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TPS65073 Converters Power Up

Andrew Rankin
Prodigy 40 points
Other Parts Discussed in Thread: OMAP3530, TPS65073

Hello there, I am currently working on an application using the TPS65073 to power an OMAP3530. The application will use a battery that will be charged via USB only. There is no power on/off button, so the device would be required to power up with USB input or by the battery without USB input. However, I would like to clarify operation of the device in two situations, in particular the setting of PB_IN.

The datasheet states that in this type of application when powered from BAT, PB_IN would need to be tied low to enable power up of the converters when POWER_ON is released. For this, I was planning on connecting PB_IN directly to 0V. However, it also states that if the device is powered from USB (and not BAT), PB_IN must not be tied low to start up the converters.

  1. If the battery is discharged and power is input at USB, will the device power up if PB_IN is held low ?
  2. What set-up would be required to allow the converters to operate from USB when input and BAT otherwise, considering there is no control over PB_IN?

Many Thanks for your input.

Andrew.

  • 0
    TI__Expert 6060 points

    Please have a look at page 34 figure 33 of the TPS65073 datasheet.

    Figure 33 shows the state diagram of the TPS65073.

    There is a difference if the device is powered from

    - AC / USB

    - BAT

    1) In case device is powered from AC/USB

        As soon as input voltage is applied to AC or USB the device will transition in POWER_ON (SYS = ON) mode - ramping up the SYS output voltage (output of the Power Path).

    The converter remain off in this state. Pulling /PB_IN low or pulling POWER_ON high will cause the DC/DC converters and LDO to ramp with their internal fixed power up seuqence (device transitions in POWER_ON1 state). Please note to keep the converters enabled POWER_ON must be pulled high ,before /PB_IN is released high again. Typ. /PB_IN is connected to an push button, while POWER_ON is controlled by the application processor. If there is no push button (ON/OFF switch in the system) POWER_ON can be directly conneced to SYS - this will cause the converters to start up after AC/USB supply is connected and SYS output voltage ramped up. Note to shut down the converters again in reversed power up seuqence POWER_ON needs to be pulled low again.

     

    2) In case device is supplied from BAT only.

    /PB_IN needs to be pulled low. Note that the device needs to detect the falling edge on /PB_IN ==> connecting /PB_IN directly to ground will not work.

    When /PB_IN is pulled low SYS output voltage ramps and the DC/DC converters and LDOs ramp up in their internal power up sequence. POWER_ON needs to be pulled high before /PB_IN is released high again to keep the converters enabled.

    Please find answers to your questions embedded below.

    1. If the battery is discharged and power is input at USB, will the device power up if PB_IN is held low ?

    Pulling /PB_IN static low will not work, since the device needs to detect the falling edge on /PB_IN. Anyway if the device is powered from USB - SYS will ramp up after USB is connected. The converters can be enabled by pulling POWER_ON high. Either control POWER_ON from external circuit of connect POWER_ON to SYS./PB_IN can be left floating (there is an internal pull-up resistor connected to the /PB_IN pin)

          2.       What set-up would be required to allow the converters to operate from USB when input and BAT otherwise, considering there is no control over PB_IN?

    See answer above

    Let me know if you have any further questions.

  • 0 in reply to ChristianHoefling
    Prodigy 40 points

    Many Thanks for the response.

    It appears that I'd need to leave /PB_IN floating and hook-up VSYS to POWER_ON to meet the requirement.