■ SCREENSHOT 1. Upon power-up, this is the menu
that greets WLAN Phoenix users. This message
bounced through an SP3232 on the WLAN Phoenix to
the SP3243EU on the CP2103 Evaluation Kit board and
out of the CP2103 USB interface to the Tera Term Pro
terminal emulator application running on my laptop.
CP2103 has its own five volt to three volt voltage
regulator. The CP2103's on-chip voltage regulator
allows the CP2103 to use the USB bus power
or be powered by an external power source. In
USBese, powered by an external source is termed
self-powered.
There are three configurations in
which the CP2103's V pin can
DD
participate. In USB Bus-Powered
mode, the V pin is internally
DD
connected to the CP2103's internal
voltage regulator output. The
CP2103's VBUS and REGIN (CP2103
voltage regulator input) pins are both
tied to the incoming VBUS source in
USB Bus-Powered mode. The USB
Bus-Powered configuration enables
the CP2103's voltage regulator
output to be used to power external
circuitry. With 100 mA of available
current capacity, the CP2103's
internal three-volt voltage regulator
can easily power a typical PIC microcontroller. If you examine Schematic
2, you'll see that the CP2103
Evaluation Kit is configured as a USB
Bus-Powered device. The 4. 7 μF
tantalum capacitor hanging on the
V pin is recommended when the
DD
CP2103's internal voltage regulator is
servicing devices in addition to the
CP2103 itself. The additional 0.1 μF
capacitor attached between the
V pin and ground is for noise
DD
suppression. USB Self-Powered mode
is in effect when an external five volt
power source is connected to the
CP2103's REGIN pin. The VBUS
source is also connected to the
VBUS sense input pin and the
internal voltage regulator is enabled,
providing three volts on the V pin
DD
for possible use by supporting
circuitry.
If 3V is applied to the V and
DD
REGIN pins, the internal voltage
regulator is disabled and the CP2103
is considered a USB self-powered
device. The VBUS sense input is fed
by the VBUS source in the configuration, which is defined as USB Self-Powered, Regulator Bypassed mode.
72
February 2009