Looking for *actual* LDO in SOT-223 package - Page 1
Forum section: electronics / general

author: jayx
author_rank: Regular Contributor
timestamp: August 20, 2024, 08:31:01 pm
content: I was quite surpriced to find AMS1117 "LDO" to have 1.1V dropout voltage. Searched for other LDOs and found most of them to be pretty much the same, which tells me that they are just standard voltage regulators with bipolar transistors, not actual LDO with mosfet.Can anyone suggest a proper LDO in SOT-223 package?

author: globoy
author_rank: Frequent Contributor
timestamp: August 20, 2024, 08:58:36 pm
content: They exist. The first one I found at TI - the TLV1171 - boasts a 455 mV drop out @ 1A for Vout=3.3V. It uses a MOSFET pass transistor and is in a SOT223 package.Maybe something here for you:https://www.ti.com/power-management/linear-regulators-ldo/products.html#2954=SOT-223&238max=-18%3B7&But you didn't specify any parameters so maybe they don't exist for your input voltage range or something else?

author: youngda9
author_rank: Regular Contributor
timestamp: August 20, 2024, 09:27:06 pm
content: Digi-Key or Mauser search feature is your friend.

author: jayx
author_rank: Regular Contributor
timestamp: August 20, 2024, 09:37:55 pm
content: Sorry, should have mentioned, parameters like AMS1117: Vout=3.3V, current 1A (minimum 800mA).TLV1171 looks good, thanks globoy. It actually needs to be TLV1117LV33DCYR to be pin compatible with AMS1117.

author: thm_w
author_rank: Super Contributor
timestamp: August 20, 2024, 10:57:31 pm
content: LDO means low dropout. Its not a strict definition of the topology.1.1V IS low compared to the old school 2-3V+ dropout regulators. Its just that modern implementations are even lower now, and we have come to expect that.From TI:"There are two types of linear regulators: standard linear regulators and low dropout linear regulators (LDOs). The difference between the two is in the pass element and the amount ofheadroom, or dropout voltage, required to maintain a regulated output voltage."https://www.ti.com/lit/ml/slup239a/slup239a.pdf?ts=1724134289735

author: Siwastaja
author_rank: Super Contributor
timestamp: August 21, 2024, 08:30:19 am
content: Quote from: edavid on August 20, 2024, 10:07:15 pmNo, it literally means low drop-out, and is sometimes (although quite rarely) used even with very different topologies e.g. in switch mode converters.However as OP has figured out, the industry's definition of what is "low" is quite archaic. 1.1V dropout seemed low in 1970-1980's when "standard dropout" regulators dropped between 2-3V.Today I always try to advice not to use 1117: it has high drop out, is quite sensitive to output capacitance value and ESR so easily becomes an inadvertent oscillator, and it's second sourced from gazillion of manufacturers with different stability requirements, and counterfeit to no end. Instead, if low dropout is not important, use something even more archaic with standard dropout, e.g. 78xx has easier stability requirements. Or, if low dropout matters, pick a modern-day regulator instead. Look at the datasheet for words like "stable with MLCC output capacitor".

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 21, 2024, 08:35:42 am
content: Mind that a lot of distributors don't sell them as "LDO" anymore at all, categorizing all linear regulators that way. So the term has lost all meaning, despite the abbreviation still being well known.Offhand, consider NCV4274 family, several Microchip (formerly Micrel) e.g. MIC1703, 5209, 2954, and many others.Tim

author: Chalcogenide
author_rank: Regular Contributor
timestamp: August 21, 2024, 08:42:55 am
content: STM's LDL1117 is an AMS1117 direct replacement that has 350 mV typical (600 mV max) dropout at 1.2 A and is stable with ceramic capacitors.

author: jayx
author_rank: Regular Contributor
timestamp: August 21, 2024, 08:20:31 pm
content: Thanks all for suggestions. Last time I've used linear regulator was quite long time ago, when LDOs were not commonly available. Only recently needed one with sub 1V dropout and after reading mentioned TI paper I've wrongly assumed that all LDOs have FET pass element resulting in sub 1V dropout. Now I've found that this "low drop out" is in reference to traditional linear regulators (like 78xx series) and what I'm after should probably be called "Ultra Low Drop Out".

author: mariush
author_rank: Super Contributor
timestamp: August 21, 2024, 09:05:37 pm
content: Pay attention when you're picking 1117 regulators.There's versions that are stable with ceramic capacitors on output, like AMS1117 or AZ1117 from Diodes Inc or SPX1117 that are stable with ceramic capacitors and then there's versions which require a minimum ESR on the output, hence why electrolytic capacitors are recommended with those models.For example LM1117 from TI recommends using capacitors with at least 0.3 ohm ESR on output, see page 15 in datasheet :https://www.ti.com/lit/ds/symlink/lm1117.pdfSome versions from ST don't say mention ceramic capacitors, but have a graph "region of stability" where they show minimum 0.1 ohm required or something like that.NCP1117 is only stable with ceramic capacitors if your capacitance is 10uF or higher. See page 5, figure 13:https://www.onsemi.com/pdf/datasheet/ncp1117lp-d.pdfDigikey has loads of filters, just put filter on sot-223 and then sort by voltage drop and you'll get regulators with as little as 50-100mV drop.Here's 377 regulators (sot-223, 800mA to 1.5A output, sorted by dropout voltage) :https://www.digikey.com/short/jb8bb18jFor example you have there AP7361C which has a dropout voltage of 0.36v at 1A..Also, careful with alternatives... 1117 has the tab as Vout , other regulators may have the tab as ground.

author: mtwieg
author_rank: Frequent Contributor
timestamp: August 23, 2024, 01:02:16 pm
content: In practice you shouldn't assume the term "LDO" implies anything about the dropout voltage. "Low" can mean whatever you want it to mean. I treat the term as synonymous with "linear regulator".I would definitely do some basic thermal modelling if you want to push 1A through a SOT223 package though.... in the past I've been surprised by how poorly some SOT223 packages perform. In some cases the same device in a SOT89 package actually had better thermal performance.

author: wraper
author_rank: Unknown
timestamp: August 23, 2024, 01:07:46 pm
content: Quote from: mtwieg on August 23, 2024, 01:02:16 pmCurrent by itself does not mean much, it's all about dissipated power. You can overheat vreg with just 50 mA or run relatively cool at 1A.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 23, 2024, 03:37:35 pm
content: Quote from: mtwieg on August 23, 2024, 01:02:16 pmIt should imply, by definition. Just that the definition is old, but if a regulator with say 30V max input and 2.5V dropout is labeled as "LDO", then it is being mislabeled in error.Quote... which is exactly the error. The fact it's a very common hobbyist error after about 2010 or so, doesn't make it any more right. We can choose to do The Right Thing and stop contributing to the error.

author: TimFox
author_rank: Super Contributor
timestamp: August 23, 2024, 03:44:35 pm
content: History: the original (e.g., 7805) linear voltage regulators used an NPN emitter follower circuit for the pass element (positive regulator), which dominated the dropout voltage due to the BE voltage required.The first LDOs used a PNP pass element, whose saturation voltage (< Vbe) dominated the dropout voltage.Later LDOs used a MOSFET that could operate at even lower voltages.Note that the open-loop output impedance of the original emitter-follower circuit is low, but that of the PNP common-emitter circuit is high: this consideration is important for load capacitance requirements.Applying voltage feedback from the collector of the PNP gives an output impedance that increases with frequency (as the loop gain decreases with frequency), like unto an inductive reactance.All of these circuits work, so long as one respects the characteristics.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 23, 2024, 06:02:16 pm
content: Darlington, even -- hence the 1.5V-ish headroom requirement.Intermediate were parts like LM1117 with the single NPN, and a rather beefy lateral PNP a sizable fraction of the NPN, to push it along:https://upload.wikimedia.org/wikipedia/commons/thumb/e/e4/National_Semiconductor_LM1117_800mA_Linear_Regulator.png/2560px-National_Semiconductor_LM1117_800mA_Linear_Regulator.pngProper open-collector parts soon followed, along with them the picky compensation and awful current limits (wide tolerance, that is). The western-brand ones were pretty good (LM2940 is still pretty good today) and a lot of others stunk.Nowadays, bipolar and CMOS types abound, mostly MOS at low voltages, BJT for wider input range; and most are rated for ceramic capacitors, and better performance in general (tighter current limits, lenient internal compensation, low GND pin current including in dropout, etc.). Still want to check the datasheet carefully -- those two issues in particular, compensation and GND pin current, can be real gotchas when you're not expecting them.Tim

author: ejeffrey
author_rank: Super Contributor
timestamp: August 24, 2024, 11:09:41 pm
content: Quote from: Siwastaja on August 23, 2024, 03:37:35 pmIt's not like it's only or even primarily hobbyists. Many manufacturers and professionals have long since given up the distinction. Conventional dropout ( > 2x Vbe) regulators are archaic, nobody is designing new ones and there are so few left it doesn't make sense to keep a separate category in your catalog. And since "actual" low dropout regulators can have dropout values between 50 mV and 1.2 V it's hardly a useful distinction, you have to look at the dropout curve if you care.It would be better if we just dropped the term LDO altogether and went back to "linear regulator." But by the time the distinction ceased to be meaningful, the majority of active products were labeled LDO, and that's what the majority of engineers looking for new designs were looking for.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 25, 2024, 09:40:30 am
content: Quote from: ejeffrey on August 24, 2024, 11:09:41 pmI agree, and many companies and engineers do exactly that. There are always some who are in such deep love with TLAs that they need their dose of TLA, even if wrong or misleading one. For those, we would need to invent a new TLA such as LVR (Linear Voltage Regulator).Otherwise than that, I agree that a binary classification to "low" and "normal" using an arbitrary limit is not of much help. Today every distributor has parametric search and drop-out voltage is a basic parameter. Any further classification, especially into two separate product pages, only adds confusion.

author: mtwieg
author_rank: Frequent Contributor
timestamp: August 25, 2024, 01:21:54 pm
content: Quote from: Siwastaja on August 23, 2024, 03:37:35 pmAFAIK most manufacturers also use the term LDO to refer to linear regulators in general. For example TI's product browser has the category "Linear & low-dropout (LDO) regulators" which contains all linear regulators (including some with Vdo up to 3V). Within that, you can filter by dropout voltage, but there's no distinction between an "LDO" and a "normal" part.If a product description says "low dropout," you have no right to expect its dropout to be <1V (or whatever you consider low). If an opamp is described as "high bandwidth" I have no right to expect its GBW to be >100MHz. Same for "high efficiency," "low distortion," "low noise," etc.

author: TimFox
author_rank: Super Contributor
timestamp: August 25, 2024, 01:59:15 pm
content: The statement "Linear and low-dropout regulators" does not imply that all linear regulators are low-dropout regulators.

author: mtwieg
author_rank: Frequent Contributor
timestamp: August 25, 2024, 05:25:19 pm
content: Quote from: TimFox on August 25, 2024, 01:59:15 pmI agree. That would require that "low-dropout regulators" actually have a coherent definition (it doesn't, that's my point).If anything, "LDO" should be seen as a marketing term.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 25, 2024, 06:45:29 pm
content: Quote from: mtwieg on August 25, 2024, 01:21:54 pmYou realize you are contradicting yourself? If TI though they are the same thing, then the category title would not look like this.The title is like "fruits and bananas" for a supermarket section - technically correct and making the point that fruits and bananas donotmean the same thing, yet very strange one as one is kind-of a subset of another. "Fruits", or "Linear regulators" would do the job.But TI does it the right way - a single category for all linear regulators, and parametric search for dropout voltage within the category. And then add the magical TLA in the category name for those idiots who otherwise fail to find it. Win-win

author: mtwieg
author_rank: Frequent Contributor
timestamp: August 25, 2024, 11:46:19 pm
content: Quote from: Siwastaja on August 25, 2024, 06:45:29 pmAgain, I'm not saying that they're the same thing, or that TI "thinks" they're the same thing. Just that their search engine treats them like the same thing.QuoteI like this metaphor, but it's not <dadjoke>apples to apples</dadjoke>. At such a supermarket with the "fruits and bananas" section, you'd likely still see a "bananas" section within it. But you don't see an "LDO" subcategory or filter within the "Linear & low-dropout (LDO) regulators" part of TI's search (just a filter for actual dropout voltage, as it should be).A better fruit metaphor would be finding clementines mixed in with the mandarins...Or a better metaphor: what if some moron at International Rectifier decided in the 50s to refer to their Schottky diodes as "Low voltage diodes" (LVD)? Hopefully somebody would have slapped the words out of their mouth. Unfortunately this didn't happen to whoever came up with the term LDO (as opposed to calling them something like "P-Channel linear regulators", which is actually meaningful and coherent).