TPS2511

www.ti.com

SLUSB18 – JUNE 2012

DETAILED DESCRIPTION

Overview

The following overview references various industry standards. It is always recommended to consult the latest

standard to ensure the most recent and accurate information.

Rechargeable portable equipment requires an external power source to charge its batteries. USB ports are

convenient locations for charging because of an available 5-V power source. Universally accepted standards are

required to ensure host and client-side devices meet the power management requirements. Traditionally, USB

host ports following the USB 2.0 Specification must provide at least 500 mA to downstream client-side devices.

Because multiple USB devices can be attached to a single USB port through a bus-powered hub, it is the

responsibility of the client-side device to negotiate the power allotment from the host to guarantee the total

current draw does not exceed 500 mA. The TPS2511 provides 100 mA of current to each USB device. Each

USB device can subsequently request more current, which is granted in steps of 100 mA up 500 mA total.. The

host may grant or deny the request based on the available current.

Additionally, the success of the USB technology makes the micro-USB connector a popular choice for wall

adapter cables. This allows a portable device to charge from both a wall adapter and USB port with only one

connector.

One common difficulty has resulted from this. As USB charging has gained popularity, the 500-mA minimum

defined by the USB 2.0 Specification or 900 mA defined in the USB 3.0 Specification, has become insufficient for

many handsets, tablets and personal media players (PMP) which have a higher rated charging current. Wall

adapters and car chargers can provide much more current than 500 mA or 900 mA to fast charge portable

devices. Several new standards have been introduced defining protocol handshaking methods that allow host

and client devices to acknowledge and draw additional current beyond the 500 mA (defined in the USB 2.0

Specification) or 900 mA (defined in the USB 3.0 Specification) minimum while using a single micro-USB input

connector.

The TPS2511 supports three of the most common protocols:

•

USB Battery Charging Specification, Revision 1.2 (BC1.2)

•

Chinese Telecommunications Industry Standard YD/T 1591-2009

•

Divider Mode

In these protocols there are three types of charging ports defined to provide different charging current to client-

side devices. These charging ports are defined as:

•

Standard downstream port (SDP)

•

Charging downstream port (CDP)

•

Dedicated charging port (DCP)

The BC1.2 Specification defines a charging port as a downstream facing USB port that provides power for

charging portable equipment.

Table 1 shows different port operating modes according to the BC1.2 Specification.

Table 1. Operating Modes Table

MAXIMUM ALLOWABLE CURRENT

SUPPORTS USB 2.0

DRAWN

PORT TYPE

COMMUNICATION

BY PORTABLE EQUIPMENT (A)

SDP (USB 2.0)

Yes

0.5

SDP (USB 3.0)

Yes

0.9

CDP

Yes

1.5

DCP

No

1.5

The BC1.2 Specification defines the protocol necessary to allow portable equipment to determine what type of

port it is connected to so that it can allot its maximum allowable current drawn. The hand-shaking process is two

steps. During step one, the primary detection, the portable equipment outputs a nominal 0.6 V output on its D+

line and reads the voltage input on its D- line. The portable device concludes it is connected to a SDP if the

voltage is less than the nominal data detect voltage of 0.3 V. The portable device concludes that it is connected

to a Charging Port if the D- voltage is greater than the nominal data detect voltage of 0.3V and less than 0.8 V.

Copyright © 2012, Texas Instruments Incorporated

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