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TPS65070 power path

Nikolaus
Prodigy 10 points
Other Parts Discussed in Thread: TPS65070, OMAP-L138, TPS3805H33

3201.DevBoard.pdf

Hello,

 

Can you pls. clarify how to start up the TPS65070.

As far as I understand, according to the datasheet SLV950B, page 71 the power path of the TPS65070 should be enabled whenever there is a sufficient voltage on AC or USB regardless of the levels on PB_IN# or POWER_ON. The dcdc converters can be enabled later on by PB_IN# or POWER_ON. We don't use a battery and we don’t' use the wLED driver. Different from the attached schematic I connected bat to GND, reduced the resistor on TS to 1K and experimented with all possible combinations of PB_IN# and POWER_ON.

 

This is the setup I want to have, I need the sys voltage right after plugging in the USB or AC supply (there is no power on button, PB_IN# is open and should be pulled up internally) as I derive the supply voltage for the USB device controller from VSYS, later on after USB enumeration when the device is allowed to drain 500mA I would like to turn on the dcdc converters by bringing POWER_ON high from a GPIO of the USB device controller to power the remaining devices on the board.

 

However this does not work! the power path is not switched trough until I bring the POWER_ON high by an external voltage, not even pulling it up to SYS does the task.

 

Please tell me if the above behavior is intended or specify how it should be.

 

Nikolaus

 

  • 0
    TI__Expert 6060 points

    You are correct.

    In case AC or USB is used, SYS output voltage should ramp up as soon as AC/ USB voltage is applied.

    The converter can be enabled afterwards with falling edge and /PB_IN or pulling up POWER_ON && high level on /PB_IN.

    What is the SYS voltage you are seeing when you apply power?

    The problem could be that you have SYS loaded by an external load (LDOs in your schematic). Please note that SYS should not be loaded during start up.

    SYS voltage will be ramped up with a current limit ( V(AC/USB) / 500Ohm (typ) )until SYS reaches 1.8V.

    If you are drawing load current on SYS during start up that exceeds the soft start current limit SYS may not able to ramp up.

    Please try to disconnect any excternal load from SYS.

    In case you are not using a battery and you do not have a POWER switch, I would recommedn to leave /PB_IN floating (will be pulled high trough internal pull-up) and enable /disable converters with POWER_ON pin.

     

  • 0 in reply to ChristianHoefling
    Expert 1410 points

    Hello,

    I am reading the TPS65070 data sheet (SLVS950B of 12/2009) because I plan to use TSP65070 to power Omap-L138.

    As I understood from the data sheet - the output Power sequence (that includes dc-dc and LDOs) can start only with PB_IN# goes low.

    After that POWER_ON can go high (when PB_IN# is still low) to keep the system under the power. See page73 - Timing for OMAP-L138.

    As soon as POWER_ON asserted high (with PB_IN# = low) - PB_IN# became "don't care". PB_IN# can be toggled after that with no effect. Is this true?

    And another question:

    If PB_IN# goes low (to start power sequence) and then stays low forever (until power on AC input and SYS output is ON) - the signal POWER_ON is not even required. The output power supplies will stay ON util PB_IN# is low. Is this true? 

    I plan to use the voltage detection device (like TPS3805H33 with some inverter) to bring PB_IN# low after the power level on SYS output was raised to the required level.

    After that the voltage detection device output will stay = high and PB_IN# will = low until the power on SYS output exists.

    POWER_ON can be set high by the Omap-L138 any time when PB_IN# is low. 

    This system will stay "ON"  until power on AC input and SYS output is at the correct level.

    Is this true or I am missing something?

    Thank you,

    Boris Ruvinsky

    802-877-4978

     

     

     

     

  • 0 in reply to Boris Ruvinsky
    Expert 1410 points

    Hello,

    I continue reading the data sheet for TPS65070 and there is a state machine diagram on page34.

    State Machine can go to POWER_ON_1 state with condition PB_IN#=1&&POWER_ON=1. But the sequencing diagram on page73 did not reflect that.

    It looks like POWER_ON inpit with PB_IN#=1 can control the dc-dc and LDOs sequencing. PB_IN# can be puuled up forever.

    Just the description on page35 has some missprints: "Once this pin (POWER_ON) is pulled LOW while PB_IN#=LOW, the MPU is shutting down without delay"

    This must be read "when PB_IN#=HIGH". Is this correct?

    When you are reading the data sheet first time - any missprins are very confusing.

    Thank you,

    Boris Ruvinsky

    802-877-4978