• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 64 subscribers
  • Views 90 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS3823: I want the /RESET line to go low (assert) and STAY low

Jeff Gray
Prodigy 80 points
Part Number: TPS3823

Tool/software:

In the circuit shown above, I am attempting to use the TPS3823 in an industrial application to turn off the gate of a FET when /RESET is asserted, i.e. when /RESET goes low.

For terminology, let's call the WDI signal CLK when it is pulsing high or low (1kHz in my application).  What I have found is that if WDI is kept high or low, the /RESET output is nominally de-asserted (high) and pulses low for a short time about once every 1.6 seconds.  This does seem to be the intended operation of the device, but not what I need.  I need the /RESET to stay LOW continuously when WDI is not getting a CLK signal.

Desired logic:

/MR            L    H    H         H

WDI           X    L     H      CLK

/RESET     L     L     L         H

I am going to try a modification of the circuit that is used to decouple the WDI signal (in the data sheet/3823A version) but I thought there might be an app note or circuit suggestion that I can use.

Thanks!

  • 0
    TI__Genius 14650 points

    Hi Jeff,

    Based on the information provided, you are looking for a latched output watchdog device. 

    For a latched output device you have limited options.

    1. If you want to use the TPS3823, you will need an external circuit to provide the latch. The simplest solution is going to be putting a resistor between MR and RESET which will create a voltage divider with the MR internal pull-up resistor when RESET goes low, which set the MR input below V(input low) causing the RESET to hold low until a HIGH signal is inputted to the MR pin, disabling the latch.
    2. Switch to a watchdog device with an integrated latch functionality. With an integrated latch, the latch is disabled when WDI gets CLK, no manual inputs needed.

    Please let me know which option works for you.

    Jesse  

  • 0 in reply to Jesse Villanueva
    Prodigy 80 points

    I would be interested in checking out a latched WDT, can you offer any part numbers? I am going through the "Supervisor & Reset" selection table but nothing obvious stands out.  I am not at all married to the TPS3823.

    Thanks for your help,

    Jeff

  • 0 in reply to Jeff Gray
    TI__Genius 14650 points

    Hi Jeff,

    I will follow up in email to further discuss our watchdog devices that has latched output.

    Jesse 

  • 0 in reply to Jesse Villanueva
    Prodigy 80 points

    Sounds good, thanks.