TPS3813K33 reseting immediately after power up.

Hi Robert,

As stated in the datasheet, after the 25ms delay and release, the lower boundary of the first WDI window is disabled until after the frist WDI pulse is detected. Is it possible to attach a waveform showing VDD RESET and WDI signals, and a schematic of your application using the TPS3813? This will help us better support your issue. Thanks!

Regards,

Darwin

Hi Darwin,

Thanks for your help. CH2 (green), 3.3V supply CH1 (yellow) reset pin and CH3 (Purple) WDI pin.

My understanding is that after power on reset the watchdog should not start operating until the first rising edge of WDI. Is that correct? Otherwise when we try and program the uC it will continually taken into reset by the watchdog.

Many thanks

Robert.

Hi Robert,

This waveform looks like the WD is operating correctly. For startup, after the 25ms delay, RESET goes HIGH. Even though the lower boundary is disabled, the window (set to 250ms) is created. If there is no WDI pulse at this time, RESET will go LOW and try to reinitialize the uP again.

How much time does it take to program the uP? Perhaps a longer window will delay enough to program the IC?

Regards,

Darwin

Hi Darwin,

We will have to add some additional logic circuitry which can hold the reset high until  programming is completed.

Thanks for you help to clarify this Darwin.

Cheers

Rob

Sorry Darwin one final question.

Do all TI watchdogs work in this way or do some only initialise on the WDI input going high.

Cheers

Rob

Hi Robert,

Our WD timers are usually rising edge trigger or edge detect triggers.

Have you seen the TPS3823? WD can be disabled by open circuiting the WDI pin. This way, you can disable the WD, program the IC, then send the WDI pulses using the app note below:

http://www.ti.com/lit/an/slva145/slva145.pdf

Regards,

Darwin 

Hi Darwin

Is there any in the EP range with this feature??

Cheers

Rob

Hi Rob,

Unfortunately, we don't currently have a EP version of the disable feature. Since the TPS3813 is the only option, you may have to turn on the rail to the uP, initialize, then bring power to the TPS3813.

Please let me know if this helps!

Regards,

Darwin

Hello Darwin,

According to http://www.ti.com.cn/cn/lit/ds/symlink/tps3813k33.pdf

"After the reset of the supervisor is released, the lower boundary of the first WDI window is disabled. However, after the first WDI pulse low-to-high transition is detected, the lower boundary function of the window is enabled. All further WDI pulses will need to fit into the configured window frame."

On the waveforms, there is NO "first WDI pulse low-to-hi transition" and if the above document is correct, the WD is not active. Why do we see the RESET pulse being asserted?

Regards,

Piotr

Hi Piotr,

The watchdog is still active, only the lower  boundary of the first WDI window is disabled.  The window is still set to 250ms and if no WDI pulse occurs in this time, RESET will go low.

Very Respectfully,

Ryan

Hello Ryan,

The documentation is very clear to explain what is required "after the first WDI pulse'.

1. Reading this document my impression was that the activation of the WD feature is under the software control - the first WDI pulse will do it. So, software my take whatever long time (or not at all) to issue the first WDI.

Is there something in the documentation specifying that the use of the WDI is not optional?

2. Is there a similar part which would have the WD feature activated by the first WDI pulse/transition?

Regards,

Piotr

Hi Piotr,

This application note describes how similar devices can have their WD feature disabled and then re-enabled.

http://www.ti.com/lit/an/slva145/slva145.pdf

Very Respectfully,

Ryan