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

3.2 Shared Capacity Policy

The Shared Capacity Policy is where the sum of the Port Max Power, as designed, is less than the Total USB VBUS Power. When the Source ports are configured in Shared Capacity, Port Min Power is guaranteed for each port while the remaining power stored in Power Reserve is shared between Port A and Port B.

Equation 2. Total USB VBUS Power = Port A Min power + Port B Min power + Power Reserve

An example of the Shared Capacity Policy is shown in Figure 3-6 where the Total USB VBUS Power is 75 W, Port A and B's Min Power are both 15 W, and there is 45 W in Power Reserve. Port A connects to a Sink that requests 45 W. Port A's Min Power of 15 W is guaranteed, so 30 W is distributed from Power Reserve to deliver a total of 45 W, the Sink's requested power. The remaining power in Power Reserve is now 15 W, so with Port B's Min Power of 15 W, a total of 30 W is available for Port B. From this point, what occurs when a second Sink connects to Port B is dependent on the Port Partner's Sink Capabilities and is discussed in the following subsections.

GUID-20230829-SS0I-6SVQ-X57M-TZ0VQJN1LFGC-low.png Figure 3-6 Shared Capacity Policy

Figure 3-7 and Figure 3-8 show the Shared Capacity Policy selection in the GUI's Simple Configuration view and Advanced Configuration view.

GUID-20230828-SS0I-P9KK-NV4S-RZPQ04FNMBVQ-low.png Figure 3-7 Shared Capacity GUI Selection – Simple Configuration
GUID-20230828-SS0I-X5CL-FLN4-PJHGZQKHS83N-low.png Figure 3-8 Shared Capacity GUI Selection – Advanced Configuration

Note that although freely configurable in the GUI, according to the USB Type-C Cable and Connector Specification Release 2.2, the following behavioral rules must apply for Source ports configured with Shared Capacity Policy:

  • Both Source ports must have the same power capabilities; each port must be capable of the same Port Max Power, Port Min Power, and able to harvest power from Power Reserve equally.
  • Port Min Power must be at least 7.5 W.
  • Ports that initially offer 1.5 A must increase to 3 A after a connection with a Sink if there is sufficient power remaining in Power Reserve within one second.