USB2512 Datasheet, PDF (17/57 Pages) SMSC Corporation – USB 2.0 High-Speed 2-Port Hub Controller

USB251xB/xBi
4.0 BATTERY CHARGING SUPPORT
The USB251xB/xBi hub provides support for battery charging devices on a per port basis in compliance with the USB
Battery Charging Specification, Revision 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 4-1 or by setting the corresponding configu-
ration bits via I²C EEPROM or SMBus (Section 5.1 on page 19).
FIGURE 4-1:
BATTERY CHARGING VIA EXTERNAL POWER SUPPLY
3.3 V
5.0 V
R_STRAP
USB Port Power
Controller
IN
USB251xB/xBi
PRTPWR[x:1]
OCS_N[x]
EN
FLAG
VBUS
Note: R_STRAP enables battery charging.
4.1 USB Battery Charging
A downstream port enabled for battery charging turns on port power as soon as the power on reset and hardware con-
figuration 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.
4.1.1 SPECIAL BEHAVIOR OF PRTPWR PINS
The USB251xB/xBi enables VBUS by asserting the port power (PRTPWR) as soon as the hardware configuration pro-
cess 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 behaviors provide battery charging even when the hub is not enumerated
and protect the hub from sustained short circuit conditions. If the short circuit condition persists when the hub is plugged
into a host system the user is notified that a port has an over-current condition. Otherwise PRTPWR turned on by the
host system and the ports operate normally.
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DS00001692C-page 17