> The deal with linear regulators is that despite what some internet sources might recommend, you probably shouldn’t be using them in your designs.
Yeah, no.
1. Linear regulators do not introduce voltage ripple and by the nature of being variable resistors, they form a nice low-pass filter with the capacitors around it. For some sensitive designs, you use a switching converter to step down voltage to e.g. 5V, filter it and then use LDO to get it down to 3.3V with even more filtering.
2. Linear regulators are dirt cheap. And for e.g. USB devices drawing less than couple hundred mA @ 5V using a regulator to step it down to 3.3V would be an overkill.
Granted, recent Raspberry Pi Pico (for example) does use a switching regulator (unlike other boards in that form factor), but it also has led to complications with power supply ripple showing in ADC readings.
But sure, if you application needs higher efficiency, steps down by more than ~2V or pushes around a lot of current, switching regulator is a better choice.
And if your device spends a lot of time asleep, linear regulators may beat switching regulators by a LOT.
Leakage current can dominate your design, and switching regulators often have lousy leakage current specs (to be fair, so do a lot of old school linear regulators). Furthermore, switching regulators often have to "spin up" while a linear regulator is just sitting there ready to go as soon as your MCU switches on.
In addition, switching regulators tend to be designed for higher currents and tend to have terrible efficiency at small currents (< 1mA). If your circuit uses a very small amount of current even when active, a linear regulator may be superior even for constant-on systems.
Nowadays you can pretty easily find switchers with sub-100nA quiescent current + leakage, e.g. TPS62840 (of course, that's assuming you're at room temperature... FETs at high temperature are all crap for leakage). I note you get 80% efficiency at 1uA out on this device with a 3.6V to 1.8V stepdown config; beats the LDO by a lot, particularly if you spend a lot of your time at uA load currents.
Issue with a lot of these and switching regulators is off chip inductors, which take up space. In small form factors, SOCs etc, you need to use charge pumps and LDOs for internal analog/mixed signal voltages.
Are there chips doing that but buck-boost ? I know there are for "normal" current range, but I haven't found anything super low power
Use case: I want to just have a solar panel + supercap into microcontroller for IoT stuff so I want to suck that cap dry and avoid batteries for temperature range reasons.
Oh, wow, it's even in stock, thanks. I was looking for something like that some time ago but back then only BQ25570 really fitted (and was overkill and a bit more pricy for that)
I built all the low voltage MCU based electronics for my team's solar race cars in college. Power efficiency is a huge deal for a solar powered race car. One of the first pieces I designed was a standalone switching regulator PCB with a 3 pin interface, then made many dozens of them. I then used them in all of my other boards.
Years later after I graduated and left the team, I heard that the folk that took over went through and replaced all the switching regulators with linear ones. I asked them why, and they said someone told them the quiescent draw was lower for linear regulators. I asked them if it was really worth the significantly reduced efficiency dropping from 12V to 3.3V, and they didn't seem to understand what I was talking about. Oops!
The eagle file is probably rattling around somewhere on my hard drive. It was back in 2005 or so, though. I had very little idea what I was doing back then. I just followed the reference schematic from the switching IC's datasheet. It had the IC, an inductor, and some size 1206 resistors and capacitors.
One can purchase $0.15 TI parts have <0.4mA quiescent current and output 3A. These things draw so little under no/low load circumstances that my cheaper 4-digit readout benchtop supplies cannot detect any draw.
0.4 mA quiescent current is huge for very low-power designs though. If your system must spend the majority of its time consuming very little power, that level of constant current draw is a non-starter.
TPS7A20 is 6.5uA, $0.10/ku. TPS7A05 is 1uA, $0.19/ku. It's not that hard to do better than 400uA!
And if you don't mind coughing up when it counts... TPS7A02 is 25nA, $0.45/ku. Triple the price, but more than four orders of magnitude better leakage.
If money is no object, there are some interesting chips out there. The LTC3335 chip[0] is a buck-boost that claims to have a 680nA Iq. Not as low as the TPS7A02, but it looks like it could make up for that in efficiency if your design does anything other than sleep.
Maybe 300mA order of magnitude is more common than 3A, but it's not inconceivable. Lots of designs wake up, burst some RF data at a few hundred mA transceiver load for a few tens of microseconds, then go back to sleep for another few seconds. There are some long-interval scientific instruments that need high-speed ADCs or DACs on battery power in remote locations, which might get into higher current than a few hundred mA. Some deep space crafts can sleep at very low power and run their transmitters at comparable currents. It's very situational.
Older cell phone standards used to burst to about 2.3A upon initial connection to a tower before the tower told the handset to dial it back. I don't know about modern cell phone standards.
Linear regulators also have a start-up time, and its usually somewhere in the datasheet. All feedback loops have some kind of settling response time depending on the bandwidth of the loop, and you'll see that behavior both on start-up and if there's any kind of disturbance, like the load changing.
Yeah. I use a lot of linear regulators. And they have even more advantages. For example, they are simple. They do exactly what you think they do. They don't leak. They don't create noise. They convert voltage right away and you don't need to wait for it to stabilise. And they have simple failure modes. You just throw in one part and it magically converts voltages. What simpler thing you would really want?
In most realistic designs you put multiple power supply rails in your designs because you need a lot of parts that don't need a lot of power but have different voltage requirements or might need voltage offset. In those cases linear regulators are perfect solution.
More than that, those power supply rails usually have standard voltages and there exist standard linear regulators that output those voltages to make everything even easier.
My strategy is to use linear regulators default and only use anything more complex on those voltage rails where I need to step the voltage up or where the inefficiencies would affect my design's performance significantly enough for me to care.
Oh, and use voltage dividers if you want to convert signal levels (unless it is fast signal and you care about signal integrity).
The other place where I see a lot more linear regulators is inside ICs!
Working in Mixed Signal ICs and IP I see a lot of linear regulators.
Inductors are huge and (generally) off chip. If say your SOC has an AMS components, and PINs are a commodity, then you can't use anything but a Charge Pump and LDOs.
Yeah, no.
1. Linear regulators do not introduce voltage ripple and by the nature of being variable resistors, they form a nice low-pass filter with the capacitors around it. For some sensitive designs, you use a switching converter to step down voltage to e.g. 5V, filter it and then use LDO to get it down to 3.3V with even more filtering.
2. Linear regulators are dirt cheap. And for e.g. USB devices drawing less than couple hundred mA @ 5V using a regulator to step it down to 3.3V would be an overkill.
Granted, recent Raspberry Pi Pico (for example) does use a switching regulator (unlike other boards in that form factor), but it also has led to complications with power supply ripple showing in ADC readings.
But sure, if you application needs higher efficiency, steps down by more than ~2V or pushes around a lot of current, switching regulator is a better choice.