Usb Circuit; Outline; Usb Downstream Power Supply; Hub Controller Power Output - NEC FP1355 Service Manual

1.10 USB circuit

1.10.1 Outline

This monitor loads the standard USB SELF POWERED HUB with 1 upstream and 3
downstreams.
(1) Serial data bus
Data bus is connected from upstream connector J1A0 to upstream port of HUB controller
IC1A0, and downstream connector J1A1 and J1A2 are connected from HUB controller.
HUB controller relays data communication between the upstream side (PC) and the down-
stream side (device).
Port on circuit diagram
port 1
port 2
port 3
(2) Power supply to downstream
USB HUB of this monitor is SELF POWERED HUB, and it can supply the power of +5V
500mA (max) to each downstream from transformer T902 on PWB-MAIN. Further, HUB
controller IC1A0 has the function of detecting overcurrent, and stops supplying the power
to each downstream port when overcurrent (500mA or more) is detected at each port.

1.10.2 USB downstream power supply

(1) Supply of Vpp power
When HUB controller IC1A0 is recognized from the direction of upstream, the signal which
functions as a switch of power output for a downstream port is output (IC1A0 #2, 16, 32).
When IC1A0 #2, 16 and 32 become LOW, FET gates are turned ON, and EFT transistors
Q1A1, Q1A2 and Q1A3 supply the power to the downstream ports (J1A1 #1, #5, J1A2 #1)
respectively.
(2) Detection of overcurrent
HUB controller IC1A0 has the function of detecting ovecurrent. If the current output at each
port exceeds 550mA (min), gates of FET transistors Q1A1, Q1A2 and Q1A3 turn OFF
(HIGH), automatically output of current stops only to the port that overcurrent is detected.
In order to re-operate the port that overcurrent is detected, either of the followings should
be carried out:
1. OFF/ON of monitor power supply
2. Pulling-out and pulling-in of upstream cable
3. Restart of PC

1.10.3 HUB controller power output

HUB controller IC1A0 has a built-in 3.3V regulator, and outputs from IC1A0 #1.
Downstream connection of HUB controller
Connector
J1A1
J1A2 (UP)
J1A2 (DOWN)
1 - 58
Silk indication
3
1
2