USB 2.0 Hi-Speed Hub Controller
Datasheet
Chapter 7 Battery Charging Support
7.1
General 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
or by setting the corresponding configuration bits via EEPROM or SMBus.
3.3 V
5V
R
STRAP
USB Port Power
Controller
IN
USB251xB/xBi
PRTPWR[x]
OCS_N[x]
EN
FLAG
VBUS
Note:
R
STRAP
enables battery charging.
Figure 7.1 Battery Charging via External Power Supply
7.2
USB 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.
7.2.1
Special 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)
DATASHEET
SMSC [ SMSC CORPORATION ]
