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TPS3306 and noise

Dave Weinzierl
Expert 6380 points
Other Parts Discussed in Thread: TPS3306

I have a customer that is using TPS3306 and they belive noise is coupling into the WDI input.

This is a weakly driven pin that toggles and looks for transitions.  How is this pin sampled during transition?  Is there any way to calculate a noise margin for WDI?

 

  • 0
    TI__Expert 6380 points

    The way I read it, the thresholds are VIH (.7 VCC) and VIL (.3 VCC) with a 40K termination that will either be high or low. 

  • 0
    TI__Expert 5640 points

    The WDI pin is a logic input with Vih => 0.7*Vdd and Vil <= 0.3*Vdd.  The input must see an edge from a logic low to logic high in order to reset the watchdog timer.  You can think of this input an analogous to the clock pin of a D type flip flop or any other edge triggered signal.

    Internally, the WDI pin is driven by a pulse generator so that if the WDI pin is left open, then the watchdog input is automatically provided by the IC.  There is a 40kOhm resistor between the pulse generator and the WDI input pin so that you don't have signal conflicts when using an external WDI source.  The internal pulse generator stays low until a watchdog pulse is needed, then a high level pulse is generated for a few microseconds to reset the watchdog.