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TPS65987D: Behavior when the VBUS1 pin is OPEN

user1866475
Intellectual 350 points
Part Number: TPS65987D
Other Parts Discussed in Thread: TPS65987,

Hi all,

What is the behavior when the VBUS1 pin is OPEN?

The datasheet says to connect VBUS1 and VBUS2. Why?

I considered PP_HV1-VBUS1 and PP_HV2-VBUS2 as just load switches. However, when configured as a power source device and using only the PP_HV2-VBUS2 path, with PP_HV1 connected to GND and VBUS1 OPEN, and PP1 configuration is set to Disabled.  The TPS65987 did not work correctly. It became to work like a non-Power Delivery device, simply supplying VBUS. Why?

From there connect VBUS1 and VBUS2 and it will work properly Power Delivery.

Can you outline to me how the potential given to VBUS1 is used inside the device? The pin description in table 5-1 in the datasheet is too much of a black box, just stating "Connect VBUS1 and VBUS2".

If I design it based on your datasheet it will work correctly. However, if I have more information about the behavior, it will help me in my analysis when I face various failures..

Best Regards,

Yukio Oyama

  • 0
    TI__Mastermind 37855 points

    Hi Yukio-san,

    user1866475 said:
    The datasheet says to connect VBUS1 and VBUS2. Why?

    VBUS1 contains the sense circuitry, so must be connected for proper operation.

    Thanks and Regards,

    Chris

  • 0 in reply to Christopher Lim1
    Intellectual 350 points

    Hello Chris-san,

    Your answer does not satisfy me because it only states the result of the operation in reverse.

    The fact that the presence or absence of voltage affects the device operation shows that I have some sense of what it is. And since the power path detects current I can imagine there is some kind of sense circuitry. 


    What does the power path detect and why does it interfere with the operation even if it is set to disable?
    What is the purpose of the sense and how does the operation behave depending on the detected value?

    Can you explain its behavior (mechanism) to me, just at the block diagram level?

    Best Regards,

    Yukio Oyama

  • 0 in reply to user1866475
    TI__Mastermind 37855 points

    Hi Yukio-san,

    Let me reach out to the device expert to get more information.

    Thanks and Regards,

    Chris

  • 0 in reply to Christopher Lim1
    TI__Mastermind 37855 points

    Hi Yukio,

    Internal to the device, the voltage sense, OVP, and Undervoltage sense circuitry is only enabled on VBUS1. The 987 does not have sense circuitry enabled on VBUS2. For the PD to operate properly, the sense circuitry needs to be connected, which is why we require VBUS1 and VBUS2 to be connected. When negotiating contracts, we first monitor the voltage to make sure we are providing the nominal value, and after negotiated, we monitor to prevent ovp or undervoltage events.

    Thanks and Regards,

    Chris

  • 0 in reply to Christopher Lim1
    Intellectual 350 points

    Hello Chris-san,

    Is the voltage sensing on the VBUS1 pin always monitored regardless of source, sink or disable settings?
    Also, when I set the VBUS1 pin to OPEN, the TPS65987D simply supplied VBUS without any Power Delivery negotiation action (I have VBUS connected to the VBUS2 pin).
    Is the behavior of supplying VBUS when the VBUS1 pin is OPEN, without the Power Delivery negotiation operation, correct IC behavior?

    Please point out if you need additional information to help you determine that.

    Best Regards,

    Yukio Oyama

  • +1 in reply to user1866475
    TI__Mastermind 37855 points

    Hi Yukio,

    user1866475 said:
    Is the voltage sensing on the VBUS1 pin always monitored regardless of source, sink or disable settings?

    The sensing will be on during PD operation and when the switch is closed (including non-PD). It could potentially be on when PD is disabled if you are still using type-C.

    user1866475 said:
    Is the behavior of supplying VBUS when the VBUS1 pin is OPEN, without the Power Delivery negotiation operation, correct IC behavior?

    Having VBUS1 OPEN is not within the expected behavior. After speaking with Systems, we do not have a "correct IC behavior" when VBUS1 is diconnected like this due to it being outside of expected operating conditions.

    Thanks and Regards,

    Chris

  • 0 in reply to Christopher Lim1
    Intellectual 350 points

    Hi Chris-san,

    I understood that when VBUS1 is OPEN, the device behavior is unpredictable.

    Thanks for your persistent support, it is much appreciated.

    If you can, please add to the datasheet why the VBUS1 pin should always be connected to VBUS (e.g. VBUS voltage is monitored by the VBUS1 pin)

    Best Regards,

    Yukio Oyama