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TPS65920 power up, boot mode

John F.
Intellectual 830 points
Other Parts Discussed in Thread: TPS65920, OMAP3530

We have a custom OMAP3530 board with a TPS65920 with boot0 tied high to 3.3V and boot1 is not connected which according to manual should be low (through internal pulldown).  We have 3 boards all of which have VIO =1.8V, but VDD1 and VDD2 do not power up.

We noticed that on the OMAP3530 EVM (of course, different power chip) both boot0 and boot1 are tied high.  Is this boot mode documented for the TWL4030?  Is this a valid mode for the TPS65920?

 

Is this connection of resistors correct for OMAP3 boot mode?  The value of boot1 seems to float between 0.8->1.1V which doesn't seem right.

 

Thanks,

John

  • 0
    TI__Prodigy 630 points

    Hi John,

          Boot0 and Boot1 both HIGH indicate Slave mode. For OMAP3 Master mode, Boot0 must be HIGH and Boot1 must be LOW. Boot1 floating to such a value is not correct. Please tie it LOW. It could solve your issue.

    Could you give the reference where you see that there is an internal pull down on Boot1?

    Regards,

    Kartik

  • 0 in reply to Kartik Sudarshana11777
    Intellectual 830 points

    Hi Kartik,

    Table 2-2 in the TPS65920 June 2009 version shows that Boot0 and Boot1 both have internal pull down resistors, so the assumption was that any additional external pulldown would not be required.

     

    We tried tying Boot1 to ground, but still had trouble with VDD2 not coming up.  About 7ms after VIO ramps up (should be 1.179ms according to section 4.4.3.2?), VPLL ramps quickly to 2.8V (the deafult in the spec is 1.8V?), then VDD2 starts slowly ramping, but never makes it, then decays back to zero V.  It makes me wonder if the TPS determines after a certain time (due to external loading?) that VDD2 will not ramp normally, so it must be shut down.  We're wondering if the 3530 CPU has been damaged during testing and is causing the TPS to not start up.

     

    By the way, is there a more detailed description of MC027 boot mode (boot0=0 boot1=1) whic is listed in the June'09 manual?

     

    Thanks,

    John

  • 0 in reply to John F.
    TI__Genius 15100 points

    Hi John,

    You should be using MC021 for OMAP3 master mode. MC027 is for OMAP2. The power-up sequence differs for these two modes.

    You can check the following few posts on this forum, your problem may be similar to these.

    http://community.ti.com/forums/p/8502/32927.aspx#32927

    http://community.ti.com/forums/p/3648/13285.aspx#13285

    Do you see VDD1 and VDD2 toggle or they simply try to rise and then go to zero. If you have a layout issue, generally you see the voltage levels on the DCDC toggle.

    Let me know if the above posts help.

     

    Regards,

    Gandhar.

     

  • 0 in reply to Gandhar Dighe
    Intellectual 830 points

    Hi Gandhar,

    We tried MC021 mode on another board which apparently was not damaged, and all supplies came up OK.

    Thanks for your help!

    ,

    John