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TPS65381-Q1: If the IGN signal is switched on at the same time as 12V supply, will the system fail to start up?

Kun Yuan
Intellectual 945 points
Part Number: TPS65381-Q1
Other Parts Discussed in Thread: TPS65381A-Q1

Hi E2E,

This is my first time to use the TPS65381 and TMS 570. I  meet a problem with TPS65381-Q1 and TMS570. I was doing functional test on the board , I found that the system will failed to start up if IGN signal is switched on at the same time as 12V power supply. I studied the data sheet of TPS65381.I have been confused about the discription of " Power-Up and Power-Down Behavior ".

1st. If the IGN signal is lasted high before the start-put of VBATP + 12 V  and be pulled down before the end of ACTIVE STATE,  the system will be failed to start up and stepp in STANDBY STATE, even the Device State step in STANDBY STATE again?  Or the IGN signal could start up the system in more chance?

2nd. If the IGN signal is  high before the start-up of  VBATP + 12 V  and lasted high before the end of ACTIVE STATE, the system will be successed ?

In summary, is there a problem with on-grid timing? If the system fail to start up, I need to use the MCU to clears IGN_PWRL bit?

  • 0
    TI__Mastermind 20590 points

    Hi Ku

    Using the main power supply as the signal for IGN is fine and should work.  As long as IGN pin input level is > 3V (POS 7.1, IGN_WUP, threshold) and the VBAT supplies, VBATP and VBAT_SAFING, have crossed above 5.8V input (minimum to start up the device), the device should wake up and start up. Many non automotive and even automotive systems have been design this way with the TPS65381A-Q1.  

    Once IGN goes low the device will power off if IGN is used as the wake up source.  Think of it as a combination that on power up when VBAT supply pins are above 5.8V and IGN is above IGN_WUP threshold the device will power up.  At any point there after if IGN goes below the IGN_WUP threshold, the TPS65381A-Q1 will power off and go to STANDBY state.  If VBAT supply pins are low at any point the device will be below its power on threshold and not power up.

    If IGN is high before the supplies powers up, the device will still power up when the VBAT supply pins rise above the power on threshold.

    Using IGN_PWRL is really for in system programming of the MCU (flashing) not to with the power up down of the device.

    Please ensure you have adequate supply voltage and current to the supply pins, VBATP and VBAT_SAFING which IGN pin is high.

    Scott

  • 0 in reply to Scott Monroe
    Intellectual 945 points
    Hi Scott! I think there are some misunderstand between my discription and your understand. The detail is as follow:
    1st. My system is not connected 12V power, and there is no IGN signal.
    2nd. Normally, the TPS65381 is connected to the 12V battery, which can provide power to system. But when I do the test on the product, the relays of test kit is only one. So the product is not connected to the 12V power at first and I use on relays to link the 12V and IGN to the system.
    3rd.When I press the key to activate the IGN signal , the 12V power is provided to the system at the same time with the IGN signal. So , I want to know is there a power up timing to influence the normal work ?
  • 0 in reply to Kun Yuan
    TI__Mastermind 20590 points

    Hi Kun,

    there is no timing dependency for start up.  Wake up or power up is dependent on an AND function of the voltage levels on both the supply and IGN pin. 

     As long as IGN pin input level is > 3V (POS 7.1, IGN_WUP, threshold) AND the VBAT supplies, VBATP and VBAT_SAFING, have crossed above 5.8V input (minimum to start up the device), the device should wake up and start up.

    Best Regards,

    Scott

  • 0 in reply to Scott Monroe
    Intellectual 945 points
    Hi Scott!
    Can I understand that even if the first start failed, I don't need to use the MCU to clears IGN_PWRL bit. As long as IGN pin input level is > 3V and the 12V power supplies, the device will wake up and start up ?

    Best Regards,
    Kun
  • 0 in reply to Scott Monroe
    Intellectual 945 points
    Hi Scott! I also want to ask that the 12V power has nothing fluence with the IGN. If the IGN signal comes before the 12V supply, the system will fails to start up. Just need to wait 12V power supply ,and the system will start up if the IGN signal comes again and its voltage level > 3V . Am I right?
  • 0 in reply to Kun Yuan
    TI__Mastermind 20590 points

    Hello Kun,

    Correct,  when IGN pin is > 3V and VBATP and VBAT_SAFING supply pins have proper voltage on them to start up or have crossed the start up voltage level when IGN pin is at a high level the device will be in a power up state.

    The IGN_PWRL latch is an optional feature to latch the IGN signal high so the device will not automatically power down to STANDBY state when IGN pin transitions to a low level (< 2V).

    Best Regards,

    Scott