I have a question what value should I set in the parameter “paDutyCycle” and “hpMax”
if the power set in “SetTxParams” is less than + 14dbm (the table in the datasheet is not complete or I misunderstood the principle of setting the radiation power)
and also want to know what practical application has the “RampTime” parameter in “SetTxParams”, thanks. 
Hi,
The architecture of the SX126x transmitter is a non-linear switching type. If you refer to Section 13.1.14 of the DS, you’ll note the output power is a function of TxParams(power) and PaParams(paDutyCycle, hpMax).
If maximum efficiency is required, set TxParams(power) to maximum (which sets the PA bias, VR_PA, to max) and trim the PaParams configuration to set the required output power. This will probably be an iterative process, and dependent upon PCB layout and BOM.
Alternatively, you can leave the PaParams as default and set the output power through configuration of TxParams(power) or a combination of both TxParams and PaParams. Again this will be an iterative process, dependent upon layout and matching network BOM.
Finally, TxParams(RampTime) determines the rise and fall time of the PA when the Tx is enabled. The impact of rise and fall time can be observed by monitoring the switching transient or dynamic adjacent channel power. RampTime can be configured to ensure compliance with any relevant regulatory requirements.
Semtech Support
thanks, I will experiment 