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TPS65986: How to set "Higher Capability" bit on PDO

Eric S
Expert 5640 points
Part Number: TPS65986


Our device has up to 18W operating power (periodically). Although we still want to advertise a 5V@3A sink PDO since that's better than nothing, it should be considered a "capability mismatch" because we can't fully operate off 15W alone.

 

We think the correct way to encode this is to set bit 28 (Higher Capability) in the 5V@3A sink PDO.

 

However, this isn't exposed in the GUI tool. The most promising setting is ANSinkMinRequiredPower (bits 9:0 in 0x37 Auto Negotiate Sink) which is documented as "Minimum operating power required by the Sink in 250mW per LSB. Typically, this field is set to the maximum power across the PDOs defined in the TX Sink Capabilities Register (0x33)."

 

The 1st sentence of this documentation ("minimum operating power" which is what we want) seems to contradict the second sentence ("maximum power across the PDOs"). Also, this is not exposed in the GUI tool either.

 

Do you think we could get some clarity on how to configure the minimum operating power?

  • 0
    TI__Expert 5640 points
    Some update to this question.....
    • We discovered that ANSinkMinRequiredPower does appear to be exposed in GUI: if we uncheck "Automatically Calculate Min Power Required" in the Autonegotiate Sink pane, a new setting named "Minimum Power Required" appears.
    • We have gotten TPS65986 to set the 'Higher' bit with "Automatically Calculate Min Power Required" checked, one (5V/3A operating/3A min/3A max) fixed PDO, and one (9-20V/3A operating/3A min/3A max) variable PDO. Presumably the recommendation in the documentation is applied when this box is checked, and "Automatically Calculate Min Power Required" causes the minimum power to be set to 60W?
  • 0 in reply to Eric S
    TI__Expert 4415 points

    Hi Eric,

    From my understanding, you want to set the sink more than 15W power when the voltage stays on 5V, is it right? If so, it doesn't meet the PD specs shown as below. When the power exceeds 15W but within 27W, the voltage has to be 9V. We do not recommend any settings that cannot pass PD compliant test.

    Best Regards,

    Hao

  • 0 in reply to Hao Wang14
    TI__Expert 5640 points
    Clarification, they can supplement with an on-board battery, so even though they may consume say 18W, if there is ONLY a 5V/3A PDO available, they want to accept that PDO, and supplement the system with additional 3W from their battery.

    In order to do this, as I understand, if the Source Queries for Sink Capabilities, they would want to advertise the 5V/3A PDO with the "Higher Capability" bit set. That way, if there is a higher power PDO available, the Source should offer it. But, if the Source is only capable of 5V/3A, then it will offer that, and the Sink can accept it. If they ONLY advertise 9V-20V PDO for >15W requirement, then a Source with only 5V/3A available would not successfully negotiate a contract with this Sink, right?

    Similarly, it seems if the Source advertises it's capabilities (in this example, 5V/3A only), instead of querying for Sink Capabilities, they would respond with an RDO of 5V/3A, but with the "Capability Mismatch" bit set, is this correct? Higher Capability and Capability Mismatch seem to provide the same utility, but one is within the Sink PDO, and the other is within the Sink RDO structure. Am I understanding things correctly?

    If my understanding is correct, then are they following the correct process to set that "Higher Capabliity" bit in the tool, per my 2nd post, but it doesn't seem right that "Auto calculate min power" is now setting the power to 60W. Please advise.
  • 0 in reply to Eric S
    TI__Expert 4415 points
    Hi Eric,

    It's really a creative way to do it, I agree with your analysis and your settings. It might work this way, but we do not recommend setting “higher capability”.

    Best Regards,
    Hao