet?
  29. A package's allowable power dissipation is 1.0 W up to an ambient temperature of 25 °C, and above that it decreases linearly to 0 W at 150 °C. What is the allowable power dissipation at an ambient temperature of 75 °C?
  30. A silicon power MOSFET's datasheet gives RDS(on) = 10 mΩ (Tj = 25 °C, VGS = 10 V). Which is the correct approach when using it at around Tj = 125 °C?
  31. Which is correct about a MOSFET with VGS(th) specified as 1.0–2.5 V (ID = 250 µA)?
  32. A MOSFET with total gate charge Qg = 50 nC is driven with a 10 V gate voltage at a switching frequency of 100 kHz. Roughly how much power is needed to drive the gate?
  33. Which is the correct way to read a power MOSFET's safe operating area (SOA) graph?
  34. Which is correct about the reverse recovery time trr in a diode datasheet?
  35. For an op-amp with a slew rate of 0.5 V/µs, roughly what is the maximum frequency at which a sine wave with an amplitude (peak) of 10 V can be output without distortion?
  36. A non-inverting amplifier with a gain of 100 is built using an op-amp with an input offset voltage of max 2 mV. With the input at 0 V, which is the guide for the maximum error voltage that can appear at the output?
  37. The datasheet of an op-amp used on a single 5 V supply gives the common-mode input range as "0 V to (V+ − 1.5 V)." Which is correct?
  38. A 3.3 V output LDO has a dropout voltage specified as max 300 mV (at 500 mA output current). What is the minimum input voltage needed to maintain the output voltage while supplying 500 mA?
  39. An LDO with a PSRR (power supply rejection ratio) of 60 dB at 1 kHz has a 1 kHz, 100 mV ripple on its input. Which is the guide for the ripple appearing at the output?
  40. Which condition is most closely related to the "no missing codes" guarantee in an A/D converter datasheet?
  41. A 16-bit A/D converter has a SINAD (signal-to-noise-and-distortion ratio) of 74 dB. Roughly what is its effective number of bits (ENOB)?
  42. Which is the common pin-numbering convention for packages such as QFP and SOP?
  43. Which is the common way to handle the large exposed pad on the bottom of a QFN package?
  44. A datasheet states "ESD rating: HBM ±2 kV, CDM ±500 V." Which is the correct interpretation of these values?
  45. Which is the correct handling of a surface-mount part marked MSL 3 (moisture sensitivity level 3)?
  46. Which correctly describes what "RoHS compliant" means for electronic components?
  47. What is the main purpose of checking a datasheet's revision history?
  48. Which correctly describes the content of a document called "errata" provided for microcontrollers and similar devices?
  49. Which is the correct way to treat the "Typical Characteristics" graphs in a datasheet?
  50. On a graph with a logarithmic horizontal axis, which value is closest to the one represented by the position exactly midway between the 10 and 100 tick marks?

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