Description

AN4143

2/9

Doc ID 023460 Rev 1

1

Description

The STG3220 demonstration board is designed for the low-voltage high bandwidth

STG3220 dual SPDT switch. The STG3220 device, in a tiny QFN package, is mounted on

a 4-layer PCB with impedance matched signal tracks. An easily accessible USB connector

on the board allows the board to be used as the USB switch and can be connected to

another USB port (PC host, USB hub, etc.). On the other side of the board there are two

USB receptacles and thanks to the STG3220 device, one of the USB receptacles is active

and connected to the USB port. The active (ON path) is chosen by the manual switch and it

is indicated by the luminous LED diode.

The demonstration board is powered through a USB connector P0, so that it is fully

functional if the P0 is properly connected to the USB port. For the STG3220 device, the USB

VBUS line voltage is decreased to 3.3 V and stabilized by the adjustable and fixed low drop

positive voltage regulator LD1117S33 (component U2).

Table 1.

Main components and connectors

Designator

Description

SW1

USB path selector switch:

USB2 position: P0 - P2 USB path selected, D1 green LED diode is luminous

USB1 position: P0 - P1 USB path selected, D2 green LED diode is luminous

PO

USB connector. Can be connected to USB port (PC, USB hub, etc.)

P1, P2

USB receptacle. USB port for USB device

D3

The yellow LED diode is luminous if the host is in dedicated port charging mode. The

STG3220 device has a built-in dedicated port charging detection circuit to detect the

condition when the USB D+/D- lines are both in high state.

USB2

USB1