• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 99 subscribers
  • Views 1059 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

AM5728: Power sequencing violation causes overheating

Rogerio Almeida
Mastermind 26205 points
Part Number: AM5728

From field:

Customer recently found AM5728 is overheating when the power sequence violation. Figure 1 is the diagram of power supply. In order to fix overshoot issue, they slow the switch time of mosfet, which makes the arrival time of ps3v3 and reset voltage is similar. Please refer to ‘ps3v3-vsdmmc-pmic_rst_out_vcc_3v3-02 (2)’. Than they observed the overheat of AM5728, about 100 degree Celsius, and normal tem is 60-70 degree Celsius.

 

They doubted that the violation of power sequence results in latch up of AM5728, which leads to high currents and device damage. And they hope they can get an official confirm of their doubt. Thank you.

 

 

  • 0
    TI__Mastermind 26205 points

    For some reason the figure one was not there..adding it here

  • 0
    TI__Genius 13567 points
    They will need to delay the PMIC_RESET_OUT signal to avoid damage. But if the PMIC solution is being used then there should be no sequencing violations? Is there more info on why the sequencing is different?
  • 0 in reply to Ahmad_Rashed
    TI__Mastermind 26205 points
    Thanks Ahmad
    I will let field post the details, I sent them the link to this post
  • 0 in reply to Ahmad_Rashed
    TI__Intellectual 1780 points

    Hello, here are some details.

    They did two experiments. 

    Figure1 below is PS3V3 and VCC3V3 I/O voltage circuits, where the VCC3V3_ON signal comes from the output ON signal of PMIC.

    Figure 2 is normal operation mode Yellow signal: VCC3V3 is I/O voltage, red signal: PMIC output Reset 

    Figure3 But sometimes they found there will be undershoot due to MOSFET. So they add a 10uF capacitor between pin 3 and pin4 of AO4409 shown in Fig. 1. MOSFET starts slowly. The maximum down voltage of PS3V 3 is 3.1V. PMIC does not restart.

    But VCC3V 3 and Reset start simultaneously. In this case, AM5728 is over 100 degree Celsius.

    What is the internal mechanism of AM5728 overheating?

    Thanks.

  • 0 in reply to Jeff Xie
    TI__Genius 13567 points
    Asserting PORz is necessary for isolating the chip while supply voltages are ramping up or down. The dual voltage I/Os need to follow a certain power sequence before the PORz is released. This allows them to detect the supply voltage level and adjust to 1.8V or 3.3V operation. When the sequence is violated the I/Os can get damaged. Internal short-circuit due to improperly started I/O cells is likely the cause of the heat. If you can fix the sequencing and the heating remains then possible damage was caused.

    I'm also worried about the leakage seen on your vcc_3v3 rail. There is no known leakage on AM572x on that rail so this is coming from the board design.