High current consumption (~670 µA) in eDRX and PSM on nRF9151 DK

[Hassan0]

Hello,

I am currently working on power consumption optimization using the nRF9151 DK (PCA10201).

Setup:
- Board: nRF9151 DK
- Measurement tool: Power Profiler Kit 2 (PPK2)
- Power connection:
- PPK2 VOUT connected to VDD-nRF
- PPK2 GND connected to board GND (P21)
- The jumper between VDD-5V and VDD-nRF is removed to isolate the nRF9151

Issue:
The modem appears to enter low power modes (eDRX and PSM), but the measured current remains around 670 µA, which is much higher than expected.

Measured vs expected:
- Measured current: ~670 µA
- Expected current: a few µA (based on Nordic documentation)

Configuration:
- eDRX configured with a cycle of ~22 minutes
- Multiple eDRX configurations have been tested (different values), but the current consumption remains the same
- Similar behavior observed when testing PSM (no significant reduction in current)

Observations:
- This current level (~600–700 µA) could correspond to an active peripheral (e.g. UART)
- It is unclear whether powering VDD-nRF fully isolates the nRF9151 or if other components on the DK are still contributing

Additional info:
- The modem is attached to the network
- We tested a similar setup on another module and were able to reach µA-level consumption, so the issue seems specific to this setup

Questions:
1. Does powering VDD-nRF fully isolate the nRF9151 on the DK?
2. Could an active UART or another peripheral explain this ~670 µA consumption?
3. Are there specific steps to ensure the system reaches true ultra-low power (µA range) in eDRX/PSM on the nRF9151 DK?

Any help would be greatly appreciated.

Thank you!

[Håkon Alseth]

Hi,

 

Your setup for measuring current is correct.

2. Could an active UART or another peripheral explain this ~670 µA consumption?

Yes, this is usually the reason why you are seeing a higher floor current than 3 uA.

 

3. Are there specific steps to ensure the system reaches true ultra-low power (µA range) in eDRX/PSM on the nRF9151 DK?

Have you disabled UART for instance? Check if "CONFIG_SERIAL=n" is set on your side.

  

Kind regards,

Håkon

[Hassan0]

Hi Håkon,

Thank you very much for your clear answer.

I have a couple of follow-up questions to better understand the recommended approach:

1. If I disable UART using CONFIG_SERIAL=n, I assume I will no longer have access to AT commands via UART. In that case, does it mean I need to rely only on a C firmware implementation (using the nRF Connect SDK / LTE link controller APIs) to configure PSM/eDRX and operate the modem?
2. Is there any recommended or supported way to disable UART at the hardware level on the nRF9151 DK (for example using solder bridges or board configuration), in order to reduce power consumption while still keeping some form of debugging or alternative interface if needed?

Thank you again for your support.

Kind regards,
Hassan

[Håkon Alseth]

Hi Hassan,

 

I would recommend that you look into using serial lte modem if you require AT commands:

https://github.com/nrfconnect/ncs-serial-modem

 

You can set it up in sleep mode: https://docs.nordicsemi.com/bundle/addon-serial_modem-latest/page/app/at_generic.html#power_saving_xsleep 

Hassan0 said:

If I disable UART using CONFIG_SERIAL=n, I assume I will no longer have access to AT commands via UART. In that case, does it mean I need to rely only on a C firmware implementation (using the nRF Connect SDK / LTE link controller APIs) to configure PSM/eDRX and operate the modem?

Yes, this is correct. PSM is automatically requested. You can look at samples like ncs/nrf/samples/net/udp for a smaller example that provides minimal communication.

 

Hassan0 said:

Is there any recommended or supported way to disable UART at the hardware level on the nRF9151 DK (for example using solder bridges or board configuration), in order to reduce power consumption while still keeping some form of debugging or alternative interface if needed?

The issue is keeping the uart active inside the nRF, which causes the peripheral clock tree to be on while in sleep/idle mode, not the external physical connection itself.

 

Kind regards,

Håkon