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TPS3850-Q1: Watchdog behavior when SET0 and SET1 are in high impedance state

Arie Li
Expert 3390 points
Part Number: TPS3850-Q1
Other Parts Discussed in Thread: TPS3850

Hi Experts,

What's the behavior of TPS3850 when SET0 and SET1 are in high impedance state? Is the watchdog disabled or enabled?

The user's case is as below, two modes are used, SET0 and SET1 pins are connected to MCU. During MCU initialization period, the SET0 and SET1 status is high impedance and there is no WDI signal, how will the watchdog behave in such situation? Will WDO keep reseting the MCU? Thanks.

Arie

  • 0
    TI__Genius 12630 points

    Arie,

    In high impedance state, the SET0 and SET1 are undefined and my guess is most likely logic low.For the case you describe, a pull-up or pull-down resistor is recommended to set a definite state when the MCU is in high impedance. Maybe the default state is SET0 pulled-up to a voltage and SET0 pulled-down to GND to set the initial state as disabled. Then when the MCU turns on, it can send the proper voltage level to the SET pins to initialize the watchdog timeout.

  • 0 in reply to Michael_DeSando
    TI__Expert 3390 points

    Hi Michael,

    Thanks for your reply. Could you please help to confirm the logic status when SET0/1 are in high impedance state? If SET0/1 are in logic low, it means the WDO will reset the MCU during MCU initialization, right?

    If pull-up and pull-down resistors at SET0/1 pins are needed, what value do you suggest? Should 10k be ok here? Thanks.

    Arie

  • 0 in reply to Arie Li
    TI__Genius 12630 points

    Arie,

    The SET0/1 are undefined in high impedance state. It really depends what charge if any is still on the pin and what the pin is connected to. My guess of being low is on the assumption there is no driving signal and there was not a driving signal previously and nothing is connected to the pin. The logic value on the SET0/1 pin can also maintain the previous logic value before the input went into high impedance so that is why it is undefined. I can't confirm the logic when in undefined voltage state. A 10kohm pull-up or pull-down resistor will work to put the pin in a definite state when the input is high impedance.