Power Source Performance if EMCA has Source Incompatibility - KBA218956

Version: **

 

Question:

What is the power source performance if the attached EMCA cable has incompatible source capabilities?

 

Answer:

First, the source changes the current of source Power Date Objects (PDOs) to follow the EMCA’s capabilities. If the PDOs’s current is higher than the VBUS Current Handling Capability of the attached EMCA cable, then the power source will disable the source PDOs. If the voltage capability of thePDOs is higher than the maximum VBUS voltage of the attached EMCA cable, then the power source checks if the Modal Operation is supported to confirm whether the attached cable can support the Alternate Mode. After that, the power source starts advertizing about its capabilities by sending Source_Capabilities Messages at regular intervals.

 

Detailed Explanation:

 

  1. When the cable is attached (no PD Connection or Contract yet):

     

    The power source typically sets VBUS to ‘vSafe5V’ after it detects Rd on the CC line.

  2. Prior to PD connection (no PD Connection or PD Contract yet):   
    1. The power source sets VCONN to 5 V after it detects Ra on CC line.
    2. It then attempts to communicate with one of the cable plugs using SOP’ Packets with Discover Identity Command.
    3. The EMCA cable sends back the ACKs using SOP’ Packets with an ID Header VDO, a Cert Stat VDO, a Product VDO, and the Product Type VDOs defined by the Product Type as shown in the following table.
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    4. The source then checks for Modal Operation support (B26 of ID Header VDO), maximum current (B6 and B5 of Cable VDO), and maximum voltage (B10 and B9 of Cable VDO, PD3.0 only) to confirm whether the attached EMCA can support Alternate Mode along with maximum current and voltage values.
    5. The power source will then change the current of active PDOs and disable the PDOs whose voltages cannot be supported by EMCA.
  3. The power source begins to periodically advertise its capabilities (the capabilities comes from step ‘e’) by sending Source_Capabilities messages every at regular intervals defined by the variable: tTypeCSendSourceCap (min: 100 ms, max: 200 ms).