LLCC68 PA output power level problem

  • 22 January 2024
  • 3 reacties
  • 32 keer bekeken


Here is my configuration for the "LLCC68MB2BAS_868MHz" evaluation board from SEMTECH

Test equipment :

R&S FSU spectrum analyzer in SPAN = 0 mode

Oscilloscope: FLUKE 200Mhz

Battery supply 4.1V


System requirements: Output power = +14dBm


To obtain +14dBm RF output, the configuration found is :

Padc (paDutyCycle)= 3

Pahpm (hpMax)=3

Txdbm (SetTxParams)= 22


regModParam default =1 (DC-DC + LDO)


Observation of the power envelope of frames transmitted after board power-up.


Frames                         Pout start         Pout end          Deviation

View burst n° 1            7.5 dBm              11.7 dBm            4.2 dB

View burst n° 2            11.5 dBm            13.3 dBm            1.8 dB

View burst n° 3            12.6 dBm            13.96 dBm         1.36 dB

View burst n° 4            13.3 dBm            14.26 dBm         0.96 dB

View burst n° 5            13.9 dBm           14.36 dBm         0.46 dB



Battery voltage is stable and constant 3.95Volts.

Voltage Vdd = 3.3 volts (stable)

Voltage VrPA = 3.14 volts (stable)

Voltage Vref = 1.5 volts (stable)


Translated with (free version)


Burst n°1 :


Burst n°2


Burst n°3 :


Burst n°4 :

Burst n°5 :


VrPA voltage at 1st view :


Conclusion :

SEMTECH's "LLCC68MB2BAS_868MHz" board shows unsatisfactory behavior in terms of RF transmit power level.

This observation is observed whatever the configuration of the PA parameters (paDutyCycle, hpMax, SetTxParams), but with abnormal behavior, for example:


Padc (paDutyCycle)= 2

Pahpm (hpMax)=2

Txdbm (SetTxParams)= 22


The average power will be around +9dBm with a 3 dB variation within the frame, then with each new frame, the power drops by around 1 dB. After 10 frames, power is stable at +3 dBm and not at +14 dBm as indicated in the datasheet:

DS_LLCC68_V1.0-1.pdf table 13.21 page 71/106.

If an SEMTECH expert could respond to this problem and indicate how to eliminate this strange behavior.


The LDO or DC-DC+LDO parameter has no effect on this finding.

3 reacties

Reputatie 7
Badge +6

Hey @fpatrice2008,

Welcome to the IoT Community!
Thanks for creating this topic. Are you testing this on our network?

I looked in the Things Portal to see if I could find an account with the data from your forum profile, but without success. Do you have an account for the Things Portal? If so, what information is this account registered to?

We would like to help you further, but we are not Semtech experts. We therefore do not have all the substantive knowledge about the Semtech equipment.


Thank you for your reply,
No, I don't have an account on "Things portal".
The "Lora-developper.semtech" site no longer works and it is difficult to get answers on the technical aspects of LoRa components. I thought I would be able to find answers or technical exchanges here.
The Semtech product is integrated into a simple environment whose objective is to achieve private point-to-point communication, not network communication.  
As a radiofrequency specialist, I don't understand the strange behavior of the LLCC68 circuit when transmitting.

Translated with (free version)

Reputatie 7
Badge +6

Ah okay, I get it. Unfortunately, we do not have the knowledge to help you with this. Our apologies!