at43312 ATMEL Corporation, at43312 Datasheet - Page 5

• Manufacturer Part Number: at43312
• Description: Self- And Bus- Powered Usb Hub Controller
• Manufacturer: ATMEL Corporation

from the host. PWRx is de-asserted under the following
conditions:
Self-powered Mode
In the self-powered mode, power to the downstream ports
must be supplied by an external power supply. This power
supply must be capable of supplying 500 mA per port.
The USB specifications require that the voltage drop at the
power switch, and board traces be no more than 100 mV. A
good conservative maximum drop at the power switch itself
should be no more than 750 mV. Careful design and selec-
Figure 2. Self-Powered Hub Power Supply
Bus-powered Mode
In the bus-powered mode, all the power for the hub itself as
well as the downstream ports are supplied by the root hub
or upstream hub through the USB. Only 100 mA is avail-
able for each of the hub’s downstream devices and there-
fore only low power devices are supported.
The power switch and overcurrent protection work exactly
like the self-powered mode, except that the allowable
switch resistance is higher: 700 M
worst-case condition.
1. Power up
2. Reset and initialization
3. Overcurrent condition
POWER SUPPLY
BUS_POWER
5V OUT
GND
GND
or less under the
R1
R2
MOSFET P
VREF
VCC5
PWR
3V REG
IN
tion of the power switch and PC board layout is required to
meet the specifications. When using a MOSFET switch, its
resistance must be 140 M
ditions. A suitable MOSFET switch for an AT43312 based
hub is a P-channel enhancement mode MOSFET. The
input of the PMOS switch is connected to the local 5V
power supply while the output is connected to the port
power line, as well as the port’s OVCx pin. An overcurrent
condition increases the voltage drop across the MOSFET.
If this voltage drops to less than the voltage at V
AT43312 voltage reference pin, the AT43312 interpretes
this as an overcurrent condition. The AT43312 removes the
power from that port by de-activating the port’s PWRx pin
and reports the condition to the Host.
The diagrams of Figures 2 and 3 show examples of the
power supply and management connections for a typical
AT43312 port in the self-powered mode and bus-powered
mode.
AT43312
OVC
GND
GND
OUT
DM
VCC3
DP
PORT_POWER
GND
DP
DM
or less, under worst case con-
To
downstream
device
REF
, the
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