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AM3892 Pin connections, unused USB Pins and DDR power pins

Jimmy Fung
Intellectual 575 points
Other Parts Discussed in Thread: AM3892

We are designing with the AM3892 and had a few questions on the pin connections that we could not find answers to in the datasheets.

1) We are not using USB interface should we keep pins T29, R29, T30 and R30 unconnected? The manual doesn't say anything about what to do with those power pins in such case.  Should I tie them high and if so, with what value resistor?

2) AM3892 manual says that pins N27 (VDD_USB_0V9) could be connected to 0.9V or CVDDC (1.0V). But the proper power up sequence enable 1.0V power supply before 0.9V power supply. We are wondering if there is any risk that even not used USB PHY but power up in not recommended order might cause latch up problems? The proper power up sequence is: 3.3V, 1.0v_AVS, 1.0V, 1.8V, 1.5V and 0.9V.

3) Do we need to power up DVDD_DDR1 power pins with 1.5V if the second for DDR[1] will not be used?

  • 0
    TI__Mastermind 25055 points

    Hello,

    For all use cases (even when the USB interface is not used) the 3.3v, 1.8v and 0.9v supplies need to be connected. Only if the USB PHY is not used, then the 0.9v and 1.8v pins can be optionally connected to CVDDC (1v constant) supply while the 3.3v pins need to be connected to a 3.3v supply.  I will make sure the 3.3V pins get updated in the datasheet with this information.

    If USB is not used then the 0.9v pin can be connected to 0.9 V or CVDDC and the power sequence will be OK.  If USB is used then 0.9V must come after the 1V constant supply.

    DDR1 power pins should still be connected.

    Regards,
    Marc