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TPS66020, TPS66021

SLVSEW8 – AUGUST 2019

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9.2.3 Dead Battery Support

The TPS6602x integrates a high-voltage VBUS LDO that can be used to supply power to a PD Controller and

other supporting circuitry when only VBUS power is available, such as in a dead battery condition. As shown in

Figure 20, the TPS66020 VLDO output supplies power to the PD Controller's 3V_IN supply. Similarly, Figure 19

shows the TPS66021 VLDO output supplies power to the PD Controller's 5V_IN supply. During a dead battery

condition, the PD Controller presents its Type-C RPD pull-downs on the CC1 and CC2 lines. Upon connection to

a Type-C/PD Source, 5 V is provided to VBUS from the Source partner which powers the TPS6602x. The VBUS

LDO is enabled and provides power to the PD Controller. Once powered, the PD Controller can decide to enable

the TPS6602x PPHV Sink path by asserting EN0 high and use the 5-V VBUS to charge the battery or it may

choose to negotiate a higher voltage contract first. Either way, once the contract is negotiated, the PD Controller

will enable the PPHV Sink path and charge the system. Once the system is sufficiently charged, the VIN terminal

VLDO will be supplied from VIN and the VBUS LDO will be disabled.

9.2.4 Fast Role Swap (FRS) (Optional)

The TPS6602x supports Fast Role Swap operation as in the new Source, old Sink scenario shown in Figure 15.

The PPHV power path represents the old Sink and the PP5V power path represents the new Source. During

FRS, the PP5V power path of the TPS6602x has a much faster turn-on compared to normal operation, for

example entering SRC 1P5A or SRC 3P0A states from the DISABLED state. This faster turn-on is required in

order to meet the USB PD fast role swap timing requirements (tSrcFRSwap) for the new Source.

To enable FRS, the TPS6602x must first be operating as a Sink (SNK state). The TPS6602x must then transition

to the FRS state by asserting EN1 high. EN1 is asserted high by the PD Controller as soon as possible once it

has properly detected FRS signaling from its port partner on its CC line. The FRS signaling from the port partner

to the PD Controller indicates that the port partner has lost its power and requires a fast role swap sequence to

be performed.

It should be noted that the timing of when EN1 is asserted high relative to the port partner losing power is highly

application, and implementation dependent. Some of these dependencies include:

•

Loss of power detection accuracy, margin and propagation delay of the port partner.

•

Timing from loss of power detection to FRS signaling transmitted on the CC line.

•

Detection by the PD Controller of the FRS signaling received on its CC line.

•

Assertion of a GPIO from the PD Controller after detection of the FRS signaling.

In systems that require good FRS performance, these should be optimized to minimize unnecessary delays from

significantly impacting the turn-on of the new Source. Once the FRS state is entered, the TPS6602x will

automatically handle the power role swap from Sink to Source as shown in Figure 16. In most applications, there

is significant charge being stored in reserve while power is being provided. Upon loss of power, this charge is

then used to supply power to the application until the FRS completes. As this charge depletes, the voltage on

VBUS will decay at some rate based on the current load and the amount of charge that has been stored. USB

PD requires that the new Source only be enabled once VBUS is detected below vSafe5V (maximum). Therefore,

the amount of voltage that VBUS drops below vSafe5V will depend heavily on the amount of remaining charge

and what current load is on VBUS, along with how fast the PP5V power path can enable. It should be noted that

the PD Specification allows VBUS to be discharged completely to ground and is shown in typical response curve.