How can a simple USB cable fry your device?

Hint: When its maker doesn’t know what it’s doing.

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Hint: When its maker doesn’t know what it’s doing.

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“A do-it-all standard designed to accommodate past, current, and future devices, it’s only a matter of time before USB-C becomes a universal standard.”

It wasn’t that long ago when a 5-volt/1-amp charger was good enough to charge most smartphones.

But as screen sizes keep growing, SoCs get more powerful, datahungry apps become commonplace, and (as a result) batteries get bigger, good luck waiting for modern smartphones to recharge if you continue to use these 5-watt chargers.

Which is why many phone and SoC makers have taken matters into their own hands. In addition to the common Battery Charging v1.2 spec from the USB Implementers Forum, which is the non-profit organization behind the USB standard, we also see plenty of proprietary fast-charging methods out there in the market, such as Apple’s 2.4A discovery scheme, Qualcomm’s Quick Charge, Huawei/HiSilicon’s Fast Charging Protocol, and Oppo’s VOOC, just to name a few.

One that’s gaining a lot of attention lately is USB-C, which beyond its user-friendly reversible connector, is able to power 5V devices with up to 3A of current. On compatible high-power devices such as today’s smartphones, this mode will allow them to charge up faster.

There’s also something else called USB Power Delivery, which increases power transfers even further for more powerful devices (see box story).

A do-it-all standard designed to accommodate past, current, and future devices, it’s only a matter of time before USB-C becomes a universal standard. This explains why you’ve been seeing more and more USB-C-based products, big and small, popping up in the last 12 months - from Google’s Pixel and Samsung’s Galaxy S8 phones to Nintendo’s Switch gaming console, Apple’s MacBook Pros laptops and LG’s UltraFine monitors.

New standard, new teething issues Now, most people don’t (and shouldn’t) care about how USB works or the nuances of USB charging. If your phone has a USB Type-C port and your laptop has a regular USB.

Type-A port, to connect the two, all you need is a simple USB-Type-CtoA cable, right? I mean, it’s just a cable with two different plugs, what can go wrong?

Turns out, things can indeed go wrong, especially when power is involved. Not so long ago, there was this story about Benson Leung, a Google engineer, who fried his Chromebook Pixel laptop after using a third-party USB-C-to-A cable.

Dieter Bohn, who is executive editor at The Verge, also ended up with a MacBook Air with no working USB ports after he used a cheap USB-CtoA cable to charge his Nexus 6P phone. And more recently, Russell Holly, contributing editor at Android Central, discovered that his USB-Cbased phone had run out of juice even when connected to a power bank overnight, because the phone decided to charge the power bank instead.

Seriously, we’ve been using USB to connect or charge our devices since forever. Why should USB-C be any different?

It’s complicated In the future, all our devices will be using USB-C, and the only cable we’ve to deal with is a USB-C-to-C cable. But until that day arrives, to hook up our existing devices stuck with legacy ports with new purchases that use USB-C, we’ve to rely on things like USB-A-to-C or microBtoC adapters and cables.

And herein lies the problem: many cables with a USB-C plug on one end and a legacy plug on the other end are not properly built.

You see, as simple as they may look, USB cables have plenty of engineering smarts in them. They all have resistors that, for ease of explaining, relay information about the power source’s capability to the device that’s drawing power. In the aforementioned cases of electronics failing, the culprit was always the USB-C-to-A cable. In Benson Leung’s case, he got a completely miswired cable. For Dieter Bohn, his cable packed a wrong 10kΩ pull-up resistor (when it should have been 56kΩ), so his laptop’s USB port blew when the phone tried to pull too much power than what the port was capable of.

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Who’s to blame?

When such incidents happened, it’s human nature to point fingers. Did the USB-IF do a poor job defining the USB-C spec? Did the cable makers cut any corners? Was the user at fault for not doing enough research before buying?

Unfortunately, the answer isn’t that straightforward. But one thing’s for sure, this isn’t your typical “user problem”. To rehash, when I’ve a phone that uses USB-C but my laptop or charger only has full-size USB-A ports, it’s natural for me to assume that any USB-C-to-A cable that I find in stores (or the one that came with my new phone) will do the job connecting the two. This is expected user behavior.

At the same time, it’s not hard to see where accessory makers can trip up in this whole USB-C affair. The 10kΩ or 3A pull-up resistor found in out-of-spec USB-C-to-A cables is most likely put in to “ensure” that the cable can deliver a 3A current at 5V; but that’s a schoolboy’s mistake because this resistor will also (wrongly) tell the USB-C device that it can draw 3A from the power source. The USB-C device will simply follow this instruction and literally suck the life out of the PC’s or charger’s USB-A port.

You might be wondering, “Don’t all PCs have mechanisms to detect such abnormal behaviors and prevent damage?” Yes, most major laptop and motherboard makers do offer some kind of over current/overvoltage and short circuit protections on their products, but it’s hard to know their limits. (And you shouldn’t test them.) Say a laptop may have time to shut down its 1A port when it senses something is trying to draw 3A from it, but can it react fast enough if it jumps to 5A?

Picking the right cable If there’s anything good that came out of these reports, it’d be that consumers are now paying more attention to the new USB-C standard and the gadgets they buy, even for accessories as simple as cables. If you’re shopping for a USB-C cable with a legacy plug on one end, the least you can do is to stay away from cheap, unboxed, and/or unlabeled ones often found in “discount” bins in some stores.

Looking for USB-IF-certified logos on the packaging or the cable/ connector overmold is another way to identify a properly-built USB-C cable or adapter, but sadly, that alone isn’t foolproof. For one, there are many cables that are properly built but don’t carry those markings because their makers can’t be bothered to apply for the certification. Secondly, like Apple’s MFi (Made for iPhone/iPod/iPad) logo, there are way too many fiybynight manufacturers that use USB-IF’s logos on their untested products. If anything, I’d trust a cable which packaging says it uses a 56kΩ resistor, because to me, that’s the cable maker telling me that it knows its stuff.

Google engineer Benson Leung (yes, the same one) has also taken upon himself to review USB-C accessories on Amazon in his free time.

It’s a list I always check before I buy a new USB-C cable or charger.

It may sound strange, but the truth is everyone - be it manufacturers or consumers - is still learning about USB-C. Device and accessory makers are learning fast, but since there are way too many of them, we can’t expect all of them to get their act together overnight. Ultimately, we’re responsible for our own (and our devices’) safety.