AT43312 View Datasheet(PDF) - Atmel Corporation

Part Name

Description

Manufacturer

AT43312

Self- and Bus Powered USB Hub Controller

Atmel Corporation 

Functional Description

The Atmel AT43312 is a USB hub controller for use in a

standalone hub, as well as an add-on hub for an existing

non-USB peripheral such as a PC display monitor or key-

board. In addition to supporting the standard USB hub

functionality, the AT43312 has additional features to

enhance the user friendliness of the hub.

USB Ports

The AT43312’s downstream ports are standard USB ports.

That is, their functionality complies to the USB specification

and any USB compliant device can be attached to these

ports without any other circuitry or modification. Each port

has a port connectivity status pin.

Dp And Dm Configuration

To match the full-speed cable impedance, 27 Ω series

resistors must be connected between each port’s DM and

DP pins to their corresponding USB connector. In addition,

15 KΩ pull-down resistors are required at each down-

stream port’s DM and DP pins. Port0 is a full-speed port

and requires a 1.5 KΩ pull-up resistor to the 3.3V power

supply. This power supply must be derived from the bus

supplied power.

Port Status Pin

The STATx pins are signals that are not required by the

USB specification. Their function is to allow the hub to pro-

vide feedback to the user whenever a device is properly

connected to the port. A LED and series resistor connected

to STAx can be used to provide a visual feedback.

The default state of STATx is inactive. After a port is

enabled, AT43312 will assert the port’s STATx. Any condi-

tion that causes the port to be disabled inactivates STATx.

Hub Repeater

The Hub Repeater is responsible for port connectivity setup

and tear-down. It also supports exception handling such as

bus fault detection and recovery, and connect/disconnect

detection. Port0 is the root port and is connected to the root

hub or an upstream hub. When a packet is received at

Port0, the AT43312 propagates it to all of the enabled

downstream ports. Conversely, a packet from a down-

stream port is transmitted from Port0.

The AT43312 supports downstream port data signaling at

both 1.5 Mb/s and 12 Mb/s. Devices attached to the down-

stream ports are determined to be either full-speed or low-

speed depending on which data line (DP or DM) is pulled

high. If a port is enumerated as low speed, its output buff-

ers operate at a slew rate of 75-300 ns, and the AT43312

will not propagate any traffic to that port unless it is pref-

aced with a preamble PID. Low-speed data following the

preamble PID is propagated to both low and full-speed

devices. The AT43312 will enable low-speed drivers within

four full-speed bit times of the last bit of a preamble PID,

and will disable them at the end of an EOP. Packets out of

Port0 are always transmitted using the full-speed drivers.

All the AT43312 ports independently drive and monitor

their DP and DM pins so that they are able to detect and

generate the ‘J’, ‘K’, and SE0 bus signaling states. Each

hub port has single-ended and differential receivers on its

DP and DM lines. The ports I/O buffers comply to the volt-

age levels and drive requirements as specified in the USB

Specifications Rev 1.0.

The Hub Repeater implements a frame timer which is timed

by the 12MHz USB clock and gets reset every time a SOF

token is received from the Host.

Serial Interface Engine

The Serial Interface Engine handles the USB communica-

tion protocol. It performs the USB clock/data separation,

the NRZI data encoding/decoding, bit stuffing, CRC gener-

ation and checking, USB packet ID decoding and genera-

tion, and data serialization and de-serialization. The on-

chip phase locked loop generates the high-frequency clock

for the clock/data separation circuit.

Power Management

A hub is a high-powered device and is allowed to draw up

to 500 mA of current from the host or upstream hub. The

AT43312 chip itself and its external hub circuitry consume

less than 100 mA. The AT43312’s power management

logic work with external devices to detect overcurrent and

control power to the ports.

Overcurrent sensing is on a per port basis and is achieved

through the OVCx pins. Each of the OVCx pin is the plus

input of an analog comparator whose other input is con-

nected to a reference voltage source, VREF which is com-

mon to all four ports. Whenever the voltage at OVCx is less

than VREF, the AT43312 treats it as an overcurrent condi-

tion. This could be caused by an overload, or even a short

circuit, and causes the AT43312 to set the port’s

PORT_OVER_CURRENT status bit and its

C_PORT_OVER_CURRENT status change bit. At the

same time, power to the offending port is shut off.

An external device is needed to perform the actual switch-

ing of the ports’ power under control of the AT43312. The

signal to control the external switches are the PWRx pins

which are open drain signals and require external pull-up

resistors of 10 KΩ. Any type of suitable switch or device is

acceptable. However, it should have a low-voltage drop

across it even when the port absorbs full power. In its sim-

plest form, this switch can be a P-channel MOSFET. The

advantages of using a MOSFET switch is its very low volt-

age drop and low cost.

Each one of the AT43312’s port has its own power control

pin which is asserted only when a

Set_Port_Feature[PORT-POWER] request is received

4

AT43312

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