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TPL5000 as a Watchdog

Other Parts Discussed in Thread: TPL5000, TPL5100

Hi all,

I'm using the TPL5000 as a watchdog for my microcontroller. In the image my schematic. I have an unexpected  performance (at least for me...).

When the circuit is power on, the RESET_N pin of the TPL5000 runs ok, and my micro boots ok.

To test the circuit, the micro never sends a DONE signal, in order to test the wacthdog functionality. After 64 seconds of the power on sequence, the TPL5000 goes low the RESET_N pins, and my micro is reset. This is ok. BUT after the next 64s, the TPL5000 doesn't produce the RESET_N. Is after 128s when the TPL5000 produces a new reset. And the sequence is repeated every 128s. Step by step, that's mean:

1. Power on.

2. The TPL5000 produces a good sequence of the RESET_N pin. My app boots.

3. In my boot code I do a DONE pulse (10ms). To stablish my base time for the future watchdog reset (DONE pin)

4. After 64 seconds, the TPL5000 produce a reset and the micro is reset.

5. In my boot code I do a DONE pulse (10ms), again.

6. After 64 seconds, nothing happens.

7. After 64 seconds more, the TPL5000 produces a watchdog reset. That's mean, 128 seconds after.

8. Steps 5 to 7 are repeated...

Is this sequence rigth? I expected that the reset is produced every 64s, and not every 128s.

Thanks.

Joaquim.

  • Hi Joaquim,

    the sequence is correct, unfortunately you are not monitoring the WAKE signal.

    For simplicity I've quoted your sequence and I've added the WAKE signal

    1. Power on.

    2. The TPL5000 produces a good sequence of the RESET_N pin. My app boots.

    3. In my boot code I do a DONE pulse (10ms). To stablish my base time for the future watchdog reset (DONE pin)

    4. After 64 seconds, the TPL5000 produce a reset and the micro is reset. (this  RST is always send after power on, regardless the DONE)

    5. In my boot code I do a DONE pulse (10ms), again.

    6. After 64 seconds, nothing happens. ( the TPL5000 sends a WAKE because it has received a DONE)

    7. After 64 seconds more, the TPL5000 produces a watchdog reset. That's mean, 128 seconds after. (Since you have not send any DONE after the WAKE, the TPL5000 sends a RST)

    8. Steps 5 to 7 are repeated...

    So let me summarize the behavior of the TPL5000:

    After Power ON (PGOOD HIGH), the TPL5000 sends a Reset signal after (64s, your case) regardless the DONE signal.

    regards,

    Domenico

    If after the Reset the TPL5000 receives a DONE signal (within the next 64s) it will send a WAKE signal, if any DONE is received the TPL5000 will send a Reset signal.

    P.S. in your schematic you can remove the pull-up from PGOOD.

  • Hi Domenico,

    Thanks for your quick answer.

    I don't use the WAKE signal because my app is based in a very low power mode. I want to minimize the number of wake up in order to save power consumption.

    My original idea was to establish a timer in my app to send the DONE signal every 60 seconds.

    I undertand that the WAKE pin is useful to know if the TPL5000 is alive. So I have some questions:

    1. Is really necessary to read this signal?

    2. Must I read the WAKE signal and then to send the DONE signal?

    3. You mention that the TPL5000 sends a RESET signal regardless the DONE is sent. Do you mean that the TPL5000 will send always a RESET when I power on my hardware (first PGOOD low to high transition) ?. If yes, this is not good for me, because I will have a undesired reset 64s after my boot.

    4. Finally, following with the question 3 in order to understand the performance, if I power on my hard, I detect the first WAKE (after first 64 seconds) and I send a DONE, the TPL5000 will send a RESET?

    Thank you very much.

    Joaquim.

  • Hi Joaquim,

    the WAKE signal is not used to understand  if the TPL5000 is alive, it is used to wake up the microcontroller.

    The WAKE, RSTn and DONE implements the watchdog feature.

    1. If you do not need the WAKE there isn't  any need to send the DONE, it means that you want to reset the microcontroller every 64s.

    2. If you read the WAKE and then you send the DONE (such ase when your routine in the micro is finished) you implement a watchdog. In few word if your micro for any reason is locked in an infinite loop and it is not able to send the DONE, the TPL5000 will force a reset of the micro. If the micro is working fine (becasue it sends the DONE within 64s after each WAKE) then the TPL5000 wakes up the micro every 64s instead of reset it.

    3. after the Power On or after any low to high transition of the PGOOD, the TPL5000 sends a reset after the programmed time interval (in your case 64s)

    4. If you power on your hardware (with  PGOOD high) you detect a RESET after 64s, if the micro sends a DONE within 64s from the Reset the TPL5000 will send a WAKE, it will continue sending WAKE if it receives a DONE after each WAKE within 64s from the previous WAKE.

     

    In case you need just a timer which wakes up the micro every 64s without implementig the watchdog feature, you can simply short the TCAL and the  DONE together; and connect the WAKE and the RSTn to the micro. 

    The result will be the following:

    After power on (with PGOOD high) or after every low to HIGH transition of the PGOOD you detect a reset after 64s, then you will detect WAKE signals every 64s.

    regards,

    Domenico

     

     

  • Hi Domenico,

    Thanks for your answer.

    I think that the performance of TPL5000 is not appropiate for my app.

    I don't want a reset after 64s after the power on of my hard is done. This is because in the boot of my app I have to read several bytes of an eeprom, RTC, to configurate and RF transceiver, etc. and that means extra power consumption.

    There is any possibility to eliminate this function of PGOOD?

    Have you an other watchdog without this? maybe the TPL5100?

    Basically I need a watchdog with a min. timeout of 60 seconds, and very low power consumption <1-2uA.

    Thanks.

  • Hi Joaquim,

    the TPL51000 performs a power gating feature, so there isn't a watch dog.

    We are going to release in January a new timer with watchdog  which fits your needs.

    regards,

    Domenico