3 ms·

I think 100nF is arguably still a safer option for people that are just going to copy the datasheet. As mentioned at the end of the post, lots of low inductance

I think 100nF is arguably still a safer option for people that are just going to copy the datasheet. As mentioned at the end of the post, lots of low inductance capacitance can reduce the phase margin of your linear regulators, and you can very quickly end up with a hundred decoupling caps on a small board. This is of course a solvable problem and sometimes it's just not a problem at all, but it's horrendously difficult to determine when it's going to start being a problem in many cases with big, low inductance power planes and caps littered across them various distances away from each other and the regulator.

exmadscientist 2y ago
The solution is to additionally stuff a bigass electrolytic capacitor on the rail, either tantalum or aluminum. The ESR of the electrolytic will damp out the naughty high-Q tendencies of the ceramics and everything will work out wonderfully in typical cases. (Of course there are pathological cases out there. There are always pathological cases. And if there ever stop being pathological cases, I'll be out of a job!)
- AnthonBerg 2y ago
  At this point—thank you!—a Zachtronics game was born in my head. I’d like to play it! (Maybe it’s a good secret level in that Zachtronics game about nondeterministic infinitesimals portrayed as getting things done in a corporate environment;… what was the name of that one again?)
mort96 2y ago
Having more decoupling capacitance on the board will increase inrush current as well, as all the capacitors have to be charged up once power is connected. Using larger decoupling capacitors than necessary might mean you'll have to add measures to decrease inrush current where you'd otherwise not need to.
- deleted 2y ago
  [deleted]
- dragontamer 2y ago
  Softstart is often good design though and shouldn't be too hard anymore. How many circuits cannot afford 100us of softstart? I guess to your point though: 100uF of capacitance (because of a lot of 10uF caps) to 3.3V requires a 3.3Amp softstart over those 100us startup time. So you still can't go crazy spammy. While 100x 100 nF caps is only 10uF all together.

exmadscientist 2y ago

The solution is to additionally stuff a bigass electrolytic capacitor on the rail, either tantalum or aluminum. The ESR of the electrolytic will damp out the naughty high-Q tendencies of the ceramics and everything will work out wonderfully in typical cases. (Of course there are pathological cases out there. There are always pathological cases. And if there ever stop being pathological cases, I'll be out of a job!)

AnthonBerg 2y ago
At this point—thank you!—a Zachtronics game was born in my head. I’d like to play it! (Maybe it’s a good secret level in that Zachtronics game about nondeterministic infinitesimals portrayed as getting things done in a corporate environment;… what was the name of that one again?)

mort96 2y ago

Having more decoupling capacitance on the board will increase inrush current as well, as all the capacitors have to be charged up once power is connected. Using larger decoupling capacitors than necessary might mean you'll have to add measures to decrease inrush current where you'd otherwise not need to.

deleted 2y ago
[deleted]
dragontamer 2y ago
Softstart is often good design though and shouldn't be too hard anymore. How many circuits cannot afford 100us of softstart? I guess to your point though: 100uF of capacitance (because of a lot of 10uF caps) to 3.3V requires a 3.3Amp softstart over those 100us startup time. So you still can't go crazy spammy. While 100x 100 nF caps is only 10uF all together.