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TPS65218 How to configure unused DCDC

Rene Straub
Prodigy 120 points
Other Parts Discussed in Thread: TPS65218

Hello TI & Forum,


we are working an a AM335x design, powered by a TPS65218. In this design DCDC2 of the TPS65218 is not used/required. I understand that DCDC2 is part of the power sequencing and requires a valid voltage to allow PGOOD to assert.

  • What is the minimal circuit required to make the TPS65218 sequencer see a valid voltage on DCDC2?
  • Can I connect the output of DCDC1 to FB2, let L2 open and ground IN_DCDC2.

Best regards

-Rene

  • 0
    TI__Intellectual 1990 points

    Hi Rene,

    Thank you for the post. That is correct, DCDC2 is a part of the power up sequence and needs to be tied to a valid voltage. Are you planning on dynamically scaling DCDC1 output voltage? What voltage will DCDC3 be set to? If you plan on using dynamic voltage scaling for DCDC1 and strict=0 in reg 0x13h, I would tie FB2 to FB3 and leave L2 floating. IN_DCDC2 needs to be connected to the same input voltage as IN_BIAS. This allows the internal PGOOD circuitry of DCDC2 to operate to determine if the output voltage on DCDC2 has a valid voltage or not. If dynamic voltage scaling will not be used on DCDC1 and strict=0 in reg 0x13h, then you can tie FB2 to FB1 and leave L2 floating. IN_DCDC2 should be connected to the same input voltage as IN_BIAS.

    If strict=1 setting is used, there may not be a way to connect an unused converter. Let me know which strict setting you are planning on using.

    Let me know if there are any questions. Thanks!

    Regards,

    Paul Kundmueller

  • 0 in reply to Paul Kundmueller
    Prodigy 120 points
    Hello Paul,

    thanks for the quick answer. I plan to have DCDC1 on 1.1V (Core Supply). DCDC3 is configured for 1.5V DDR3 Supply.

    Currently voltage scaling is not used, but I guess this could become an option (lowering clock, reducing voltage). Since this will only be used from the Linux OS, I guess this is not a problem. We plan to disable DCDC2 from the bootloader.

    Regarding the Strict Mode we are open. Currently strict=0 is used. Again I think this should not be a problem, once DCDC2 is disabled by software.

    Can you confirm that DCDC2 will not influence PGOOD when disabled.

    Best regards
    -Rene
  • 0 in reply to Rene Straub
    TI__Intellectual 1990 points

    Hi Rene,

    That is correct, DCDC2 will NOT influence PGOOD when disabled. Let me know if there are any other questions. Thanks!

    Regards,

    Paul Kundmueller

  • 0 in reply to Paul Kundmueller
    TI__Intellectual 1990 points

    Hi Rene,

    Sorry I forgot to add, if DCDC2 is disabled and TPS65218 is still active, there will be some current draw from the internal active discharge on DCDC2 (see excerpt from datasheet). If DCDC1 is tied to the unused, disabled DCDC2, then you can expect a MAX current draw of 8mA (1.2V / 150ohm). Let me know if you have any questions. Thanks!

    Regards,

    Paul Kundmueller

  • 0 in reply to Paul Kundmueller
    TI__Intellectual 1990 points
    Hello Renee,

    One more note, DCDC2 (1.1V) needs to be connected to a voltage higher than DCDC1 (1.1V). This will prevent any erroneous switching if DCDC1's operating point is slightly lower than DCDC2's operating point at start up when DCDC2 is still enabled. I would recommend tying DCDC2 to DCDC3 (1.5V) in your case. Let me know if you have any questions. Thanks!

    Regards,

    Paul Kundmueller