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DS00002838B-page 19

UPD301A

4.3.2

DFP OPERATION

The device implements current sources to advertise current charging capabilities on both CC pins when operating as a

DFP.

When a UFP connection is established, the current driven across the CC pins creates a voltage across the UFP’s Rd

pull-down that can be detected by the integrated CC comparator. The voltages monitored are summarized in Table 4-

3. When connected to an active cable, an alternative pull-down (Ra) appears on the CC pin.

The DFP also integrates two 5V FETs for implementing the VCONN function. This is further discussed in Section 4.3.5,

"VCONN Operation".

4.3.3

RP CURRENT SOURCES

In order to advertise the current charging capabilities of the device via the integrated port power controller or external

power circuit, Rp current sources are used. The current source can be selected by software. Table 4-4 summarizes the

values supported by the current sources in regards to the programmed value.

4.3.4

COLLISION AVOIDANCE

An alternative mode of operation is required to enable the CC detection circuit to facilitate software implementation of

collision detection which was incorporated into version 3.0 of the USB PD Specification.

In order to avoid message collisions due to asynchronous Messaging (AMS) sent from the Sink, the Source sets Rp to

SinkTxOk (3A@5V) to indicate to the Sink that it is OK to initiate an AMS. When the Source wishes to initiate an AMS

it sets Rp to SinkTxNG (1.5A@5V). When the Sink detects that Rp is set to SinkTxOk it may initiate an AMS. When the

Sink detects that Rp is set to SinkTxNG it shall not initiate an AMS and shall only send Messages that are part of an

AMS the Source has initiated.

TABLE 4-3:

SOURCE DETECTION

CC1

CC2

Connection State

CC Comparator State

VBUS

VCONN

Open

Open

Nothing Attached

Monitor both CC pins for attach

Off

Off

Rd

Open

UFP Attached

Monitor CC1 for detach

On

Off

Open

Rd

UFP Attached

Monitor CC2 for detach

On

Off

Ra

Open

Powered Cable, No UFP attached

Monitor CC2 for UFP attach.

Monitor CC1 for cable detach.

Off

Off

Open

Ra

Powered Cable, No UFP attached

Monitor CC1 for UFP attach.

Monitor CC2 for cable detach.

Off

Off

Ra

Rd

Powered Cable, UFP attached

Monitor CC2 for UFP detach.

CC1 is not monitored for detach.

On

On

Rd

Ra

Powered Cable, UFP attached

Monitor CC1 for UFP detach.

CC2 is not monitored for detach.

On

On

Rd

Rd

Debug accessory mode attached

Monitor both CC pins for detach

Off

Off

Ra

Ra

Audio accessory mode attached.

Monitor both CC pins for detach

Off

Off

TABLE 4-4:

RP CURRENT SOURCES

DFP Advertisement

Current source

(1.7V to 5.5V)

RPx Value

Disabled

00b

Default USB Power

80 uA +/-20%

01b

1.5A @ 5V

180 uA +/-8%

10b

3.0A @ 5V

330 uA +/-8%

11b