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Disable the Watchdog function of TPS65381 - while reprogramming

Jeevaaraam Sethuraman2
Prodigy 50 points
Other Parts Discussed in Thread: RM44L520, TPS65381A-Q1

Multi-rail power supply: TPS65381AQDAPRQ1

Micro-controller: RM44L520APZT

There is connection between TPS IC/pin-6 (NRES) and uC/Pin-31 (nPORRST) with pull-up. We face one issue regarding programing of uC using JTAG.

  1. First, we can able to program the uC (Unloaded, fresh uC), which enable the external watch dog (TPS IC – U1).
  2. In next time, if we try to program the uC, the JTAG not able to access uC.
    • Reason: 'NRES' is on LOW, which reset the uC (as it is connected to 'nPORRST').
    • Root cause suspected: When JTAG is trying to access uC, it will reset the uC and hence, uC will not able to serve the Watch dog to TPC IC. So, the TPS IC enable 'NRES' is to LOW state.

My query:

Kindly confirm whether there is any option to disable the Watchdog function only on selective cases (While programming, debugging) from uC 'RM44L520'. There is resistor between TPS NRES and uC nPORRST. At present, I have removed this resistor and pulled-up uC nPORRST to Vcc temporarily during development stage to avoid this RESET issue. However, this is not feasible, when I go for final release. I have to find a way to avoid this situation.

  • 0
    TI__Genius 12735 points

    Hello,

    Just to confirm, are you trying to disable the watchdog on TPS65381A-Q1? If yes, you can prevent a watchdog failure causing a reset by setting WD_RST_EN = 0 while in active state. This can be seen in Figure 5-16 "Device Controller State Diagram" in the TPS65381A-Q1 datasheet. We only recommend doing this to be able to debug software.

    Best regards,

    Layne J

  • 0 in reply to Layne J
    Prodigy 50 points
    Layne J said:
    We only recommend doing this to be able to debug software.

    Kindly suggest whether this provision can be used for actual run time (not only debug software). Because, when we try to disable the watchdog during run time, we are not able to disable it. Before, disabling the watchdog (Time interval = 10ms in our case), TPS resets the uC.

  • 0 in reply to Jeevaaraam Sethuraman2
    TI__Genius 12735 points

    Hello,

    I would like to highlight that the WD_RST_EN bit can only be written to while the device is in DIAGNOSTIC state. So the uC must set WD_RST_EN = 0 while in DIAGNOSTIC state. Once this is done TPS65381A-Q1 can be transitioned to ACTIVE state however the system loses the additional coverage of the uC that the watchdog provides so we recommend in a final system using the watchdog, although this is a choice you can make for your system.

    Best regards,

    Layne J