Nuts and Volts - February 2009

THE DESIGN CYCLE

Pins 11 and 12 are used for power management. The CP2103's USB function controller supports USB Suspend and Resume signals, and extends the USB power management functionality to external devices via the active high SUSPEND and active low /SUSPEND pins. The CP2103 enters Suspend mode when a suspend signal is active on the bus. An example of how the SUSPEND signals are used can be seen in Schematic 1. Note that the SP3243EU's /SHUTDOWN pin is under the control of the /SUSPEND pin. When the CP2103 goes into Suspend mode, it also shuts down the SP3243EU. The CP2103 exits Suspend mode upon receiving Resume signaling on the bus. A USB Reset signal or a device reset will also terminate Suspend mode.

VBUS, D+, and D- are standard USB signals. The SP0503BAHT attached to these signals is a trio of avalanche transient voltage suppression diodes that are used here for ESD (Electrostatic Discharge) protection.

Driving the CP2103's /RST pin low for more than 15 μs will initiate a CP2103 system reset. The /RST pin is open drain and reflects the status of a CP2103 internal power on reset.

The CP2103's V pin is a power

IO

input pin that determines the voltage level support for the I/O pins.

Voltage at the V pin can vary

IO between 1.8 volts and V . A 0.1 μF DD bypass capacitor is present on the

V pin to suppress noise.

IO

The only remaining components we need to consider in a CP2103 design are shown in Schematic 3. Adding these VBUS bypass capacitors brings the total CP2103 system parts count to seven. It's really sobering to realize that the seeming expanse of the schematics is all contained in the macro view of the CP2103 and its supporting components you see in Photo 3.

ExpressPCB pads and traces for the CP2103 hardware project. Now that we have some idea of what it's going to take to put a CP2103 USB interface together, I'll come up with a CP2103/microcontroller hardware design and have it ready for the next installment of Design Cycle. We'll also take a closer look at USBXpress and use its utilities to customize our CP2103. So, polish up your soldering equipment as you're going to need it.