SLVAFG6A December   2022  – November 2023 TPS25762-Q1 , TPS25772-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
    1. 1.1 Terms and Abbreviations
  5. 2 SPM Engine Overview
  6. 3Multi-Port Power Allocation Policy
    1. 3.1 Assured Capacity Policy
    2. 3.2 Shared Capacity Policy
      1. 3.2.1 Fair Share Power Policy
        1. 3.2.1.1 Blind Sink Support
    3. 3.3 Hybrid Mode
  7. 4Power Foldback Policy
    1. 4.1 Thermal Foldback Operation
    2. 4.2 Engine Start or Stop Transition Management
      1. 4.2.1 Engine Start or Stop Power Foldback Operation Example
  8. 5Multi-Port Power Allocation Policy Examples
    1. 5.1 Assured Capacity Policy Example
    2. 5.2 Fair Share Power Policy Example
      1. 5.2.1 FSP Policy Example – Blind Sink Support
      2. 5.2.2 FSP Policy Example – Blind Sink Support with Max Power
    3. 5.3 Hybrid Mode Example
  9. 6References
  10. 7Revision History

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
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 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=22.5 W 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+22.5 W=37.5 W 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 15 W 15 W
Scenario 1: Port A connects to a Sink that requires 60 W. Port B is unconnected.
Power Required by Sink 60 W
Power Distributed to Sink 60 W
Scenario 2: Port B connects to a Sink that also requires 60 W Sink Cap.
Power Required by Sink 60 W 60 W
Power Distributed to Sinks(1) 37.5 W 37.5 W
Scenario 3: Port B changes the requirement to 15 W.
Power Required by Sink 60 W 15 W
Power Distributed to Sinks(2) 60 W 15 W
Scenario 4: Port B changes the requirement to 25 W.
Power Required by Sink 60 W 25 W
Power Distributed to Sinks(3) 50 W 25 W
(1) Per Port Guaranteed FSP of 37.5 W are distributed. See second example scenario in Table 3-3.
(2) Distribute 15 W to Port B and reallocate surplus power 22.5 W from Port B to Power Reserve (Per Per Guaranteed FSP of 37.5 W - Power Distributed to Port B 15 W = 22.5 W). Port A is now granted with 22.5 W power from Power Reserve and therefore able to fulfill 60 W power request.
(3) 10 W 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.

GUID-20221004-SS0I-75CW-B1XC-RQP6W1MQGMWQ-low.png Figure 5-3 FSP Negotiation Flow - Scenario 1
GUID-20221004-SS0I-C3D4-0RLQ-3FCJL7RHWVFB-low.png Figure 5-4 FSP Negotiation Flow - Scenario 2