GL3522-22 Datasheet

© 2014 Genesys Logic, Inc. - All rights reserved.

Page 23

GLI Confidential

CHAPTER 5

BATTERY CHARGING SPECIFICATION REV.1.2

SUPPORT

5.1 Background

The USB ports on personal computers are convenient places for portable devices to draw current for charging

their batteries. This convenience has led to the creation of dedicated chargers that simply expose a USB

standard-A receptacle. This allows portable devices to use the same USB cable to charge from either a PC or

from a dedicated charger.

If a portable device is attached to a USB host or hub, then the USB 2.0 specification requires that after

connecting, a portable device must draw less than:



2.5 mA average if the bus is suspended



100 mA maximum if bus is not suspended and not configured



500 mA maximum if bus is not suspended and configured for 500 mA

If a portable device is attached to a charging host or hub, it is allowed to draw a current up to 1.5A, regardless

of suspend. In order for a portable device to determine how much current it is allowed to draw from an

upstream USB port, the USB-IF Battery Charging specification defines the mechanisms that allow the portable

device to distinguish between a USB standard host, hub or a USB charging host. Since portable devices can be

attached to USB charging ports from various manufactures, it is important that all USB charging ports behave

the same way. This specification also defines the requirements for a USB chargers and charging downstream

ports.

5.2 Standard Downstream Port (SDP)

GL3522-22 complies with Battery Charging Specification rev1.2, which defines three charging ports: SDP,

CDP and DCP. The SDP is a standard USB port which can transfer data and provide maximum 500mA

current.

5.3 Charging Downstream Port (CDP)

GL3522-22 supports battery charging detection, turning its downstream port from a standard downstream port

(SDP) into charging downstream port (CDP). GL3522-22 will make physical layer handshaking when a

portable device that complies with BC rev1.2 attaches to its downstream port. After physical layer

handshaking, a portable device is allowed to draw more current up to 1.5A.

Once the charging downstream port of GL3522-22 is enabled, it will monitor the VDP_SRC on D+ line anytime.

When a portable device, which is compliant with BC rev1.2, is attached to the downstream port, it will drive

VDP_SRC on D+ line to initiate the handshake with charging downstream port. GL3522-22 will response on its

D- line by VDM_SRC and keep in a certain period of time and voltage level. The portable device will accept this

handshaking on its D- line in correct timing period and voltage level, and then turns off its VDP_SRC on D+ line.

GL3522-22 will recognize that charging negotiation is finished by counting time between the portable device

turning on and off its VDP_SRC. After that, the portable device can start to draw more current from VBUS to

charge its battery more rapidly. It can draw current up to 1.5A.

If there is no response from D- line, the portable device will recognize that it is attached to a standard

downstream port, not a charging port.