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TPS659037: Powering TPS6590379 with 3.8V supply

Kazuki Itoh
Genius 9595 points
Part Number: TPS659037

Hi team,

My customer is designing the system with AM5746ABZXA + TPS6590379ZWSR solution.

They don't use USB, so the system doesn't have VBUS and +5V.
So, my customer wants to power LDOUSB_IN1/2 with +3.8V for PMIC.
However, the datasheet recommended operating conditions for LDOUSB_IN2 is >4.3V.

Is it allowed to connect +3.8V to LDOUSB_IN2?

If it is not allowed to input +3.8V to LDOUSB_IN2, how should this pin be terminated?

Best regards,
Itoh

  • +1
    TI__Mastermind 38550 points

    Hi Itoh,

      LDOUSB has 2 optional inputs. In the case you mentioned, LDOUSB_IN1 should be used for the LDOUSB input by setting the bit "LDOUSB_ON_VBUS_VSYS=1" in the LDO_CTRL register (Physical address 0x16A).

    Thanks!

    Phil

  • 0 in reply to Phil Yi40
    TI__Genius 9595 points

    Hi Phil-san,

    Do you mean LDOUSB_IN2 can be left floating in that case? How should I terminate the LDOUSB_IN2?

    Regards,

    Itoh

  • +1 in reply to Kazuki Itoh
    TI__Mastermind 38550 points

    Hi Itoh-san,

      It's better to connect LDOUSB_IN2 pin to GND since it's an analog input. 

    Thanks!

    Phil

  • 0 in reply to Phil Yi40
    TI__Genius 9595 points

    Hi Phil-san,

    According to TPS659037 TRM, LDO_CTRL register is undetermined when this register is reset.

    In the case 3.8V is connected to LDOUSB_IN1 and LDOUSB_IN2 is connected to GND in the initial condition, is it going to be undetermined whether LDOUSB_OUT will be IN1 or IN2?
    My customer was assuming that LDOUSB_IN1/2 input sequence will be reflected to this register.
    Is there any other approach to make LDOUSB_ON_VBUS_VSYS=1 without the register setting?

    Also, if LDOUSB_OUT is unused and LDOUSB_IN1/2 = GND, will LDOUSB_OUT be GND level?
    My customer will disable USB PHY by AM5764 in this case.

    Regards,
    Itoh

  • +1 in reply to Kazuki Itoh
    TI__Mastermind 38550 points

    Hi Itoh-san,

      If customer disable the USB PHY by AM5764, then LDOUSB_IN1/2 should be connected to GND, and then LDOUSB_OUT be floating and close to GND level. 

    Thanks!

    Phil

  • 0 in reply to Phil Yi40
    TI__Genius 9595 points

    Hi Phil-san,

    Could you please address my first question as well?

    According to TPS659037 TRM, LDO_CTRL register is undetermined when this register is reset.

    In the case 3.8V is connected to LDOUSB_IN1 and LDOUSB_IN2 is connected to GND in the initial condition, is it going to be undetermined whether LDOUSB_OUT will be IN1 or IN2?
    My customer was assuming that LDOUSB_IN1/2 input sequence will be reflected to this register.
    Is there any other approach to make LDOUSB_ON_VBUS_VSYS=1 without the register setting?

    Regards,

    Itoh

  • +1 in reply to Kazuki Itoh
    TI__Mastermind 38550 points

    Hi Itoh-san,

      From register default setting as "x", it's undetermined whether LDOUSB_OUT will be IN1 or IN2.

     There is no other way to make LDOUSB_ON_VBUS_VSYS=1 without the register setting.

    Thanks!

    Phil