English
Menu

How to read datasheets

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?

  1. A0.1 µV
  2. BAbout 1.7 mV
  3. C0.1 mV
Show answer and explanation

Answer: C. 0.1 mV

Voltage ratios in decibels use 20 log₁₀, so 60 dB is 1/1000. 100 mV ÷ 1000 = 0.1 mV appears at the output. 0.1 µV is the mistake of calculating with 10 log₁₀ (power ratio), and about 1.7 mV is the mistake of dividing 100 by 60. PSRR generally decreases at higher frequencies; even with 60 dB at 1 kHz, some products drop to around 20–30 dB at several hundred kHz. When placing an LDO after a switching regulator, check the PSRR at that switching frequency in the graph.

Practice this topic Back to topic

Books on How to read datasheets Ad

As an Amazon Associate I earn from qualifying purchases.

More How to read datasheets questions

  1. Which condition is most closely related to the "no missing codes" guarantee in an A/D converter datasheet?
  2. 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)?
  3. Which is the common pin-numbering convention for packages such as QFP and SOP?
  4. Which is the common way to handle the large exposed pad on the bottom of a QFN package?
  5. A datasheet states "ESD rating: HBM ±2 kV, CDM ±500 V." Which is the correct interpretation of these values?