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Device behavior under Slow VBAT ramp-up/down

Kummi
Mastermind 6220 points
Other Parts Discussed in Thread: TPS65381-Q1

Hi,

This is about the device behavior under Slow VBAT ramp-up/down.
Currently our application uses TPS65381-Q1 with TMS570LS071x.

We found an application report (SLVA643) which mentions the device
behavior with slow ramp-down/up conditions, but we couldn't understand
what measures should be taken for the Slow VBAT conditions.
Is it necessary to consider Voltage Supervisor IC for VBAT?

This E2E mentions that "if this rising edge is slow, i.e. 300ms, the TPS device will release
the reset before VBAT gets to 5.8V (the min voltage to operate for TPS65381),
and then cause a TPS65381 BIST test failure. Eventually, you will find your
TPS device staying in safe state."

What should be done if the device goes into the Safe state? please let us
know the procedure to change the device from Safe state to Reset or standby state.

Best Regards
Kummi

  • 0
    TI__Guru 68920 points
    Hi Kummi,

    I think this question is mainly about the TPS65381 so I'm going to move it to the automotive forum
  • 0
    TI__Mastermind 20590 points
    The slow VBAT ramp-up/down scenario applies to the main supply for the TPS65381. A slow ramp up or down on the VBAT supply to the device (VBATP and VBAT_Safing) may cause the VDD3/5 output voltage to droop as explained in the application note. If this occurs the TPS65381 will pull NRES (resetting any attached MCU) and will transition the TPS65381 through the RESET state. The internal supervisors detect this condition as outlined in the app note, no external circuitry is needed. The app note is to explain under abnormal supply conditions why RESET may be seen. The only other warning is not to have the input capacitance on the system so large that it would cause these extremely slow ramp up of the supply to the TPS65381.

    The link to the E2E you refer to goes to the MCU team E2E and is a different topic. It is how to wake up or power up the TPS65381 by tying the IGN pin to VBAT (supply) with a resistor. The TPS65381 will not release it internal power on reset until the voltage levels on VBATP, VBAT_Safing are met. There is no race of IGN and VBAT to start power up sequence as implied in that E2E response. Using IGN tie to protected supply (VBATP) is the normal way to use the TPS65381 if an external wake up signal like IGN or CANWU is not going to be used but the main supply to the device will be powered on or off. That post on the MCU forum doesn't understands the internal reset and power up requirements for the TPS65381. Even if IGN is above its thresholds, but VBATP and VBAT_Safing are below their power up levels the TPS65381 will not try to start up and thus BIST wouldn't run and fail causing a transition to SAFE in this scenario. The statement from that E2E post is not correct: "if this rising edge is slow, i.e. 300ms, the TPS device will release the reset before VBAT gets to 5.8V (the min voltage to operate for TPS65381), and then cause a TPS65381 BIST test failure. Eventually, you will find your TPS device staying in safe state." for the scenario it is describing used with TPS65381.

    Best Regards,
    Scott