201303.pdf 36567KB Mar 22 2013 09:11:22 PM

2500-mAh Li-ion battery.
The boost-converter IC is located under the shield shown and needs to be close
to its inductor. The function of this IC is to take the battery output voltage and
convert it to 5 or 5.1V to the Mophie USB port through the MOSFETs when it
becomes a host to charge an external device. Its output capability is probably
around 1A. This IC has two sets of five pins on opposing sides. The other two
opposing sides have some sort of heat-sinking pins, which are soldered to the
board, possibly indicating internal power MOSFETs.
USB port.
Power switch.
The USB Li-ion
battery-charger IC
is TI’s bq24040.
It is housed in a
10-pin package
with no shield
(indicating a linear
regulator) and can
handle an ac-walladapter
input or
USB power source
from the micro
USB connector
input. It probably
has integrated
MOSFETs and can
charge at around
1A, meaning the
battery’s maximum
charge time if fully
discharged would
be about three
hours.
Micro USB port.
There are three USB specifications—USB 1.0, 2.0, and 3.0—but here
we focus on USB 2.0, as it’s by far the most common. In any USB network,
there is one host and one device. In this case, the Mophie juice pack is the
host, and your smartphone/tablet/camera is the device. Power always flows
from the host to the device, but data can flow in both directions. In this
case, the USB port is a dedicated charging port.
A USB socket has four pins, and a USB cable has four wires. The inside
pins carry data (D+ and D−); the outside pins provide a 5V power supply.
In terms of actual current (milliamps, or mA), there are three kinds of
USB ports dictated by the current specs: a standard downstream port, a
charging downstream port, and a dedicated charging port. The first two can
be found on your computer (and should be labeled as such); the third kind
applies to “dumb” wall chargers. In the USB 1.0 and 2.0 specs, a standard
downstream port is capable of delivering up to 500 mA (0.5A); in USB 3.0,
it moves up to 900 mA (0.9A). The charging downstream and dedicated
charging ports provide up to 1500 mA (1.5A).
The power MOSFETs are
configured to act as a USBstandard
power switch,
probably also implementing
temperature protection,
short-circuit protection,
and overcurrent protection.
Control is through the USB
port when acting as a host to
charge an external device.
[ www.edn.com ] MARCH 2013 | EDN 27