High-side load switches for USB power rated 5A? - Page 1
Forum section: electronics / projects

author: HwAoRrDk
author_rank: Super Contributor
timestamp: October 02, 2023, 03:27:21 pm
content: I'm wondering if anybody knows of a high-side load switch of the kind typically aimed at switching 5V USB devices that can handle 5A?Currently I have a design that uses a 3A switch like the Diodes AP22815 or Richtek RT9742, but I'm interested in something that can handle higher loads up to 5A. However, I'm having trouble finding anything that fits the bill, and I'm not even sure that something like that exists. By the way, I'm aware that such a thing might not exist, because what kind of USB device even draws that much current? But I'm not actually switching a USB device, just something else that runs on 5V, and USB load switches fit the bill perfectly for my use case.The features I'm primarily interested in are:- Over-current and short-circuit protection- Reverse current/voltage blocking- Fault flag outputMost general-purpose high-side load switches I've found seem to be aimed at automotive use, but aren't suitable as their minimum operating voltages are 5.5-6V, and they don't have reverse blocking.I've found one or two load switches aimed at USB PD (e.g. NXP NX20P5090), but they would be an extreme pain to use, as they have tiny, tiny WLCSP BGA packages.Any suggestions for parts that fit the bill?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 02, 2023, 05:29:45 pm
content: Dumb(?) idea: use two in parallel?Might be load switchcontrollers(external MOSFET), not sure offhand, also probably overkill for the low voltage and simple application.Tim

author: HwAoRrDk
author_rank: Super Contributor
timestamp: October 03, 2023, 11:25:21 am
content: How would that work with the over-current protection? How do you balance the current across the pair?As I understand it, the aforementioned devices that I'm currently using perform OCP by current-limiting when they detect the threshold has been exceeded, which then subsequently triggers thermal protection. But the thresholds are kind of approximate, and not necessarily consistent from individual device to device, so wouldn't that lead to some undesirable behaviour?For example, say I'm using a pair of 2.5A devices, but they have slightly differing RDS(on). The device with the lower on-resistance will take more current, and thus potentially trip too soon because it has too large a share of the current. For example, its share is 2.6A versus 2.4A on the other, so it trips OCP, even though the total current hasn't exceeded 5A.Would I just need to AND the two fault output signals? So that we don't consider an actual fault until both devices have tripped?

author: HwAoRrDk
author_rank: Super Contributor
timestamp: October 03, 2023, 11:52:12 am
content: After a lot more searching, I have actually found a few suitable devices:- Diodes Inc.DPS1135- ON SemiNCP45780- Microchip/MicrelMIC2044/2045It's a bit frustrating trying to find these things, because it varies from manufacturer to manufacturer whether they categorise them under "USB" or "Power Management". I had only been looking at the latter.The DPS1135 looks pretty good - seems like it would do the job, and it's fairly inexpensive (~£1 ea.). It does have a weird 3-sided 0.5mm pitch QFN package, but that's probably manageable. The NCP45780 also looks like a good option, but is twice the price of the DPS1135. Also another unusual QFN package with VIN and VOUT on separate central pads, but workable. The Micrel part, while nice on paper and in an easy-to-use TSSOP package, is stupidly expensive (~£3.50!).I have questions about a couple of features of the DPS1135:What is Fast Role Swap (FRS)? I gather it's part of USB PD, to do with a USB device supporting the ability to either supply power or receive power. It's not clear to me what value I should give the FRS pin for usage where PD isn't involved and I'm just supplying power. Plus the description on page 12 of the datasheet indicates it works off a pulse rather than level?The output discharge control (DISC2) seems to be completely independent of everything else (such that you could even enable it when output is powered!) and not automatic. If I wanted to make it automatic, such that I didn't have to add another MCU GPIO (of which I don't really have any spare) to control it, could I derive control of it from the EN signal so that the output discharge is active whenever EN is off? Maybe invert the EN signal with a small transistor and include a short RC delay?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 03, 2023, 04:24:12 pm
content: Quote from: HwAoRrDk on October 03, 2023, 11:25:21 amWell, so what? If one drops, suddenly there's 5A on the other, it immediately goes into current limiting, it opens thermally a moment (100s us?) later, and both are faulted out. Both stay off until they cool down, which won't track, but this might be as much a feature as a bug: consider it a time-delay 50% foldback. If under MCU control, then reading the fault signals (AND or OR would be acceptable, depending on which characteristic you want; use OR to avoid "undesirable" behavior) and turning them off for a safe margin before turning on again (in which both are expected to be ready again) avoids the "foldback" behavior.Tim

author: Smokey
author_rank: Super Contributor
timestamp: October 04, 2023, 07:55:08 am
content: Digikey parametric search for "Power Distribution Switches, Load Drivers"High Side, Load voltage including 5V, current > 5A, "Fault Protection" = current limit, reverse , and short.https://www.st.com/resource/en/datasheet/stelpd01.pdf*Needs an external fet for reverse current protection, but otherwise least expensive.https://aosmd.com/res/data_sheets/AOZ13984DI-02.pdfhttps://www.ti.com/lit/ds/symlink/tps2559-q1.pdfhttps://www.onsemi.com/download/data-sheet/pdf/ncp45760-d.pdf

author: Psi
author_rank: Super Contributor
timestamp: October 04, 2023, 08:17:23 am
content: Ok, this one looks good.VN5160S-E4.5V min operating supply.4.5V max undervolt shutdown5.4 A current limitReverse battery protection optionHas diag status pin, you can tell if its in overtemp but doesn't look like you can tell if its in current limit. Not sure seems bit odd, i might be reading it wrong.Edit: hm.. digikey says obsolete but ST says its active.

author: Smokey
author_rank: Super Contributor
timestamp: October 04, 2023, 08:20:45 am
content: Quote from: Psi on October 04, 2023, 08:08:09 amHa! you really went for the jugular with that one!4mOhm Ron. That's 0.1W at 5A. Worst case Thermal Rthj-amp = 58.1C/W with a 150C Tj. You would need to be running at an ambient of 144C to trip thermal

author: Psi
author_rank: Super Contributor
timestamp: October 04, 2023, 08:22:34 am
content: Quote from: Smokey on October 04, 2023, 08:20:45 amHehe, i deleted that post once I found that second 5A version that is much more reasonable, but you managed to quote that monster of a switcher before i did.Yeah, its not just overkill but its overkill2We replaced the VN5E010 that went EOL with the VN7004CH in one of our products to PWM the 10A solenoid inside some automotive gearboxes and even that is a very light load for it.

author: Smokey
author_rank: Super Contributor
timestamp: October 04, 2023, 08:25:26 am
content: ST is killing it in this space. They have a whole family of new parts at all power levels. Really reasonable prices considering the capabilities.

author: Psi
author_rank: Super Contributor
timestamp: October 04, 2023, 08:28:17 am
content: Quote from: Smokey on October 04, 2023, 08:25:26 amYeah, they are built like tanks. We've never had a single one fail.And given the price is ok we spec'ed a bigger one than we needed, which might be why, but in any case, they are awesome.

author: HwAoRrDk
author_rank: Super Contributor
timestamp: October 04, 2023, 01:17:20 pm
content: Quote from: Smokey on October 04, 2023, 07:55:08 amHmm, there's one thing I don't like about this one: it has a combined EN/Fault pin. I'm not sure how you're supposed to make that work. Make MCU GPIO an output pulling low to turn off; make a hi-Z input to turn on (so EN is internally pulled high) and upon fault it goes to intermediate voltage which you can read as an input? But the fault VI(INT)is 750-900mV, which is too close to MCU's VILthreshold for my liking. I could maybe use an analog watchdog on the MCU, but that's just complicating things unnecessarily.It's also actually fairly expensive (~£1.50) compared to others, and then plus the cost (monetary and board space) of additional external FET for reverse blocking.Quote from: Smokey on October 04, 2023, 07:55:08 amWas a bit confused by this one, as it says it's intended for currentsinkingapplications, but I guess a load switch is a load switch.Doesn't have any OCP apart from thermal protection. I would prefer explicit OCP/SCP feature, preferably fixed or adjustable at just over 5A (e.g. 5.5-6A). Also only seems to be available at DigiKey. LCSC list it, but don't stock it.Quote from: Smokey on October 04, 2023, 07:55:08 amNice, like it.A little pricey, though.Quote from: Smokey on October 04, 2023, 07:55:08 amA variant on what I already found (the NCP45780). But weirdly the '760 is rated for 8A but has ahigherRDS(on)than the '780 rated for 7A (20mΩ vs. 13.5 mΩ).

author: HwAoRrDk
author_rank: Super Contributor
timestamp: October 04, 2023, 01:28:11 pm
content: Quote from: Psi on October 04, 2023, 08:17:23 amlolwut? 210mΩ RDS(on)when operating at 5V?!? That would be dissipating over 5W at 5A!How does it do current limiting to 5.4A? By catching fire?Quote from: Psi on October 04, 2023, 08:17:23 amIsn't that reverse polarity protection rather than reverse current blocking? (i.e. prevent the output back-powering the input)

author: Psi
author_rank: Super Contributor
timestamp: October 04, 2023, 08:37:02 pm
content: Quote from: HwAoRrDk on October 04, 2023, 01:28:11 pmTrue, i missed that bit.But its a moot point since they carry them in all sizes.Here's the same thing but 40mR, so 1W @ 5Ahttps://www.st.com/resource/en/datasheet/vn5025aj-e.pdfQuote from: HwAoRrDk on October 04, 2023, 01:28:11 pmwell it stops the chip exploding, so im guessing that is what OP wanted.

author: Smokey
author_rank: Super Contributor
timestamp: October 05, 2023, 02:56:39 am
content: Quote from: HwAoRrDk on October 04, 2023, 01:17:20 pmNot sure why they word it like that. Go to page 5 of the datasheet. The internal schematic is just a high side switch with reverse protection (back to back fets).

author: HwAoRrDk
author_rank: Super Contributor
timestamp: October 10, 2023, 10:02:26 am
content: I think that I'm going to go with the TITPS2557. It's basically the same as the TPS2559, but it actually supports a proper 5A, rather than the 4.7A of the '2559. It's also pretty cheap. (I don't understand the deal with the '2559's ratings. Front page blurb says 5.5A, but feature bullet points state 4.7A and minimum ILIM resistor value gives 4.7A - I don't know where they get the 5.5A from unless you ignore the recommended operating conditions.)But I want to confirm one thing: the TPS2557 does actually have reverse current blocking,right?It doesn't explicitly say so anywhere on the datasheet, but if we compare with the TPS2559 which does, they both illustrate the functional block diagram as having a switching MOSFET configured with the bulk/body connected to ground:From what I gather from other datasheets of similar devices, this means that effectively the FET has no body diode, and therefore won't conduct in any direction when off.

author: Psi
author_rank: Super Contributor
timestamp: October 10, 2023, 10:48:35 am
content: Quote from: HwAoRrDk on October 10, 2023, 10:02:26 amI wouldn't recommend making any assumptions about the body diode just looking at those symbols.It has to have a body diode, no way around that.But it might actually be two fets in series with opposite polarity, or it might just be a normal fet with normal body diode and they just used an oddball symbol.The datasheet should mention if its 'special' and will block in both direction.If it doesnt mention anything, then assume its a single fet with normal body diode.

author: HwAoRrDk
author_rank: Super Contributor
timestamp: October 10, 2023, 01:53:24 pm
content: I found an answer on the TI E2E forum:https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/789894/tps2557-tps2557https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/476523/tps2557-reverse-input-output-voltage-conditionYes, it does have reverse current protection. The output can't back-feed the input. However, it does not feature reverse voltage protection against output voltage higher than input while the switch is on.Edit:In fact, I have just realised that there is actually a clue in the datasheet. In the power switch characteristics, it defines IREVreverse leakage current as being maximum of 1 uA, but if you look at the conditions for that, it states they are VOUT= 6.5 V, VIN= 0 V - i.e. when the output voltage is powered but the device is unpowered.

author: langwadt
author_rank: Super Contributor
timestamp: October 10, 2023, 03:32:42 pm
content: Quote from: HwAoRrDk on October 10, 2023, 01:53:24 pmor the abs max Vin-Vout = +/-7V