AT43312 View Datasheet(PDF) - Atmel Corporation

Part Name

Description

Manufacturer

AT43312

Self- and Bus Powered USB Hub Controller

Atmel Corporation 

AT43312

from the host. PWRx is de-asserted under the following

conditions:

1. Power up

2. Reset and initialization

3. Overcurrent condition

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

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 MΩ or less, under worst case con-

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 VREF, the

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.

3V REG

BUS_POWER

GND

IN

OUT

GND

POWER SUPPLY

5V OUT

GND

VCC5 GND VCC3

R1

VREF AT43312

R2

PWR

MOSFET P

OVC DM DP

DP

DM

PORT_POWER

GND

To

downstream

device

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 MΩ or less under the

worst-case condition.

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.

5

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