Usb 2.0 Hub Circuit - NEC MultiSync 20WGX2 Series Service Manual

8. USB 2.0 HUB Circuit

8.1 Block Diagram
(1)
Upperstream port
receptacle
To Host
8.2 Features
. Compliant with Universal Serial Bus specification revision 2.0 (Data rate 1.5/12/480 Mbps).
. 4 (Max.) downstream facing ports.
. Supports self-powered mode only.
. Supports over-current detection.
. Terminal shutdown circuit.
. Over current limiter to prevent system voltage drop.
8.3 Block Description
(1) Host is connected to this USB Hub via USB upperstream cable.
(2) Data traffic protocol between Host and USB devices (downstream ports).
(3) An active low reset output, while +3.3V power on, normal operation going back high state.
(4) A low dropout linear regular which provides stable 3.3V for USB Hub controller.
(5) The block is equipped with an overcurrent detector that is essential for a Host/Hub controller conform-
ing to the USB standard.
(6) USB devices is connected to this USB Hub via USB downstream cable.
8.4 3.3V cutoff circuit for USB identification
I317 is a DC/DC regulator to generate a 3.3V output to USB Hub Controller.
8.5 USB hub control circuit
I319 is a USB hub control IC made by Cypress.
I319 enables communication with upstream port when D+ and D- from the USB connector are applied
to pin 18 and pin 17, respectively. Pin 14, 13, 10, 9, 6, 5, 2 and 1 are connected to the USB connector
of the downstream port. They function as a communication interface between downstream and up-
stream ports. If an overcurrent is generated in the downstream port, it is transferred to the upstream
port.
X302 is a crystal oscillator that supplies a 24MHz clock signal to the USB hub control IC.
8.6 Downstream port circuit
The USB 5V output from the power supply passes through power-switches of I318 and I320, and is led
to the power supply pins (pin 1 and pin 5 of each connector) of the USB Downstream port connector.
An overcurrent signal is given from USB Downstream port through power switch connector line to
detection and overcurrent has been generated in the Downstream port when detected.
(2)
1
/ USB 2.0 HUB controller
Power On Reset 5-3.3V regular
(3) (4)
7- 8
(5)
4 4
/ over current limiter /
(6)
Downstream ports
receptacles
/
To USB devices