2-Port USB 2.0 Hi-Speed Hub Controller
Datasheet
DS00001726A-page 18
2014 Microchip Technology Inc.
Chapter 3 Battery Charging Support
The USB2422 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 (Port 1 only) as
illustrated in
or by setting the corresponding configuration bits via SMBus (
Figure 3.1 Battery Charging via External Power Supply
Note:
R
STRAP
enables battery charging.
3.1
USB Battery Charging
A downstream port enabled for battery charging turns on port power as soon as the power on reset
and hardware 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.
3.1.1
Special Behavior of PRTPWR Pins
The USB2422 enables VBUS by asserting the port power (
PRTPWR[2:1]
) as soon as the hardware
configuration process has completed. If the port detects an over-current condition,
PRTPWR[2:1]
will
be turned off to protect the circuitry from overloading. If an over-current condition is detected when the
hub is not enumerated,
PRTPWR[2:1]
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[2:1]
turned on by the host system and the ports operate normally.
USB2422
USB Port Power
Controller
IN
EN
FLAG
VBUS
5.0 V
3.3 V
R
STRAP
PRTPWR1
OCS
x
_N