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TPS65070: How to bypass power path?

David F.
Prodigy 195 points
Part Number: TPS65070
Other Parts Discussed in Thread: OMAP-L138,

I'm using TPS65070 for a new redesign that powers OMAP-L138 and Cyclone 4 FPGA.  The present design uses 5.4V input to the PMIC.  For my new design, I'd prefer to boost this voltage to 6.3V.  From the 65070 datasheet, the AC input max is 5.8V, but the VINDCDC input max is 6.3V.  I understand this is due to the overvoltage protection built into the power path controller.  I don't need or use the USB or BAT inputs (they have a capacitor to ground).

So can I bypass the power path controller, and feed 6.3V directly into VINDCDC(1,2,3)?

If so, what do I do with the various power path pins?  

Thank you!

David

  • 0
    TI__Expert 5600 points
    Hi David,

    Your question has been assigned for product expert.

    Best regards,
    Jari Niemelä
  • 0
    TI__Expert 8810 points
    David,
    You will need to supply power to one of the inputs - AC, USB or BAT. These inputs supply SYS which supplies the controller voltage. Then you can provide your 6.3V to VINDCDCx and VINLDOx inputs from your boost. Don't forget about the LED boost circuit. It will need power as well.
    I hope this answers your question. Let me know if you need more help.
  • 0 in reply to Gordon Varney
    Prodigy 195 points

    Gordon,

    Thank you for the reply.  From your message, it sounds like it's possible to do what I'm proposing.  But I don't think I understand all the details yet.  The max input voltage to AC input without overvoltage lockout is 5.8V, as between 5.8 and 6.3V the overvoltage circuit will enable.  Maybe I don't understand what happens when the overvoltage circuit kicks in.  What happens when the AC input exceeds the OVP threshold?

    I can't seem to find the answer to this question on the datasheet.  I see recommended VIN for "AC or USB pins" is 4.3 to 17V.  But recommended VIN for "AC or USB inputs, charger and power path active (no overvoltage lockout)" is 4.3 to 5.8V.  What's the difference?  Is the difference whether or not I'm using the battery charger?

    If you can straighten me out on these details, maybe I'll get it.

    Thanks!  I look forward to your quick reply.

    David

  • 0 in reply to David F.
    TI__Expert 8810 points
    David,
    I think your confusion is that the supply voltage to the AC, USB or BAT pin needs to ne a separate voltage input. example, put 5V on the USB to power the controller, then boost the 5V to 6.3V to run the DC-DC. This can change based on how you want to supply the IC power compared to how you want to supply the DC-DC power. You will end up needing two input supply voltages. Then just don't use the SYS voltage to power the DC-DC rails.
    You could use the SYS to drive the VINLDOx inputs and the 6.3V to run the VINDCDCx inputs. This would increase the efficiency of the LDO's.
  • 0 in reply to Gordon Varney
    Prodigy 195 points
    I think I understand your suggestion. My actual scenario is that I will have 6.3V main power. I will also have a 5V LDO for analog supplies. So I could run AC from my 5V LDO. But what about sequencing for power up and down? Could 6.3V VINDCDCx come up with or slightly before 5V AC? Or would I need to use a FET to switch on the VINDCDCx inputs? For instance, use a high-side FET between my main 6.3V and VINDCDC, and gate it based on the SYS output? Thanks.
  • 0 in reply to David F.
    TI__Expert 8810 points
    David,
    I need to change my earlier statement, as I just discovered that VINDCDC1/2 can't go above SYS, or it will damage the part. Using separate inputs will not be possible. It's confusing that VINDCDCx has a higher voltage rating, yet can't go above SYS.
    MY apologies as it was looking good. I don't see a way to bypass the power path feature for higher voltages.
  • 0 in reply to Gordon Varney
    Prodigy 195 points
    OK. So to finish the discussion, I still don't know what happens when the AC input exceeds the overvoltage threshold. Does it turn SYS off? Does it disable PGOOD? Does it trigger /INT? Does it enable /RESET?

    If SYS remains active (and it probably doesn't), maybe I could work around the status output bits.
  • 0 in reply to David F.
    TI__Expert 8810 points

    David,

      I know it's frustrating, but I will help as much as I can. I know the AC and USB inputs do not have overvoltage detection on the power path. There is however an overvoltage detection on the control circuits. OV will send the IC into POR. As for as the status of each pin, I can look that up for a power on reset, but I think that part should be easy.

      I am out all day tomorrow giving a lecture at a local university. If you want me to look up the status of the pins you mentioned, let me know and I can have that for you on Friday morning.