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AM2754-Q1: Regarding pull up for MCU_RESETz

Bhavpreeta Charan
Expert 3445 points
Part Number: AM2754-Q1
Other Parts Discussed in Thread: SN74LVC3G17

Hello experts,

For the MCU_RESETz, refer to section 5.4 of the datasheet for DSP-side terminal processing.

The power supply is shown to be PU, but the same is not shown in EVM schematic. Do I need a PU?

image.png

  • 0
    TI__Expert 5300 points

    Hello Bhavpreeta Charan,

    Thank you for your query !

    According to the PROC190E1_SCH schematic, indeed there is No pull-up between the VCC_1P8_SYS and the AM2754-Q1 MCU_RESETz input. The R550 is DNI (missing).

      

    But there is a Schmitt trigger buffer SN74LVC3G17 between the warm reset button (DEBOUNCE_MCU_RESETz) and the AM2754 SoC MCU_RESETz input. The input of the Schmitt trigger pin 1 (1A) already has a pull-up resistor R615=10K attached to maintain the warm reset inactive HIGH level. This is sufficient to always drive the Schmitt trigger pin 7 (1Y) repeater output to a defined level within an acceptable range for the MCU_RESETz input.

    The Schmitt trigger has a push-pull output, not open drain, so it does not need pull-up to operate. On the other hand, I think there is no possibility for the MCU_RESETz input  floating in a Hi-Z state because the power supply VCC1V8_SYS is enabled a bit ahead of the MCU_RESETz IO rail power supply voltage VDDSHV_MCU. Therefore the MCU_RESETz is always actively driven by the Schmitt trigger output and the pull-up resistor is not mandatory.

        

    Pull-up not mandatory after schmitt trigger

    I hope this clarifies !

    Thanks

    Kind Regards,

    Anastas Yordanov