STM32WL55: High consumption by RF section

[Zedder]

Hello.

I'm using the Nucleo-WL55JC board with LoRaWAN End-Device firmware (US915 region).

To measure the current consumption of the RF section, I removed the JP2 (I_RF) jumper (as per the manual) and connected an ammeter.

The issue is that the RF section consumes around 80mA during reception, and the power consumption during transmission is also significantly higher than the datasheet values.

I checked the FE_CTRL_1 to FE_CTRL_3 signals, and they look correct. The SMPS output is about 1.5V, which seems fine.

However, as I understand it, the RF section's current consumption should not exceed 5mA during reception.

What can be wrong?

Measurements are attached.

[AScha.3]

Hi,

>and connected an ammeter.

How this is connected ? no ground loop ?

Did you check, your "ammeter" is showing real value, i.e. take an 1k resistor 3v3 to gnd, giving 3mA and check reading ?

[Zedder]

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How this is connected ? no ground loop ?

Did you check, your "ammeter" is showing real value, i.e. take an 1k resistor 3v3 to gnd, giving 3mA and check reading ?

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I'm using NRF-PPK2 for mesurement. Checked it with different resistors with current from 15µA to 150mA, everything seems correct - current corresponds to the resistance.

I tried different measurement methods: ammeter, ammeter with a USB isolator, ammeter as a power source connected to pins 16(3.3V) and 19(GND) with JP7(5V line) removed. The results were similar in all cases.

[Zedder]

One more thing.
After flashing my Nucleo with a simple "LED blink" firmware (with the radio disabled), I measured the current consumption of the radio module (JP2 / I_RF). It draws about 38 mA. Total consumption of the board is about 45mA.

I thought the problem might be uninitialized signals on the FE_CTRL_1...3 pins that control the radio switches. I tried initializing them with different output levels, but it didn't make any difference.

[AScha.3]

Hmmm...

again:

- you see 38mA , when radio OFF.

- but: in first post meas. you show some pulses ...xx mA, in between 0 mA . (right?) So here radio off = 0 mA .

- sure, its not damaged ? by static or Tx test without antenna ?

[Zedder]

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- you see 38mA , when radio OFF.

I see 38mA in a project generated by CubeMX without using the "SUBGHZ" module. This is a minimal "LED Blink" firmware.

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- but: in first post meas. you show some pulses ...xx mA, in between 0 mA . (right?) So here radio off = 0 mA .

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Right. This project uses the "SUBGHZ" module with the LoRaWAN stack (EndNode).

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- sure, its not damaged ? by static or Tx test without antenna ?

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I've never used the board without an antenna, but I can't be completely sure the chip is not damaged. That's what I'm trying to figure out. However, now I’m starting to doubt this behavior is normal for an undamaged chip.

[AScha.3]

Ok, but with "SUBGHZ" module active, power seems about zero, when not active rx or tx , so this seems normal.

But not the high current on rx only...

If board was new, not used by others, it should be ok. So check, on your rx setting, its not on rx/tx active mode (if there is such) or no pins "fighting" each other or something like this.

(I had on a cpu once similar too high current use, just a grounded pin tried to drive the pin hi - i found it and it was fine then.)

btw you have matching board for your frequency setting , 915M , hi or lo band version ?

And check in debug the setting of the control pins for RF / PA :

circuit from :

https://www.st.com/en/evaluation-tools/nucleo-wl55jc.html#cad-resources

...to be sure, power to RF/PA is really OFF, when you expect it and measure current.