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TPS65982-EVM and option of a single converter for 5V and 12V

John Melinyshyn
Prodigy 10 points
Other Parts Discussed in Thread: TPS65982, TPS65982-EVM

The TPS65982-EVM uses two separate DC/DC converters for 5V and 12V.  I am investigating  if a single DC/DC converter can be used to provide both 5V and 12V for the TPS65982 to reduce cost and component count in a production design.

I am posting in this forum because it's not clear if the TPS65982-EVM is using two separate DC/DC converters to support timing requirements of USB PD or if it was only done to make the EVM design more straight-forward.

Q1:  Does the TPS65982-EVM need two separate DC/DC converters (5V and 12V)  to support USB PD requirements?

Q2:  If the answer to Q1 is "no", is it practical to use a single device like the TPS54335 and switch between 5V and 12V by just switching the VSENSE resistor network?

Thank you.

  • 0
    TI__Prodigy 735 points

    Hi John,

    I've contacted the factory expert that is responsible for the TPS65982-EVM.  Please expect a reply shortly.

    Thanks,

    Fabio

  • 0
    TI__Mastermind 30310 points

    John,

    Page 30 of the TPS65982-EVM User's Guide shows the power circuitry for the EVM. The DC Barrel Jack, which plugs in at J9, provides 20V which is connected directly to the high side of RSENSE (R1) when jumper J6 is installed. This node is commonly referred to as PP_EXT, which feeds into the External High Voltage (HV) FET path.

    The ICs labeled U6 & U7 are both TPS4335 DC-DC converters that generate 5V for PP_CABLE and PP_5V0 and 12V for PP_HV. As you pointed out, this design makes the EVM simpler and more straightforward, but it definitely does not make it cheaper. In complex 2 port designs, it is possible for U6 to feed 5V into PP_5V0 of both ports while U7 can feed 12V into PP_HV of both ports. In this type of design, 2 DC-DCs is the minimum, so it would be the simplest AND the cheapest.

    Q1 Answer: No.

    Using 2 DC-DCs is not needed to meet timing for USB-PD, but because the TPS65982 controls the Rise and Fall time of VBUS and provides excellent reverse current protection, it definitely makes it easy to meet timing requirements when switching from stable 5V to stable 12V.

    Q2 Answer: Yes, you are a clever and frugal designer. The TPS4335 could be used to switch between 5V and 12V by switching in/out a single R2 sense resistor.

    The TPS65982-CONFIG FW Config-Tool easily lets you modify the default FW image to match your new HW settings. These are some of the selections you will need that are different than the "Load Defaults" 

    He are some HW guidelines you may want to think about:

    • PP_CABLE: You will still need to provide up to 500mA on PP_CABLE, so you will need to disconnect PP_CABLE from PP_5V0 and use a 2nd (cheaper) DC-DC to generate 5V (the TPS65982 limits at 600mA to account for a little overhead)
    • 12V-5V Transition: The only timing concern you will have is "bleeding" the voltage down to 5V after a 12V contract has been interrupted by a PD Hard Reset or ended via un-plugging the Type-C connector.
    • A GPIO Event can be used for this also, but Source PDO0 Event will not bleed current on an un-plug event (I will see if there is an ideal event to use)
    • R2B (VREF) Driver Ckt: When we tested a design like this in the lab (Direct Variable AC-DC Converter), we replaced a BJT with a low Rds-on, lower power NMOS FET, ripped off an LED and blue-wired R2B to  the High-side of the NFET. It worked like a charm!

    Hope this helps you get started! Please follow-up here if you get stuck again.