Smsc LAN9512 User Manual download pdf (Page 16)

USB Hub with Integrated 10/100 Ethernet Controller

Datasheet

Revision 1.0 (04-20-09) 16 SMSC LAN9512

DATASHEET

2.1 Port Power Control

This section details the usage of the port power control pins PRTCTL[3:2].

2.1.1 Port Power Control Using a USB Power Switch

The LAN9512 has a single port power control and over-current sense signal for each downstream port.

When disabling port power the driver will actively drive a ‘0’. To avoid unnecessary power dissipation,

the internal pull-up resistor will be disabled at that time. When port power is enabled, the output driver

is disabled and the pull-up resistor is enabled, creating an open drain output. If there is an over-current

situation, the USB Power Switch will assert the open drain OCS signal. The schmitt trigger input will

recognize this situation as a low. The open drain output does not interfere. The overcurrent sense filter

handles the transient conditions, such as low voltage, while the device is powering up.

Figure 2.2 Port Power Control with USB Power Switch

USB Power

Switch

OCS

USB

Device

LAN9512

PRTCTL3

USB Power

Switch

OCS

USB

Device

PRTCTL2

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Smsc LAN9512 User Manual Page 16