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TPS65094: Power supply scheme

Umberto Frangi
Expert 4045 points
Part Number: TPS65094
Other Parts Discussed in Thread: TPS650864, LM2767, TPS61040

Hi,

 I have the following question:

-if you have on the board a stable 5V can you use to power both the device thru DRV5_1_6 and the external mosfets?

-or do we need to use Vsys for external mosfets?

-what is the function of Vsys if you can power everything at 5V?

In the datasheet there are diagrams with Vsys=4.5V, that is below the min voltage.

Thanks

Umberto

  • 0
    TI__Genius 9310 points
    Umberto,
    The Vsys has a minimum operating voltage of 5.6V. I have looked through all of the diagrams and can't find a place where Vsys refers to 4.5V. Please identify the diagrams in the data sheet where you see this reference. This could be a mistake and needs to be corrected if it does.

    The TPS65094 produces LDO5 to feed the Bucks and LDO's internal controls. This voltage appears on DRV5_1_6 to be filtered. You can't supply an external 5V to this pin as the LDO5 regulator will compete with an external regulator. The high current for the Bucks comes from Vsys. The control section that drives the mosfets is modulating the mosfets based on the Vsys voltage and the feedback voltage not the LDO5 voltage.

    The internal control structure runs from the Vsys, you can't bypass this input voltage.

    I hope this answers your questions. Let me know if you need more information.
  • 0 in reply to Gordon Varney
    TI__Expert 4045 points
    Hi Gordon,
    see efficiency diagrams at page 27 of datasheet with Vsys= 4.5V,5V,5.5V.
    The customer I was talking to claims he saw a solution where the board has 5V as general input that is supplied also to external mosfet; then Vsys is generated with a small boost from 5V.
    This does not seem in line with your suggestions.
    If a customer has only a 5V input ,then he needs to boost it at >5.6V for Vsys but with high current output
    Thanks
    Umberto
  • 0 in reply to Umberto Frangi
    TI__Genius 17380 points

    Hi Umberto,

    Thank you for pointing this out, I have taken an action to update those efficiency plots to say PVIN rather than VSYS.

    It is possible to use an external boost to power the TPS65094 family's VSYS pin. The applications section of the TPS650864 datasheet includes a section regarding how to implement this. The VSYS pin is mainly used to power the digital which is low power and to monitor that the VSYS voltage is not below 5.4 V (minimum battery voltage on a 2S battery system). We have seen minimal impact using 5V to power the controllers (BUCK1, BUCK2, and BUCK6) from 5V with VSYS pin held at 5.8V. With VSYS held at 10V (using a voltage doubler), the controller switching frequency will increase to ~1.6 MHz. This isn't a bad thing, it's just a side-effect of having mismatched VSYS pin and FET input voltage. The LM2767 is the more popular solution with low cost applications, the TPS61040 is more popular with more conservative designs.

    One more note is that the DRV5_x_x pins can be powered directly from an external 5V supply. They typically come from LDO5P0 in a normal system because the LDO5P0 output acts as a power path between the less efficient VSYS powered LDO5 and the more efficient externally supplied V5ANA and allows the controllers to be enabled whether the external 5V is there or not. In this case, the 5V will always be present if PMIC is enabled, so the LDO5P0-to-V5ANA load switch can be bypassed.

    There is a note on designing ATX based systems which is partially relevant:
    https://e2e.ti.com/support/power-management/f/196/t/713125