Gilen Tell

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8 years, 8 months ago.

Current in TX with 14dBm

Hi,

I've noticed that the TX current measured in this example is about 110mA, but the configured power is 14 (14 dBm, the limit in Europe), and the datasheet of SX1272 says that current with this configuration should be about 30mA.

Is there any bug in the implementation of the libmdot "setTxPower" API function?

Best regards,

Gilen

Question relating to:

Last updated: 30 Sep 2015
Connecting to gateway, sending packets with a MultiTech mDot and entering deepsleep mode between transmissions. Lora, low power, mdot, multitech, Sleep

Hi again,

I have updated to the last version of libmdot ((1.0.7) and with the same configuration of transmission power of 14dBm, the current meassured in TX is about 55uA. With the previous version, as I comment when I opened this post, the current was 110uA.

Is there any changelog or any correction of bug about this issue? Had I reason when I said that it was excesive current with 14dBm?

Thank you and regards, Gilen

posted by Gilen Tell 31 Mar 2016

Hi again,

Finally I have detected the cause of those current consumption deviations. When the mDot does not have antenna connected the current in TX is 110mA. When the antenna is connected the current is 55mA. Until now I had never seen such behavior in a RF system. So any measurement must be done with RPSMA antenna.

This should have an explanation, but it is the task of mDot designers or Semtech SX1272 tranceiver manufacturer to explain it.

Cheers,

Gilen

posted by Gilen Tell 04 Apr 2016

1 Answer

Timothy Barr
8 years, 8 months ago.

Unfortunately since we are only using the PA_BOOST pin for RF output, current draw will typically be higher in general. The current draw spec for 14 dBm in the data sheet is for the RFO pin with the PA shut down.

So the utilization of PA_BOOST is the reason of higher current consumption. And what is the advantage of using the PA_BOOST instead of RFO_HF? If in Europe the regulations limit most bands to 14dBm, it would not be necessary to use the amplifier. It would be required only for 869.40- 869.65 MHz band with limitation of 500mW (27dBm) transmit power. Isn't it? Thanks, Gilen

posted by Gilen Tell 21 Mar 2016

The mDot is designed to operate both in the US and EU, so the high power output was chosen for the design. The latest LoRaWAN specification does support the higher power band in the EU as well so the higher power output is being used there also.

posted by Timothy Barr 21 Mar 2016