TPS2540, TPS2540A

TPS2541, TPS2541A

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SLVSAG2C

– OCTOBER 2010 – REVISED OCTOBER 2011

Standard Downstream Port (SDP) USB 2.0

An SDP is a traditional USB port that follows USB 2.0 and supplies a minimum of 500 mA per port. USB 2.0

communications is supported, and the host controller must be active to allow charging.

Charging Downstream Port (CDP)

A CDP is a USB port that follows USB 2.0 BC1.2 and supplies a minimum of 1.5 A per port. It provides power

and meets USB 2.0 requirements for device enumeration. USB 2.0 communications is supported, and the host

controller must be active to allow charging. What separates a CDP from an SDP is the host-charge handshaking

logic that identifies this port as a CDP. A CDP is identifiable by a compliant BC1.2 client device and allows for

additional current draw by the client device.

The CDP hand-shaking process is two steps. During step one 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

an 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.

The second step is necessary for portable equipment to determine between a CDP and a DCP. The portable

device 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 CDP if the data line being read remains less than the nominal data detect

voltage of 0.3 V. The portable device concludes it is connected to a DCP if the data line being read is greater

than the nominal data detect voltage of 0.3V and less than 0.8 V.

Dedicated Charging Port (DCP)

A DCP is a special type of wall-adapter used in charging applications that uses a micro-B connector to connect

to portable devices. A DCP only provides power and cannot enumerate upstream facing portable equipment. It

does not support USB 2.0 communications, but it does provide specific impedances on the data lines reserved

for USB 2.0 so that it is identifiable as a dedicated charger.

The impedances presented on D+ and D- are different depending on the specific standard the dedicated charger

is designed to. BC1.2 and the Chinese Telecommunications Industry Standard YD/T 1591-2009 define that the

D+ and D- data lines should be shorted together with a maximum series impedance of 200

Ω.

On the other hand, with the divider mode, 2 V and 2.7 V are presented on D+ and on D-.

The TPS2540/40A/41/41A integrates an auto-detect feature that supports both DCP schemes. It starts in Divider

Mode. If a BC1.2 -compliant device is attached, the TPS2540/40A/41/41A responds by discharging OUT, turning

back ON the power switch and operating in BC1.2 DCP mode. It then stays in that mode until the device is

unattached, in which case it goes back to Divider Mode.

High-Bandwidth Data Line Switch

The TPS2540/40A/41/41A passes the D+ and D- data lines through the device to enable monitoring and

handshaking while supporting charging operation. A wide bandwidth signal switch is used, allowing data to pass

through the device without corrupting signal integrity. The data line switches are turned on in any of CDP or SDP

operating modes. The EN (or DSC if TPS2541/41A) input also needs to be at logic High for the data line

switches to be enabled.

NOTE

1. While in CDP mode, the data switches are ON even while CDP handshaking is occurring.

2. The data line switches are OFF if EN (or DSC) is low, or if in DCP mode (BC1.2, Divider mode

or Auto-detect). They are not automatically turned off if the power switch (IN to OUT) is doing

current limiting. With TPS2540/40A, the data line switches are also off when in

“000” mode.

3. The data switches are for USB 2.0 differential pair only. In the case of a USB 3.0 host, the

super speed differential pairs must be routed directly to the USB connector without passing

through the TPS2540/40A/41/41A.

Copyright

© 2010–2011, Texas Instruments Incorporated

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