Disabled

Enabled

Disabled

EN1_EN0

PP5V to VBUS (SRC)

VBUS to PPHV (SNK)

Disabled

00b

01b

00b

t

OFF_PPHV

t

ON_PPHV

t

DG_EN

t

DG_EN

Enabled

3 A ILIMIT

Disabled

Enabled

Disabled

EN1_EN0

PP5V to VBUS (SRC)

VBUS to PPHV (SNK)

Disabled

00b

01b

00b

11b

10b

Disabled

00b

t

OFF_PPHV

t

ON_PP5V

t

ON_PPHV

t

OFF_PP5V

Enabled

1.5 A ILIMIT

t

DG_EN

t

DG_EN

t

DG_EN

t

DG_EN

24

TPS66020, TPS66021

SLVSEW8 – AUGUST 2019

www.ti.com

Product Folder Links: TPS66020 TPS66021

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Copyright © 2019, Texas Instruments Incorporated

Figure 13. Changing the PP5V Source Path from 3-A to 1.5-A Current Limit

8.7.6 Enabling the PPHV Sink Path

The timing diagram of enabling the PPHV Sink path is shown in Figure 14. As stated earlier, transitions from the

either the Source path to the Sink path or vice-versa always requires a transition first to the DISABLED state,

EN1_EN0 = 00b.

Figure 14. Enabling the PPHV Sink Path

8.7.7 Fast Role Swap (FRS)

8.7.7.1 Overview

For a hub application, the hub may be supplied by an external power source that is supplying power to a Host

(via the Source path of the dual-role power (DRP) of the hub), as well as, a downstream Bus Powered Device

(BPD) (DFP Source to the BPD). A communication path is formed from Host to the Bus Powered Device. Prior to

FRS, power flows from the external power source to the Host and the Bus Powered Device. If the external power

is removed, FRS operation will attempt to change the power role of the Host to a Source and the hub DRP port

to a Sink allowing power to change direction from the Host to the BPD in an attempt to maintain the connection.

It should be noted that after FRS, the contract is 5 V. Refer to the PD3.0 specification for further details on the

Fast Role Swap function.

Two PD controllers are used in the FRS process. One PD controller resides on the Host side (USB PD Capable

Host); the other resides on the hub side (USB PD Capable Hub). Both PD controllers are DRP since they must

support power role swapping. Prior to FRS, the Hub DRP is a Source (known as the old Source) and may be

supplying power to the DRP Host, which is acting as a Sink (known as the old Sink). After FRS, the Host DRP is

a 5-V Source (known as the new Source, old Sink), and is supplying power to the Hub DRP configured as a Sink

(known as the new Sink, old Source).