USB 2.0 Hi-Speed Hub Controller

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Chapter 7 Battery Charging Support

7.1General Description

The battery charging feature is only available in USB251xB (which represents USB2512B/3B/4B and USB2512Bi/3Bi/4Bi hub family products). Any one or combination of downstream ports on the USB251xB hub can be configured to support battery charging.

The SMSC hub provides support for battery charging devices on a per port basis in compliance with the USB Battery Charging specification, version 1.1. The hub can be configured to individually enable each downstream port for battery charging support either via pin strapping as illustrated in Figure 7.1 or by setting the corresponding configuration bits via EEPROM or SMBus.

 

3.3 V

5 V

 

 

USB Port Power

 

RSTRAP

Controller

 

 

IN

USB251xB/xBi

PRTPWR[x]VBUS

 

EN

 

OCS_N[x]FLAG

 

 

Note: RSTRAP enables battery charging.Figure 7.1 Battery Charging via External Power Supply
7.2USB Battery Charging

A downstream port enabled for battery charging turns on port power as soon as the configuration process has completed. The hub does not need to be enumerated nor does VBUS_DET need to be asserted for the port power to be enabled. These conditions allow battery charging in S3, S4 and S5 system power states as well as in the fully operational state. The USB Battery Charging specification does not interfere with standard USB operation, which allows a device to perform battery charging at any time.

A port that supports battery charging must be able to support 1.5 amps of current on VBUS. Standard USB port power controllers typically only allow for 0.8 amps of current before detecting an over-current condition. Therefore, the 5 volt power supply, port power controller or over-current protection devices must be chosen to handle the larger current demand compared to standard USB hub designs.

7.2.1Special Behavior of PRTPWR Pins

The SMSC hub enables VBUS by asserting the port power (PRTPWR) pin as soon as the hardware configuration process has completed. If the port detects an over-current condition, PRTPWR will be turned off to protect the circuitry from overloading. If an over-current condition is detected when the hub is not enumerated, PRTPWR can only be turned on from the host or if RESET_N is toggled. These

SMSC USB251x

31

Revision 1.0 (3-11-09)

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