USB2422

DS00001726B-page 14

3.0

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 Figure 3-1 or by setting the corresponding config-

uration bits via SMBus (Section 4.1 on page 16).

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 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.

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 pro-

cess 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.

FIGURE 3-1:

BATTERY CHARGING VIA EXTERNAL POWER SUPPLY

Note:

USB2422

USB Port Power

Controller

IN

EN

FLAG

VBUS

5.0 V

3.3 V

PRTPWR1

OCSx_N