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TMS320F28335: When the reset pin of TPS3307-18 is connected to the XRS pin of TMS320F28335, what kind of abnormalities will occur?

user4637774
Intellectual 660 points

Part Number: TMS320F28335
Other Parts Discussed in Thread: TPS3307-18-Q1,

The reset pin of TPS3307-18-Q1 is of push-pull type. When it is connected to the XRS pin of TMS320F28335 (which is supposed to be of open-drain type), what kind of abnormalities will occur?

  • +1
    TI__Genius 17460 points

    Hello,

    We only recommend open-drain devices to drive our XRS pin. This is because our reset pin is both an input and an output. This will cause contention when the device attempts to assert reset.

    Best,
    Matt

  • 0 in reply to Matt Kukucka
    Intellectual 660 points

    What kind of abnormalities might occur if the TPS3307-18 is used to drive the TMS320F28XX? Is the abnormality likely to occur during power-on startup or during operation, or both? Thanks.

  • 0 in reply to user4637774
    TI__Genius 17460 points

    The bus contention condition can occur when the internal watchdog triggers a reset. During this event, both the TPS3307-18 (trying to drive high) and the internal watchdog circuit (driving low) would simultaneously attempt to control the XRS pin, potentially causing:

    • Excessive current flow between the devices (effectively shorting the FETs)
    • Damage to output drivers
    • Unpredictable reset behavior (system malfunction)

    This abnormality would occur during operation when the watchdog reset is triggered. The datasheet explicitly states that if the XRS pin is driven by an external device, it should be done using an open-drain device.

    Best,
    Matt

  • 0 in reply to Matt Kukucka
    Intellectual 660 points

    Will the C2000 fail to start when the push-pull output reset is used for the C2000, and does it occur when the device is powered on?

  • 0 in reply to user4637774
    TI__Genius 17460 points

    Hello,

    F2833x should start if the reset timing is respected for power sequencing. The contention issue occurs if the WD asserts a reset on XRS. If you use a push-pull reset circuit on XRS, the WD won't be able to properly assert a reset and could leave the device in an undefined state.

    Best,
    Matt