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

5.2.2 FSP Policy Example – Blind Sink Support With Max Power

This section provides three additional examples of Fair Share Power Policy's power distribution, but with Blind Sink Support and Max Power enabled for both ports, and are shown in Table 5-9. With these two FSP settings enabled, Port Max Power is always advertised after the initial Source Capabilities message regardless of the Sink's behavior. The SPM Engine Parameters for these examples are the same as shown in Table 5-6

Table 5-9 FSP Example With Blind Sink Support and Max Power

	Port A	Port B	SPM Operation Description
Initially Allocated	15W	15W	Min Power is initially allocated for Port A and Port B.
Scenario 1: Port A connects to Good Sink 1. Port B is unconnected.
Source Cap 1	15W		The first Source Cap is sent to Port A's Sink with Port Min Power.
Sink Request	15W		Grant 15W to Port A.
Sink Cap	45W		Source sends Get Sink Cap message to Port A and max 45W Sink Cap is returned.
Source Cap 2	60W		Source Cap is sent again with Port Max Power since Max Power is enabled.
Sink Request	60W		Port A Sink requests 60W.
Power Distributed to Sink	60W		60W delivered to Port A Sink.
Scenario 2: Port A is replaced with a Blind Sink. Port B is still unconnected.
Source Cap 1	15W		The first Source Cap is sent to Port A's Sink with Port Min Power.
Sink Request	15W		Grant 15W to Port A.
Sink Cap	15W		Source sends Get Sink Cap message to Port A. Source Cap = Sink Cap is returned, but is a don't care with Max Power enabled.
Source Cap 2	60W		A Source Cap is sent again with Port Max Power.
Sink Request	60W		Port A Sink requests 60W.
Power Distributed to Sink	60W		60W is distributed to Port A Sink.
Scenario 3: Port B connects to Good Sink 2. Port A continues to deliver 60W to Blind Sink.
Source Cap 1		15W	The first Source Cap is sent to Port B's Sink with Port Min Power.
Sink Request		15W	Grant 15W to Port B.
Sink Cap		20W	Source sends Get Sink Cap message to Port B and max 20W Sink Cap is returned.
Source Cap 2	37.5W	37.5W	Max Power is enabled, so Per Port Guaranteed FSP is advertised to both Sinks regardless of Sink Capabilities.
Sink Request	37.5W	37.5W	Port A and B's Sinks request 37.5W.
Power Distributed to Sinks	37.5W	37.5W⁽¹⁾	Each Sink gets Per Port Guaranteed FSP of 37.5W.

(1) Some Sink devices return a Sink Capabilities message that is lower than what they are actually able to consume. The Max Power option can be adopted to support higher power charging for Sink devices such as these.

Figure 5-8, Figure 5-9, and Figure 5-10 show the PD negotiation flow of the FSP examples from Scenario 1, Scenario 2, and Scenario 3 of Table 5-9, respectively.

Figure 5-8 FSP Negotiation With Blind Sink Support and Max Power - Scenario 1

Figure 5-9 FSP Negotiation With Blind Sink Support and Max Power - Scenario 2

Figure 5-10 FSP Negotiation With Blind Sink Support and Max Power - Scenario 3