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TPS65983: How to change the TPS65983 positive voltage transitions slew rate

Picher Lu
Prodigy 160 points

Part Number: TPS65983

Hi，there

When I verify the type c PD controller TPS65983 source function, I found that the PP_EXT to VBUS positive voltage transitions slew rate is out of the specification on datasheet, and I don't know how to meet the spec according the datasheet, is there any method to change the slew rate for positive voltage transitions?

Below is the source function test record, slew rate=66666V/S

and spec on the datasheet, slew rate=30000V/S Max

Thanks,

Picher 

  • 0
    TI__Expert 4415 points
    Hi Picher,

    Welcome to E2E world.
    TPS65983 is used to build thunderbolt ecosystem ONLY, are you using for Thunderbolt? If not, then I would recommend TPS65981 which has all the features as TPS65983.
    From the picture, the slew rate is too high. Could you please tell the part number of the DC/DC and the MOSFET of the external power path? Because the slew rate of the DC/DC and parallel capacitance of the MOSFET might have an effect on the VBUS voltage transitions slew rate.

    Best Regards,
    Hao
  • 0 in reply to Hao Wang14
    Prodigy 160 points

    Hi Hao,

    Now I using TPS65983 to act as  USB PD Sources, Sinks, and Dual-Role Port application, I think TPS65983 can be able to do this.

    I use the DC power supply to supply the PP5V0 and PP_EXT, and it is always powered. The external MOSFET is CSD17527Q5A, and the MOSFET without external parallel capacitor, I know add an external parallel to MOSFET GS can improve the SR, but I don't think it's a good method.

    I also verify the TPS55982 EVM module from TI, the slew rate of PP_EXT to VBUS is also high like figure below, SR=15V/378uS=39682V/S

    I don't think the chip spec parameter is related to external device, are there any factors on chip like fireware etc. can help to configure the slew rate?

    Best Regards,

    Picher

  • 0 in reply to Picher Lu
    TI__Expert 4415 points

    Hi Picher,

    Unfortunately, TPS65982 cannot control the slew rate of the voltage transition.

    From your reply, it seems that you are using a single DC/DC to get all the voltages on PP_EXT, so we need to control the slew rate of the voltage transition when design the circuit. I don't know the part number of your DC/DC, if its switch frequency is too high, you should find a way to decrease the slew rate. Usually, we use GPIOs to get different output voltage shown in picture below. You could add a resistor and a capacitor to control the slew rate of the voltage transition on PP_EXT.

    If it solves your problem, PLEASE select  This resolved my issue  

    Best Regards,

    Hao

  • 0 in reply to Hao Wang14
    Prodigy 160 points

    Hi Hao

    I mean I did not use a DC/DC power supply, I was used the laboratory DC power supply, you can consider as the PP_EXT always have voltage on, for example it's always 20V, so I can't change the slew rate according PP_EXT input. Maybe I can only  get the desired SR with doing something with the VBUS, Maybe add an external MOSFET to VBUS and control it by GPIO, is that right?

    Thank you for your help.

     

    Best Regards,

    Picher

  • 0 in reply to Hao Wang14
    Prodigy 160 points

    Hi Hao,

    Does TI have similar products like TPS65982 which can control the slew rate of the voltage transition?

    Best Regards,

    Picher

  • 0 in reply to Picher Lu
    TI__Expert 4415 points

    Hi Picher,

    Do you mean that you use PP_5V0 as the source for 5V and connect the laboratory DC power supply to PP_EXT? If so, the voltage transition is from PP_5V0 to PP_EXT. You can choose the MOSFET with high Qgs which might help.

    In the actual application, the voltage of DC/DC is controlled by GPIOs which can change the value of the divider resistors. The positive voltage transition requirement is for the whole system.

    If you are not building a Thunderbolt ecosystem, I would suggest using TPS65981, here is the voltage transition for PP_EXT that I tested on TPS65981EVM, the slew rate is within the spec.

    I hope it helps and solves your problem, PLEASE select  This resolved my issue 

    Best Regards,

    Hao

  • 0 in reply to Hao Wang14
    Prodigy 160 points

    Hi Hao,

    Does the TPS65981 can configure the slew rate internal or need to select a suitable external MOSFET for meeting the specification?

    Thank and Best Regards,

    Picher

  • 0 in reply to Picher Lu
    TI__Expert 4415 points
    Hi Picher,

    Unfortunately, TPS65981 cannot control the slew rate. You are right, we can select the suitable MOSFETs and DC/DC if you are planing to build your own board. If you have further question, I would suggest posting here for further discussion.

    Best Regards,
    Hao
  • 0 in reply to Hao Wang14
    Prodigy 160 points

    Hi Hao

    Thanks for your help again, I would come here to discuss if I have other questions about  PD controller.

    Best Regards,

    Picherlu