AT43312A-SC SL383 Atmel, AT43312A-SC SL383 Datasheet - Page 7

• Manufacturer Part Number: AT43312A-SC SL383
• Manufacturer: Atmel

Specifications of AT43312A-SC SL383

• Operating Temperature (max): 70C
• Operating Temperature (min): 0C
• Operating Temperature Classification: Commercial
• Package Type: SOIC
• Mounting: Surface Mount
• Pin Count: 32
• Lead Free Status / RoHS Status: Not Compliant

Power Management
Self-powered Mode
1255G–USB–05/06
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
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 mΩ 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.
ports
AT43312A
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