STM32WE5 SubGHz_Phy Middleware Questions

[JesusAVC]

Hello everyone

We are developing a prototype of vibration monitor system . Now we are in optimization stage , reducing the power of the device . We are using SeedStudio Lora E5 HF (STM32WE5) (US915) https://files.seeedstudio.com/products/317990687/res/LoRa-E5+module+datasheet_V1.0.pdf  , and programing it using STM32CubeIDE and this code base https://github.com/Seeed-Studio/LoRaWan-E5-Node/tree/qian. 

Our target is to reduce the tx power . However there's many configuration around that and it's not clear the final dBm . This module can give up to 22dBm on TX according to the specs . We would like to reduce it to 6dBm to save power .

Right now I'm playing around with SUBGRF_SetTxParams function and I was able to see a change in current consumption when the device is transmitting .

But still having some these questions :

1. How can I calculate or know what is the final dBm ? to achieve the 6dBm
2. Using this official middleware guaranteed the FCC certification or should we pass the certification process again ? 

Thanks in advance

[ahsrabrifat]

Modify the function call to use Low Power PA (RFO_LP) and to Set TX power to 6 dBm

The corrected Function Call has to be like this.

SUBGRF_SetTxParams(RFO_LP, 6, RADIO_RAMP_40_US);

[JesusAVC]

Thanks for the reply

I would like to  understand.According to the function documentation

the range is -18dbm to 13dbm . However my radio specs say it can support 22dbm TX (US915)

Is this a Gain/attenuation to be applied to the total 22dbm ? .

Is RFO_LP 14dbm  and RFO_HP 22dbm ?

How can I have a estimated practical value ? I mean 6dbm should give me TX current of 20mA  @3.3V ?. By default I get around 110mA

I want to limit the final TX  power to 6dbm.

[STTwo-32 · Accepted solution]

Hello @JesusAVC 

First, for the FCC certification process, you should contact the sales and marketing team of your component (the SeedStudio Lora E5 HF) about the steps to follow.

For the settings of the Transmission power, as suggested by @ahsrabrifat you should use the "SUBGRF_SetTxParams" function that will set the final TX power to 6dbm. 

For the question "Is RFO_LP 14dbm and RFO_HP 22dbm?" as you can see on the Table 32 of the DS13105 Rev 12, Max RF output power is +15 dBm for low-power PA (only with optimal parameters). And +22 for high-power PA. 

Finally, about the consumption, it depends on your system, what peripherals are used, ... So, the best way is to test it on your own code and HW. Also, the Optimal settings will help to minimize the consumption. Helpful details are available on the AN5457. 

Best Regards.

STTwo-32