Reset when switching on modem

[Artnia]

Hello,

we’re currently facing an issue regarding the start-up of the nrf9151 modem.

Its a custom PCB and closely follows the schematic of the nrf9151 DK.
For first test SW we’re using the AT-Commander example and added our own overlay.

For testing we’re sending AT+CFUN=1 to enable the Modem. After approximately 1 Second the Module is performing an reset.
We observed huge current draw on the Vdd_Gpio line. We’re using a linear regulator for the Vdd_Gpio voltage which is maxed out at 300mA.
As more current is drawn the voltage collapses and therefore the module is performing an reset.

To take the voltage regulator out of the equation I bridged the regulator and supplied it together with Vdd out of the PowerProfiler directly with 3,3V.
Only to see the exact same result and the current maxing at around 1.2A. 

The problem does not occur, when no SIM is inserted. Probably the modem does not switch on then? 
Without the SIM inserted the following command leads to the same issue: AT%XVBAT

Tested on 2 different PCBs.

Do you have any idea, where this behavior could lead from?

[Hakon]

Also, can you read out RESETREAS register to check what it says?

[Artnia]

Hi Hakon,

is there a command for reading RESETREAS via AT?

Attached is the schematic, would be nice if you made the ticket private.

Thanks!

PublicSchematic.pdf

[Hakon]

Artnia said:

is there a command for reading RESETREAS via AT?

I don't think so, but you read it from software.

[Artnia]

Hi,

in my own software reset reason is

[00:00:00.302,276] <inf> Reset reason: 0x00000000

// Get reset reason. 1=RESETPIN, 2=DOG, 196611=CTRLAP ...

// docs.nordicsemi.com/.../power.html

uint32_t reset_reason = nrf_power_resetreas_get(NRF_POWER);

nrf_power_resetreas_clear(NRF_POWER, reset_reason);

LOG_INF("Reset reason: 0x%08X", reset_reason);

I get reset also with at_monitor sample which switches modem on via code, instead of AT commands.

Also without any custom overlay but just by using the 9151dk as target board I get the same behavior.



Did you have a chance to check the schematic?

[Hakon]

DEC0 should not be supplied by 3.3V. This is likely the reason for why you are seeing the strange behavior. Please cut the 3.3V line that goes to the DEC0 pin but leave the capacitor still connected. See if this fixes the issue for you. 

[Artnia]

Hi Hakon,

thanks a lot. That was it