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How To Apply UJA1075ATW Watchdog?

Question asked by Bright Wang on Oct 21, 2018
Latest reply on Oct 30, 2018 by Tomas Vaverka

HELLO

According To Datasheet And Following Diagram Of UJA1075ATW Here Is Not WDI (Watchdog Input) To Be Periodically Kicked. So We're Confused About The Mechanism Of Watchdog Timer. In Our Case We Want To Apply Watchdog For A System Supervisor To Monitor MCU's Status. IF MCU Behave Abnormal Then Reset MCU For 3 Times. After 3-Times Reset Pull EN Pin As High To Turn Off External Gate / Switch For A Prevention That A Power Source Cause Malfunction To Relay / Motors Upon Seat / Sunroof / Mirror.

Here Are The Questions:

1. What Different From 

UJA1075ATW/5V0/WDJUJA1075ATW/5V0WD,1

 

2. In Datasheet We Don't See Much About Watchdog Timer'ss Mechanism.

We Want To Make Sure Does The Watchdog Support

 

2-1 Kicking Dog Method - We Designed Our First Engineering Board With Maxim MAX16998AAUA/V+ And Due To Cost Issue We Find NXP SBC Will Be Great Choice In Replacement Of Old Design With 1 LDO / 1 CAN / 1 LIN / 1 Watchdog. Original Design:

MCU Periodically Kick Dog To Prevent Bite-On

Once Timeout The Mentioned Watchdog Will Reset MCU For 3 Times

If MCU Stay In Malfunction Without Kicking Dog Then Set SBC Enable Pin Active High To Turn Off System Power Source For Relay To Motor.

2-1-1. Can We Depend SPI Clock To Judge External MCU's Status Then Decide Timing To Reset The External MCU?

2-1-2. Can We Reset The External MCU When The MCU Is Broken? By RSTN Level?

2-1-3. What If A Situation Like MCU Is Broken And Drop-Down The Level Of WDOFF Will Be?

2-2 We Don't See Any Details About The Built-in Watchdog. First General Watchdog Required To Be Kick But The UJA1075 Seems No WDI (Input Pin). Our Problem Is The Watchdog Can Be Configured By SPI To Register For 3-Time Reset Mechanism? (Enable RSTN Pin To Reset External MCU For 3 Times)

2-3 

Looks Like Dog Kicks Are By SPI TO NWP. Problem Is Here Is Not Register Address Definitions In Datasheet.

 

3. Any Application Note Has Enough Information For Such A SBC Like UJA1075ATW?

 

4. Here Is 2 Sets Of Wakeup Pins. What Do Them Purpose On? Any Differences?

 

5. What Is The LIMP Pin For? I See A Description In Datasheet Tells LIMP Is For Overtemp Protection Use? 

 

6. Here Is 2 Wakeup Pins Input To SBC. I Wonder What Situation Will Apply 2 Wakeup Pins?

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