Google-branded phones and wireless chargers that deliver peak recharge speeds only when they're used together.
Within my late-March 2019 status-update piece on wireless charging, which was published shortly after a single-coil Q1 charger teardown and ahead of the subsequent dissection of a dual-coil unit, I wrote:
Google added native (versus clumsy accessory-supplemented) wireless charging to the Pixel 3 smartphone family in late 2018. That last one’s the source of a “gotcha” qualifier…unlicensed third-party chargers are restricted to 5W capabilities. Even now, six months later, your only option for 10W charging on Pixel 3s is Google’s own $79 Pixel Stand (due to concerns about compatibility? Profitability? Both? You decide.).
Ever since, I’ve been hankering to get inside one and try to figure out how it does its differentiation tricks. In retrospect, my sole-sourced statement wasn’t exactly accurate, although in effect I was still spot-on. As the 9 to 5 Google writeup I’d linked to earlier noted, Belkin had also announced both pad and stand variants of a “Boost Up” charger that supplied Pixel phones with 10W charging capabilities (along with 5W support for standard phones):
They’re no longer available (I’m linking to Amazon product pages here because the corresponding pages on Belkin’s site no longer exist) and my sense is that they didn’t ever ship in high volumes. Ironically, the product page for the first-generation Pixel Stand also no longer exists on Google’s site; it auto-forwards to the page for the newly-released (but not yet shipping as I write this) second-generation Pixel Stand, which supplies up-to-23W charging capabilities to the latest Pixel 6 series phones, along with up-to-15W support for other EPP-capable phones:
Here’s the Amazon page for the first-generation Pixel Stand as an alternative info source.
Speaking of compatibility, what’s with the “(some)” qualifier in this write-up’s title? The first-generation Pixel Stand was introduced alongside the Pixel 3 and larger Pixel 3 XL, the first Google phones that included wireless charging support (the links go to iFixit’s teardowns of both phones, so you can see what the charger’s circuitry inductively mates with). That said, it also supports the successor Pixel 4 and Pixel 5 at higher-than-5W charging speeds. It does not, however, support the “A” Pixel variants, which tend to be the primary phones I use, and which (among other things) omit wireless charging support as a cost-savings move.
Enough overview; let’s get to tearing down! I’ll as-usual begin with some overview shots (I bought this particular unit off eBay; the stand itself is unused but the original owner retained the 1.5m USB-C cable and 18W USB PD power adapter for wired-charging use with a phone):
Behold our patient:
Note the (remove before using) protective plastic film over the charge plate. Below is a standalone shot of the stand (with the plastic film removed) along with the as-usual 0.75″ (19.1 mm) diameter U.S. penny for size comparison purposes (the Pixel Stand, per the Amazon product page, has dimensions of 4.1 x 3.6 x 4.1 inches and weighs 5.6 ounces):
And now with one of my Pixel 3a phones (which again don’t support wireless charging…think conceptual here, folks) mounted on it:
Remove the phone, flip the Pixel Stand upside down and…more protective plastic!
Removing it gives a clear view of the USB-C port:
Also stamped on the bottom (among other things), by the way, is the FCC ID: 2APYSG019C. For what it’s worth, the certification documentation identifies the unit as a “Lanto Electronic Ltd Wireless Charger.”
Time to dive inside, beginning with the bottom, which ended up being easier to remove than I’d feared. Unlike this Neanderthal, I chose a civilized small flat-head screwdriver, not a hunting knife:
Unsnap a few tabs, pull away some glue, and:
Not much to see yet, though those two Faraday cages (or heat sinks? Or both?) are intriguing:
At this point, I redirected my attention to the charging pad, which again came apart fairly easily…at least to a point:
It stubbornly refused to completely detach from the base; that is until I revisited the base, removed two screws from the center and snipped some wires:
The inside of the front cover (bottom) is nothing to write home about, but the back half (top) is much more interesting. It’s conceptually reminiscent of the two-coil layout of the Seneo unit whose teardown EDN published in December 2019, complete with both “portrait” (top) and “landscape” (bottom) coil orientations (optimized for both possible device orientations when placed on the stand; by the way, did you also notice the nifty ridge built into the charger that keeps the device from slipping off?). But it adds a square-shaped sensor (or something) in the middle of each coil:
I’m guessing they’re for temperature monitoring purposes, to prevent overheating. Readers?
The back of the metal (versus flimsy plastic with the Seneo) plate that holds the two-coil assembly together is stubbornly sticky-taped to the plastic half-chassis behind it:
And with that, let’s return our attention to the PCB in the base. Initial disassembly steps were straightforward, once I removed four more screws and peeled the metal plate away from the plastic top chassis piece:
At this point, I was initially stumped; the two metal “lobes” (for lack of a better word) were firmly attached to the PCB and resisted all initial attempts to pry them away with a flat head screwdriver. So I temporarily turned my attention to the junction between the PCB and the metal plate behind it, which was much more amenable to my coaxing:
Here’s a close-up of the translucent lens that focuses and redirects to the outside world the output of the PCB-located LED:
Speaking of which…back to the PCB front side. Did you already notice the seven holes: four in one “lobe,” three in the “other?”
Well, I tried jamming one tip of a precision tweezer set in one of them and using it to lift the “lobe” off, which only resulted in me bending the tweezer tip. A heat gun didn’t do the trick, either, although via its application I learned that the PCB backside included several pieces of adhesive protective tape:
However, I’m happy to report that one final application of the flat head screwdriver, with a bit more muscle (and colorful accompanying language) and also leveraging the USB-C connector as a fulcrum, was ultimately successful:
Voila. Note first and foremost the aforementioned LED at the bottom of the PCB.
Let’s peer closer:
In the bottom left quadrant of the photo are two landscape-dominant ICs: an IDT (now Renesas) P9242-R wireless power transmitter “for 15W applications” (I’m quoting the datasheet) and a Winbond 25X40CLNIG 4 Mbit serial flash memory. There are two identically-labeled devices in the upper right quadrant:
Along with them is a mysterious (at least to me) STMicroelectronics STM32 microcontroller (you may recall that I was unable to definitively identify the STMicro µC in the Seneo teardown, either). Again…readers?
I admittedly exit this project still a bit frustrated, because I wasn’t able to sort out exactly how the Pixel Stand knows that it’s got a Pixel phone sitting on it (versus a conventional Qi-supportive device) and accordingly boosts its charging power. Within this Reddit mini-teardown and discussion thread is a post that postulated “the ability to draw 10W is triggered by the data stream embedded in the Qi transmission.”
I’m not aware of any specific over-the-air handshake like this that occurs between the wireless transmitter and receiver, but then again I’m admittedly not intimately familiar with the Qi specifications, either. All I’ve been able to ascertain from the Qi entry in Wikipedia is this:
Regulation of the output voltage is provided by a digital control loop where the power receiver communicates with the power transmitter and requests more or less power. Communication is unidirectional from the power receiver to the power transmitter via backscatter modulation. In backscatter modulation, the power-receiver coil is loaded, changing the current draw at the power transmitter. These current changes are monitored and demodulated into the information required for the two devices to work together.
Feedback in the comments from knowledgeable readers on this or anything else I’ve introduced (or overlook) is as-always welcomed!
This article was originally published on EDN.
Brian Dipert is Editor-in-Chief of the Edge AI and Vision Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the company’s online newsletter.