POWER_ON_N doesn't wake the module from ULPM until RESET_IN_N is triggered

Occasionally our WP7609s won’t wake from ULPM using the POWER_ON_N pin. We have to first trigger a module reset using RESET_IN_N, then triggering the POWER_ON_N pin will power the module on. It seems to be occurring about 20-30% of attempts to power on.

Has anyone experienced this behaviour? I can’t find any documents which discuss enabling/disabling the POWER_ON_N pin. Is there a configuration option anyone knows of which could be causing this?

Another possibility I’m considering is that the module’s MCU might be crashing…?

Keen to hear any ideas anyone else has :slight_smile:

Hi ben,

The AirPrime WP76XX module requires a low level signal (POWER_ON_N) that is used to switch the module ON. The signal is connected internally to the permanent 1.8V supply regulator inside the module via a pull-up resistor. Once VBAT_BB is supplied to the module, this 1.8V supply regulator will be enabled and so the POWER_ON_N signal is by default at high level.

The module can be powered ON when VBATT is applied then POWER_ON_N is asserted

Please refer to AirPrime - WP76xx - Product Technical Specification.pdf for more details

Please help to mark “Solution” if your question is answered. So the community could easily find the solution for their problems.

Hi Donald,

Thank you for your response. I appriciate the documentation you have provided.

We are supplying VBAT_BB continuously to the module via an attached battery, so pulling POWER_ON_N low should power on the module. Unfortunately though, occasionally this doesn’t occur. We first have to pull RESET_IN_N low, then pulling POWER_ON_N low will power on the module (as expected).

Please let me know if you have any more tips/tests for us to try :slight_smile:

Hi Ben,

Assertion time is the time required to keep POWER_ON_N at LOW level to ensure the module
can be powered ON successfully.
You can try with POWER_ON_N assertion time Minimum is 200 ms.

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