Ripple Value for Vcc Rails

[Docara]

Hi

Further to a recent post, I am curious as to any rule of thumb values for 'regulated' power rails which we should aim for.

For example for common 3V3, 5V0 or even 12V0 rails would, say, 1mV, 2mV, 10mV or 100mV be acceptable. If a value is published as a percentage is oh I dunno 1% acceptable, 2%, 5% whatever.

Now I know this depends on the main circuit so I am assuming something like a general purpose MCU doing some switching, reading from a Bus (I2c,SPI, UART) and driving some LEDs, sort off thing NOT a precision instrumentation amplifier trying to detect a Neutrino from the Big Bang!

Thanks

[imo]

The typical ripple you may see in such MCU systems is 5-20mVp-p.

[Ian.M]

If its all digital and the MCU has a wide enough operating Vcc range, even 10% ripple may not cause any problems.  OTOH if it has a 10 bit ADC converter with either the input or the reference relative to the supply rails, even 0.01% ripple is likely to be objectionable.

Also you should distinguish between double line frequency ripple from a conventional linear PSU and high frequency ripple from a switching supply which IMHO is more likely to cause issues (at any particular peak to peak amplitude) due to greater capacitive coupling to sensitive nodes.

[Docara]

Thanks both