nRF52840 UART current high problem is discussed again

[Hannibalhz]

Dear Nordic Engineers

Our customer encountered a problem that is the UART of NRF52840 current value too high when the chip enters idle mode.

I found an old case and it gives a workaround that is resetting the power register of the UART.

Then I found Arduino gave another workaround, its way is to wait for UART transceiver to stop before disable the whole peripheral as implemented.

"I have figured this out, the walkaround (use backport to disable UART power) is not really needed, we only need to wait for uart transceiver to stopped before disable the whole peripheral as implemented by #684 . I guess eanble =0 is implemented to freeze everything including the task that turning off transceiver therefore leaving transceiver active and consume 900uA in idle."

I found this way as the same as our customer's method. They enabled PM_DEVICE and cleared NRF_UARTE_EVENT_TXSTOPPED at UARTE initialization and then UART current value will reduce from 400uA down to 160uA at system suspend.

So I wanted to get an update on this issue, because I didn't find a description of this issue in Errata of NRF52840 and I didn't find a workaround in SDK.

Best regards,

Hannibal

[Vidar Berg]

Hello,

It should be sufficient to run the UART suspend action (pm_device_action_run(<uart dev>, PM_DEVICE_ACTION_SUSPEND) to make the driver execute the power-down sequence here: https://github.com/nrfconnect/sdk-zephyr/blob/7ccc1a41bc4c27c73bb03f01ed6b05491ba5872d/drivers/serial/uart_nrfx_uarte.c#L1868.  The implemenetation follows the sequence documented in the product specification here: Low power

Have you tried measuring the current consumption when the UART instances are disabled by setting CONFIG_SERIAL to '=n' for comparison?

Best regards,

Vidar

EDIT: Is the application tested with out without a bootloader present? 

[PabloL]

Vidar Berg said:

EDIT: Is the application tested with out without a bootloader present? 

Hi, I have a higher current when I enable the bootloader in my board, let me ask: why did you ask that?

[Vidar Berg]

It could be that the bootloader is enabling the UART but not properly disabling it before branching to the main app. Do you see the same if you set CONFIG_SERIAL=n in your bootloader build?