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AT43312A-SC

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27
7
AT43312A
1255F–USB–3/04
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 AT43312A chip itself and its external hub circuitry consume
much less than 100 mA. The AT43312A’s power management logic works 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.
Whenever the voltage at OVCx
is asserted, the AT43312A treats it as an overcurrent
condition. This could be caused by an overload, or even a short circuit and could cause
the AT43312A 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 offend-
ing port is shut off and its STATx
generates a square wave with a frequency of about 1
second.
An external device is needed to monitor the overcurrent condition and perform the
actual switching of the ports’ power under control of the AT43312A. 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 simplest form this switch can be a P-chan-
nel MOSFET. One advantage of using a MOSFET switch is its very low-voltage drop
and low-cost.
Each one of the AT43312A’s port has its own power control pin which is asserted only
when a SetPortFeature[PORT-POWER] request is received from the host. PWRx
is de-
asserted under the following conditions:
1. Power-up
2. Reset and initialization
3. Overcurrent condition
4. Requested by the host through a ClearPortFeature [PORT_POWER] for ALL the
ports
Self-powered Mode In the self-powered mode, power to the downstream ports must be supplied by an exter-
nal power supply. This power supply must be capable of supplying 500 mA per port for a
total of 2A.
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 75 mV. Careful design and selection of the power
switch and PC board layout is required to meet the specifications. When using a MOS-
FET switch, its resistance must be 140 m
Ω or less under worst case conditions. A
suitable MOSFET switch for an AT43312A based hub is an integrated high side dual
MOSFET switch such as the Micrel MIC2526.
8
AT43312A
1255F–USB–3/04
Bus Powered Mode In the bus powered mode, all the power for the hub itself as well as the downstream
ports is supplied by the root hub or upstream hub through the USB. Only 100 mA is
available for each of the hub’s downstream devices and therefore only low power
devices are supported.
The power switch and overcurrent protection works exactly like the self-powered mode,
except that the allowable switch resistance is higher: 700 m
Ω or less under the worst
case condition.
The diagrams of Figure 2 and Figure 3 show examples of the power supply and man-
agement connections for a typical AT43312A port in the self-powered mode and bus
powered mode.
Figure 2. Self-powered Hub Power Supply
GND
POWER SUPPLY
PORT_POWER
5V OUTPUT
GND
SWITCH
IN OUT
FLG
CTL
To
Downstream
Device
GND
VCC
AT43312A
PWR
OVC
LPSTAT
U2
U1
PS5
BUS_POWER
GND
R1
47K
9
AT43312A
1255F–USB–3/04
Figure 3. Bus Powered Hub Power Supply
Port Status Pin The STATx
pins are signals that is not required by the USB specification. Its function is
to allow the hub to provide feedback to the user whenever a device is properly con-
nected to the port. An LED and series resistor connected to STATx
can be used to
provide a visual feedback. If an overcurrent condition is detected at a port, the STATx
of
the offending port will alternately turn on and off causing an LED to blink. The LED will
continue to blink until power to the offending port is turned off by the host or until the hub
is re-enumerated.
The default state of STATx
is inactive. After a port is enabled AT43312A will assert the
port’s STATx
. Any condition that causes the port to be disabled inactivates STATx.
Note: The I/O Pins of the AT43312A should not be directly connected to voltages less than
VSS or more than the voltage at the CEXT pins. If it is necessary to violate this rule,
insert a series resistor between the I/O pin and the source of the external signal source
that limits the current into the I/O pin to less than 2 mA. Under no circumstances should
the external voltage exceed 5.5V. To do so will put the chip under excessive stress.
Hub Controller The Hub Controller of the AT43312A provides the mechanism for the Host to enumerate
the Hub and the AT43312A to provide the Host with its configuration information. It also
provides a mechanism for the Host to monitor and control the downstream ports. Power
is applied, on a per port basis, by the Hub Controller upon receiving a command, Set-
PortFeature[PORT_POWER], from the Host. The AT43312A must be configured first by
the Host before the Hub Controller can apply power to external devices.
The Hub Controller contains two endpoints, Endpoint0 and Endpoint1 and maintains a
status register, Controller Status Register, which reflects the AT43312A’s current set-
tings. At power up, all bits in this register will be set to 0’s.
GND
PORT POWER
SWITCH
IN OUT
FLG
CTL
To
Downstream
Device
GND
VCC
AT43312A
PWR
OVC
LPSTAT
U2
U1
BUS_POWER
GND
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27

AT43312A-SC

Mfr. #:
Buy AT43312A-SC
Manufacturer:
Microchip Technology / Atmel
Description:
USB Interface IC FULL FEATURED USB HUB CONTROLLER
Lifecycle:
New from this manufacturer.
Delivery:
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