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TPS3813: Does it really matter how exactly to trigger WDI if there are some impulses within WINDOW FRAME exists? - WDT for UART communication

Part Number: TPS3813

We want to use TPS3813 for UART communication monitoring. We cannot form our own triggering impulses as impulses belong to an application - i.e. UART communication, which MASTER-SLAVE perform between each other.

The method of monitoring is well known and is as following:

If MASTER doesn't see responses from SLAVE it wants to perform reset of the SLAVE. In order to do that, RX of the SLAVE will be connected to WDI and once MASTER doesn't receive responses from SLAVE's TX it will stop transmitting from it's own TX (this stop is a part of coding in the app), which will cause WDI seeing impulses of UART communication. This will cause timeout on WDT and SLAVE will be reset.


The problem is that regular WDTs are available for maximum 1.6s typ (were 1.12s is min). In our case MASTER is quiet for a bit more than 1.12s (but less 2s), so we need higher than 1.12s timeout. With TPS3813 we seems can configure for that. However it's quite complicated to understand boundaries, especially lower window frame, and how exactly it works as this is not as other "normal" Watchdogs.

We configured WDT=WDR=Vdd (window typ 2.5s)

Boundary violations, lower window frame and other things from datasheet absolutely mind blowing. So basically, is that enough just to trigger WDI anyhow without much care about boundaries? 

What we can guarantee is the following: some impulses will always exist during WINDOW FRAME. The question is as simple as this: "If there are multiple impulses exist within WINDOW FRAME would they keep RESET high all the time regardless of either rise or fall edge was the first in the beginning of the window"? 

  • Hi SRD,

    I will have a product expert on this part take a look into this further.

    Thanks,

    Abhinav.

  • Hello SRD,

    Please note TPS3813 detects rising edges on WDI so if multiple impulses exist within the Window Frame, the first rising edge would prevent a reset, but the next rising edge must be within the next window frame, otherwise a reset will occur. It doesn't matter what provides the impulses so long as the impulse meets the VIL and VIH requirements to be detected and meet the timing requirements based on the watchdog configuration.

    I believe the master/slave configuration will work, but do you want the window watchdog with early impulses causing a reset? Or would it be better to use a standard watchdog meaning only late/missing impulses cause a reset? We have standard watchdogs available if this will work better for the application.

    Please let me know how I can support further.