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TPS65987D: Power and Current Limiting questions

Brian Angiel
Expert 4060 points
Part Number: TPS65987D
Other Parts Discussed in Thread: TIDA-050014

I would like to power TPS65987D from VBUS1, since there is no system 3.3V available in my design. Should VIN_3V3 be left as no connect in that case, or is a decoupling cap needed on that input? 

I also wanted to clarify the current limiting capability of TPS65987D. According to the datasheet, the power switch has overcurrent protection at Iocp, which is 10A, but I did not see a configurable overcurrent limit lower than that when operating as a sink. There is a firmware configurable overcurrent clamp, Iocc,  but only when operating as a source (see Section 8.3.3.1.1). Do I need an external fuse, then, if I want to implement a lower OCP limit (e.g., 1A or 1.5A) for PD sink?

Thanks,

Brian Angiel

  • 0
    TI__Mastermind 36756 points

    Hi Brian,

    The TPS65987D can only be powered from VBUS when operating as a Sink. If you need the TPS65987D to be a Source, VIN_3V3 must be provided. If you will only ever operate as a Sink, you leave VIN_3V3 as no connect (refer to TIDA-050014 for Sink Only reference)

    The Over current protection is only valid when operating as a Power Source. We do not implement OCP when operating as a Sink. The USB PD spec requires that the Power Source has OCP. For Source applications, the Iocc is automatically selected based on the configuration setting for the PDO. Section 3.2.2 in the following app note describes that in more detail:

    If you need OCP for a Sink only application, it would need to be implemented externally.

    If this answers your question, PLEASE select This resolved my issue

    Thank you,
    Eric

  • 0 in reply to Eric Beljaars
    TI__Expert 4060 points

    Thanks, Eric. I have some additional questions I was hoping you could clarify.

    1. Since the controller is operating in standalone mode, I am not planning to use either of the I2C interfaces. Can the SCL and SDA pins be left as no connect?
    2. Correspondingly, can ADCIN2 be left as n/c since the I2C address does not need to be configured?
    3. For the device default configuration options available with boot mode pin strapping (Section 8.4 of datasheet), I do not see an option for DFP with sink 5-20V as an available option, especially with BP_NoWait (disabling dead battery mode).  Can you provide some guidance on what the default device configuration should be set to for dead battery mode disabled, PD configuration read from external flash, and default DFP with 5-20V at 0.9-3A Sink capability.

    Thanks,

    Brian Angiel

  • 0 in reply to Brian Angiel
    TI__Mastermind 36756 points

    Hi Brian,

    1. I would strongly recommend to leave pull-ups to LDO_3V3 on at least one of the I2C interfaces. This would greatly simplify bringup and debug as you could access all of the registers through out GUI tool.

    2. ADCIN2 can be tied to GND to prevent any strange behaviors from floating an ADC input

    3. BP_NoWait would be the correct configuration for this. BP_NoWait doesn't wait for VIN_3V3 to become high and will instead immediately load the configuration from the SPI-Flash when VBUS becomes active as a sink. If they never want to boot from VBUS and only want to boot when VIN_3V3 goes high, then BP_NoResponse would be the correct config.

    If this answers your question, PLEASE select This resolved my issue

    Thank you,
    Eric