UCS3205 datasheet(17/30 Pages) MICROCHIP

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DS20006433A-page 17

UCS3205

4.9

Fast Role Swap (FRS)

The Fast Role Swap circuit enables the application to

change the role of sinking current to sourcing current

within the allowed time defined by the USB Power

Delivery Specification. The FRS circuit is pre-enabled

when the FRS pin is pulled high for the duration of

tFRS_PREARM and remains in this Ready state as long

as the FRS pin remains high. All Fault protections

remain active, but the FAULT# pin and associated Fault

Handling states are not asserted unless EN = 1.

Pre-enabling the FRS is valid only in a Reset state

(EN = 0). A low-to-high FRS transition received while

EN = 1 will not affect operation. If FRS = 1 and in a

Reset state (EN = 0), the UCS3205 will then monitor

the EN pin for a low-to-high transition. A low-to-high

transition on EN will fully enable the FRS circuit and the

switch will be turned on in tFRS_SWAP after VOUT drops

below VIN. When tFRS_SWAP elapses, the application’s

VOUT voltage will be above 90% of the VIN voltage. Any

high-to-low transitions on the FRS pin are ignored

during FRS conditions. A high-to-low transition on EN

will turn off the switch and exit FRS. See Figure 4-2,

Figure 4-3, and Figure 4-4.

FIGURE 4-2:

Fast Role Swap – Nominal Operation.

FIGURE 4-3:

Fast Role Swap – FRS Circuitry Remains Awake.

T = 200 μs

FRS

FRS pulled high to

wake up UCS3205

Milliseconds,

hours or days

elapsed

FRS transi on

Controller pulls FRS low with

EN to get low-IQ or to allow

next start-up to be normal (non-

FRS)

PD controller detects FRS

request and arms UCS3205

T < 150 μs is possible for

fast falling VOUT

FRS =

0 has no

once the

switch is on

T = 200 μs

FRS

FRS pulled high to

wake up UCS3205

Milliseconds,

hours or days

elapsed

FRS transi on

PD controller detects FRS

request and arms UCS3205

T << 150 μs total

UCS3205 will enter Reset state but

internal analog circuitry will stay

(woken up) and ready for next FRS

request. No BVD Fault response

(anyway, switch is

)

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