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SLVAFG6B December 2022 – November 2024 TPS25762-Q1 , TPS25763-Q1 , TPS25772-Q1

5.2 Fair Share Power Policy Example

This section provides examples of power sharing between two ports configured with Fair Share Power Policy and when connected to Port Partners that are Good Sinks. When Port Partners are Good Sinks, the power distribution is the same whether Blind Sink Support is enabled or disabled. Table 5-10 shows the SPM Engine parameters used in this section's example. The FSP Parameters shown in Table 5-4 are used in the power distribution method and to achieve FSP between two Sinks.

Table 5-3 SPM Engine Parameters - FSP Example With Good Sinks

SPM Engine Parameters	Configuration	Description
System Max Power	75W	Total system power capacity allocated for Port A and B
Port A Max Power	60W	Maximum Port A Power
Port B Max Power	60W	Maximum Port B Power
Port A Min Power	15W	Minimum Port A power
Port B Min Power	15W	Minimum Port B power
Shared Mode	Fair Share Power Policy without Blind Sink Support	Port Min Power is guaranteed for each port and remaining power is intelligently distributed

Table 5-4 Fair Share Power Policy Parameters

Fair Share Power Policy Parameters	Value	Description
Equally Divided Shared Power	(75-(15+15))/2=22.5W	Equally shared power for each port that can be distributed: (Total VBUS power – Sum of Port A and B's Min Power)/Total number of ports
Per Port Guaranteed FSP	15+22.5W=37.5W	Guaranteed Shared Power for each port: Equally Divided Shared Power + Port Min Power

Four example scenarios of Fair Share Power Policy power distribution are concisely summarized in Table 5-5.

Table 5-5 FSP Example with Good Sinks

	Port A	Port B
Initially Allocated	15W	15W
Scenario 1: Port A connects to a Sink that requires 60W. Port B is unconnected.
Power Required by Sink	60W
Power Distributed to Sink	60W
Scenario 2: Port B connects to a Sink that also requires 60W Sink Cap.
Power Required by Sink	60W	60W
Power Distributed to Sinks⁽¹⁾	37.5W	37.5W
Scenario 3: Port B changes the requirement to 15W.
Power Required by Sink	60W	15W
Power Distributed to Sinks⁽²⁾	60W	15W
Scenario 4: Port B changes the requirement to 25W.
Power Required by Sink	60W	25W
Power Distributed to Sinks⁽³⁾	50W	25W

(1) Per Port Guaranteed FSP of 37.5W are distributed. See second example scenario in Table 3-3.

(2) Distribute 15W to Port B and reallocate surplus power 22.5W from Port B to Power Reserve (Per Guaranteed FSP of 37.5W - Power Distributed to Port B 15W = 22.5W). Port A is now granted with 22.5W power from Power Reserve and therefore able to fulfill 60W power request.

(3) 10W from Port A is yielded and redistributed to Port B. See the third example scenario in Table 3-3.

Figure 5-3 and Figure 5-4 show the PD negotiation flow following the FSP examples from Scenario 1 and Scenario 2 of Table 5-5, respectively.

Figure 5-3 FSP Negotiation Flow - Scenario 1

Figure 5-4 FSP Negotiation Flow - Scenario 2