HWM Singapore — May 2017

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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
ï nd 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
10kš 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/over-

voltage 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?

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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-certiï ed

logos on the packaging or the cable/

connector overmold is another

Mode:

USB

2.0

Nominal Voltage:

5V

Current:

Up to

0.5A

Mode:

USB

3.1

Nominal Voltage:

5V

Current:

Up to

0.9A

Mode:

USB with

BC v1.2

Nominal Voltage:

5V

Current:

Up to

1.5A

Mode:

USB-C

at 1.5A

Nominal Voltage:

5V

Current:

1.5A

Mode:

USB-C

at 3A

Nominal Voltage:

5V

Current:

3A

Mode:

USB-

PD

Nominal Voltage:

Up to 20V

Current:

Up to

5A

86 +:0 | MAY 2017