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TPS3606-33: WDI pin pulled high

Pavaman Panchamukhi
Prodigy 30 points
Part Number: TPS3606-33
Other Parts Discussed in Thread: TPS3600, TPS3610

Dear, 

I am using TPS3606 and i have observed that when the WDI pin is pulled high to 3.3V , at this point the WDI had voltage pulsating from 3.3V to 3.15 (ON-OFF-ON state) and  the /RST pin is generated pulses with 110mS on and 900mS off. Why is this erroneous behavior ? 

Can also suggest similar IC , where both VDD and VBAT can be used for powering the uC  and whenever VBAT goes less than xx threshold the device disable the output and no power is available to controller. 

  • 0
    TI__Genius 12630 points

    Hi Pavaman,

    Is VDD also 3.3V? Can you provide a schematic of your configuration?

    If WDI pin is floating or high impedance, the device will generate its own watchdog pulse, but the device will not reset in this case. The behavior you described sounds like the WDI pin is not meeting the high-to-low or low-to-high transition within the watchdog timeout (0.48 minimum and 1.12 maximum seconds) and the device is triggering a reset (between 60 and 140 ms). When you correctly pulse the WDI pin from high-to-low or low-to-high before 0.8 seconds (typical), does the device continue to reset?

    Does this behavior appear on multiple devices? Was your circuit working as expected at one point and then began to behave differently as you described?

    We have a few devices with Vbat (battery backup) and watchdog: TPS3618, TPS3600, TPS3606, TPS3610, TPS3617

    I will try to get this resolved as quickly as possible. The more information you can provide, the easier it will be to find the potential issue. Thanks

  • 0 in reply to Michael_DeSando
    Prodigy 30 points

    Hi

    Yes VDD is 3.3V. and VBAT is of 3.6V. The Mswitch pin is pulled low . 

    The WDI pin is pulled high to 3.3V with 10kohm, i observe transition on WDI pin from 3.3V to 3.15V .  Because of this transition the device triggers a reset.

    We observe at some instance in few devices the device is not providing Vout. Is WDI transition a cause for this .

  • 0 in reply to Pavaman Panchamukhi
    TI__Genius 12630 points

    Pavaman,

    On page 6 of the datasheet, in section "Saving current while using the watchdog", it states that if the WDI pin is externally driven high for the majority of the time-out period, a current of the pull-up voltage / 40 kohm can flow into WDI. I think this current flowing into WDI across the 10 kohm external pull-up resistor is causing the WDI pin to fluctuate voltage level. Because the WDI pin does not transition to logic low (0.3 x Vout), the device resets.

    Can you pulse WDI from a high to low or low to high transition to see if the device does not reset?

    Also, to improve the current consumption, it is recommended to keep WDI in low logic for majority of the watchdog timeout and then pulse from low to high and back down to low. Is it possible for you to use this configuration for your WDI signal?