SLVAFG6A December 2022 – November 2023 TPS25762-Q1 , TPS25772-Q1
This section provides examples of Fair Share Power Policy's power distribution with Blind Sink Support enabled for both ports and in the event of a port connecting to a Sink that fails to return Sink Capabilities correctly. Note that the Max Power option is not enabled in these examples. Table 5-6 shows the SPM Engine parameters used in this section's example. The FSP Parameters shown in Table 5-7 are used in the Fair Share Power Policy's power distribution to achieve FSP between two Sinks.
SPM Engine Parameters | Configuration | Description |
---|---|---|
Total USB VBUS Power (System Max Power) | 75 W | Total system power capacity allocated for Port A and B |
Port A Max Power | 60 W | Maximum Port A Power |
Port B Max Power | 60 W | Maximum Port B Power |
Port A Min Power | 15 W | Minimum Port A power |
Port B Min Power | 15 W | Minimum Port B power |
Shared Mode | FSP with Blind Sink Support | Port Max Power is offered to Blind Sinks |
Fair Share Power Policy Parameter | Value | Description |
---|---|---|
Equally Divided Shared Power | (75-(15+15))/2=22.5 W | Shared power for each port that can be distributed if available: (Total VBUS power – Sum of Port A and B's Min Power)/Total number of ports |
Per Port Guaranteed FSP | 15+22.5 W=37.5 W | Port Min Power + Per Port Equally Divided Shared Power = Per Port Guaranteed FSP |
Three example scenarios of Fair Share Power Policy operation (when Blind Sink Support is enabled) are shown in Table 5-8. The table format in this section is structured differently to show how Blind Sinks are handled and supported by the SPM.
Port A | Port B | SPM Operation Description | |
---|---|---|---|
Initially Allocated | 15 W | 15 W | 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 | 15 W | The first Source Cap is sent to Port A's Sink with Port Min Power. | |
Sink Request | 15 W | Grant 15 W to Port A. | |
Sink Cap | 45 W | Source sends Get Sink Cap message to Port A and max 45 W Sink Cap is returned. | |
Source Cap 2 | 45 W | A 45 W Source Cap is sent again based on Sink Cap. | |
Sink Request | 45 W | Port A Sink requests 45 W. | |
Power Distributed to Sink | 45 W | 45 W distributed to Port A Sink. | |
Scenario 2: Port A is replaced with a Blind Sink. Port B is still unconnected. | |||
Source Cap 1 | 15 W | The first Source Cap is sent to Port A's Sink with Port Min Power. | |
Sink Request | 15 W | Grant 15 W to Port A. | |
Sink Cap | 15 W | Source sends Get Sink Cap message to Port A. Source Cap = Sink Cap is returned. Port A Sink is identified as a Blind Sink. | |
Source Cap 2 | 60 W | A Source Cap is sent again with Port Max Power. | |
Sink Request | 60 W | Port A Sink requests 60 W. | |
Power Distributed to Sink | 60 W | 60 W is distributed to Port A Sink. | |
Scenario 3: Port B connects to Good Sink #2. Port A continues to deliver 60 W to Blind Sink. | |||
Source Cap 1 | 15 W | The first Source Cap is sent to Port B's Sink with Port Min Power. | |
Sink Request | 15 W | Grant 15 W to Port B. | |
Sink Cap | 20 W | Source sends Get Sink Cap message to Port B and max 20 W Sink Cap is returned. | |
Source Cap 2 | 55 W | 20 W | Port A Sink's required power is less than the Per Port Guaranteed FSP. Port B's required power is higher. The SPM distributes power to the Port A's Sink requesting lower power and the remaining power to Port B's Sink. |
Sink Request | 55 W | 20 W | Port A Sink requests 55 W and Port B Sink requests 20 W. |
Power Distributed to Sinks | 55 W | 20 W | 55 W distributed to Port A Sink. 20 W distributed to Port B Sink. |
Figure 5-5, Figure 5-6, and Figure 5-7 show the PD negotiation flow of the FSP examples from Scenario 1, Scenario 2, and Scenario 3 of Table 5-8, respectively.