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TPS3851: Watchdog recommendation

Aivaras Sakauskas
Intellectual 1600 points
Part Number: TPS3851
Other Parts Discussed in Thread: TPS3820-Q1, TPS3820

Hi,

I am looking for a watchdog timer which would give an output (high or low) when input pulses meet timing requirements. When Input is low, output should go and stay in a high or low state.

The TPS3851 goes low but then goes to a high impedance state. Can you give me a device recommendation or a solution for this?

The idea of this is to combine the WDO output with an MCU output with an AND gate and have a 'safe' output.

Thank you.

  • 0
    TI__Genius 9375 points

    Hi Aivaras,

    Have you taken a look at one our watchdog supervisors such as the TPS3820-Q1 which has one output for both /RESET and WDO? This may be the solution you are looking for.

    Thanks,
    Abhinav.

  • 0 in reply to Abhinav.Sharma
    Prodigy 40 points

    Hi Abhinav,

    Aivaras asked this question on my behalf. Unfortunately, the TPS3820 doesn't look suitable; I am looking for a device that asserts the output when WDI stops toggling, and doesn't de-assert the output until WDI starts toggling again. The TPS3820 appears to assert RESET for only 25 milliseconds or so (td in datasheet figure 1).

    This is of course a common design for watchdog timers - if connected to a microcontroller's reset pin, how would the toggling ever restart unless the reset was de-asserted - but isn't what I'm looking for as I'm gating a safety output rather than resetting a microcontroller.

    Thanks.

  • 0 in reply to Michael Tandy
    TI__Genius 9375 points

    Hi Michael,

    You can actually achieve this functionality by default with this device. Please take a look at the industrial version of the datasheet: http://www.ti.com/lit/ds/symlink/tps3825.pdf. Section 8.3.4 explains how the output will actually latch, which I believe is your intent.

    Thanks,
    Abhinav.