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Why my am335x is often damaged?

zuobing huang
Intellectual 300 points

The am335x power on Power-Up Sequencing: 1.8V, 3.3V, 1.1V. When the device is Power-Up, the RXD of the uart will input the power (3.3V) to the am335x.So when the 1.8V is power on，the 3.3v of the am335x will have 1.0v.

  • 0
    TI__Guru**** 393215 points
    Power supplies to external components must ramp-up after the AM335X power supplies.
  • 0 in reply to Biser Gatchev-XID
    Intellectual 300 points

    When my system have many board , one board have an am335x and a power system? One board have communications to the other board. I can not ensure"Power supplies to external components must ramp-up after the Am335x power supplies."

  • 0 in reply to zuobing huang
    TI__Guru**** 393215 points
    To be more precise, the peripheral power should ramp-up at the same time as the VDDSHVx power supply.
  • 0 in reply to Biser Gatchev-XID
    TI__Guru**** 393215 points
    Huang,
     
    Since you mention that this is an UART_RXD pin that's causing the problem, a possible workaround is to place a diode on this line (anode on AM335X side). Then you will also need an external pullup resistor to VDDSHVx between the diode and AM335X, or you can enable the internal pullup for this pin. I would recommend using a Schottky diode because of the fast response and small voltage drop.
  • 0 in reply to Biser Gatchev-XID
    TI__Guru 64655 points

    There is a good chance your system will violate the AM335x Absolute Maximum Ratings parameter "Steady State Max. Voltage at all IO pins" if you do not properly sequence your power supplies.

    There is also a chance you will violate a similar parameter for the peripheral devices attached to AM335x since most CMOS devices have a similar limit.  In a few cases, devices may be designed with fail-safe inputs which allow voltage to be applied to the input while the device is powered off.

    This is one of the small design details that is commonly over-looked, but power sequencing of all devices in a system should be considered when designing your product.

    In some cases, it may be necessary to put isolation circuits that disconnect devices while power is sequenced

    Regards,
    Paul

  • 0 in reply to peaves
    Intellectual 300 points

    I move the other board from the system,  the Power-Up Sequencing and Power-Down Sequencing is a above.

    Are three any problems?

    ALL the below 1.1V of the am335x are connect together.

    ALL the below 1.8V of the am335x are connect together.

    ALL the below 3.3 of the am335x are connect together.

    vdd_core 1.1

    vdd_mpu 1.1

    vdds_pll_mpu 1.8

    vdds_sram_mpu_bb 1.8

    vdds_sram_core_bg 1.8

    vdda3p3v_usb0 vdda3p3v_usb1: 3.3

    vdda1p8v_usb0 vdda1p8v_usb0:1.8

    vdds_pll_ddr 1.8

    vdds_ddr 1.8

    vddshvx 3.3

    vdds 1.8

    vdda_adc : 10k to gnd

    vdds_adc gnd

    vpp: no connect

    vdds_pll_core_lcd 1.8

    vdds_rtc 1.8

    cap_vdd_rtc 1.1

    RTC_KALDO_ENn:10k to 1.8

    VDDS_OSC: 1.8 

  • 0 in reply to zuobing huang
    TI__Guru**** 393215 points
    Hi Huang,
     
    Everything looks fine here.