nRF9160 Power Consumption high

[GJSea]

Hi,

I have the barest of PCBs with literally just the nRF9160, SIM slot and antenna, and have wired it directly to an Otii Arc, so there is no power circuitry either as it is supplied directly from the Otii. 

I've configured my project with all of the UARTs disabled, connected to AT&T LTE-M, have my PSM set to 360 minutes. After the connection has been established and the device enters PSM mode I'm observing the following

- Current consumption between the spikes is about 56uA which I'm fine with.

- If I include the PSM communication spikes the average consumption is around 1.4mA.

It seems the PSM request is being accepted:

Request

AT+CPSMS=1,,,"00000100","00100001"

Response

+CESQ: 99,99,255,255,24,47
+CEREG: 5,5,"2C34","0149FA16",7,,,"11100000","11100000"
+CPSMS: 1,,,"00000100","00100001"

Any ideas why the chip is drawing so much average power? I've attached my Otii traces highlighting the low power period, and the average current across multiple spikes.  

Thanks! Gavin

[Stian Røed Hafskjold]

Hi, can you please post the Otti project files. I have the software here, so I can have a look at it.

Regarding the ~50uA in idle, this probably caused by one of the UART peripherals staying in RX mode. Most likely because the logging module is active.

Based on the traces it seems like the spikes have an interval of 2.56 seconds which is indicating that the modem is in eDRX mode. Not PSM.

The CEREG notification also confirms this:

+CEREG: 5,5,"2C34","0149FA16",7,,,"11100000","11100000"

"11100000" means disabled. See the GPRS Timer 3 IE in 3GPP TS 24.008 Table 10.5.163a/3GPP TS 24.008.

The CPSMS read command only returns what is requested by the modem. Not what has been given by the network.

[GJSea]

Hi Stian,

Based on your observation that the device is in eDRX mode, I recall reading in another thread about the device not observing PSM if not registering on a HOME network. I was using Hologram which I believe always ROAMs, so I ordered an AT&T IoT OneRate SIM which magically connected to HOME and suddenly current consumption dropped to 17uA !!! 

So in summary, PSM will only be realized if the device registers to a HOME network using a cellular providers native SIM. ROAMing SIM's will only achieve eDRX power consumption profiles.

Thanks!!

[Stian Røed Hafskjold]

Hi Gavin,

Yes that is correct. Most networks will not allow PSM with roaming SIMs. Glad you figured out how to get it to PSM. It should ideally go as low as 2.7uA. But that is of course if nothing is running on the application core.