Knowledge Base

SX1276 transmission power managment.

I want to verify if my information about the Tx output power is correct or no, because i'm kinda confused, so if you could bear with me to tell you want i know or at least what i think it's true about this subject:
+ in Tx they are 3 power modes:

1- RFO: from -4 dBm to 15 dBm (Pout=Pmax-(15-OutputPower) = 10.8 + 0.6 * 7 - (15 - 15) = 15) 7 is the max value for the MaxPower and 15 is the max value for the outputPower so that's way the RFO can reach 15 dBm, but i don't know why they said it's only +14dBm? and set the PaSelect to 0 to use this mode and make sure the PA_Dac set to 0x04 (default value)

2- PA_Boost: from 2 dBm to 17 dBm (Pout=17-(15-OutputPower)) this is clear. set PaSelect bit to 1 to activate this mode. and make sure to set the PA_Dac to 0x04 (default value) (PA_DAC register = 0x84)

3- +20dBm: 20 dBm, to use this option we need to be in the PA_Boost mode (set PA_Boost bit to 1) and set the PA_DAC to 0x07 (PA_DAC register = 0x87).

About the RFO where i need to set 2 variable "MaxPower" and "Output Power", i don't know what is the right way to do that, i mean which one should i adjust to get the Tx power the user want to use. or should i set the "MaxPower" to 7 so the Pmax = 15 and from there i set the "Output Power" to get the Pout (which is the Tx power) the user wants, because it's gonna be easy to go from 15 to 0 by step of 1 dBm. hope one of you have a better solution?!

Now the last thing, the OCP, which is require for the PA_Boost and +20 dBm option because both works in high power (PA_HP) and i don't know how to set that register, i mean how to calculate Imax. i need help about this, and do i need to set this register for the RFO mode too?? if yes then how? (by the way, i know about the table of OCP in the datasheet and how to calculate the OCP from Imax, the problem that i don't know how to get or figure about the Imax.

One last question, is the order to configure the PaSelect Variable and MaxPower and Output Power and PA_DAC register and OCP register matters, my real confusion is about PaSelect variable and Output Power variable and PA_DAC register configuration order.

I hope i was clear and i will appreciate your help to correct me and confirm my information. Thank YOU.
Ok, to answer some of my questions:

what i said about RFO was right, but i still don’t know why they said it’s between -4 to 14 dBm and in the same datasheet in other section they said it’s 15 dBm. anyway, about how to set this in the register because you have 2 variable you need to set (maxPower, and outoutPower), you can notice we have 2 regions, from -4 to 0 dbm and from 0 to 15 dBm. for [-4, 0[ set the maxPower to 0 and that will give you a Pmax = 10.8 and from this equation Pout = Pmax - 15 + outputPower = 10.8 -15 + outputPower = -4.2 + outputPower, we can find outputPower = Pout + 4.2, and for the region [0, 15] we set the maxPower to 7 (the max value) so we will have this now , Pout = 15 - 15 + outputPower = outputPower.
About the PA_BOOST it a forward calculation nothing fancy, outputPower = Pout - 2 and don’t forget Pout should be between 2 and 17,
to switch betwen RFO and PA_BOOST, set the bit 7 in PaConfig register. and disable the +20 dBm option in the Pa_Dac register.
About the +20 dBm option, it's the same as PA_BOOST but instead of Pmax = 17, Pmax = 20 so outputPower = Pout - 5 , and you need to enable the PA_BOOST and then set the PA_Dac to 0x87, 7 to enable the +20 dBm option, , note : just by setting the outputPower to 0xf (15) you will get the 20dBm, and to disable this feature just set PaDac varaible to 4 ( set the PaDac register to 0x84) to disable it.

for the OCP, they have a table that gives you how to calculate the ocp value from the Imax,
ocp-trim [0-15], Imax [45, 120 mA] , Imax = 45 + 5 * ocpTrim
ocp-trim [16-27], Imax [130, 240 mA] , Imax = -30 + 10 * ocpTrim
ocp-trim > 27, Imax = 240mA , Imax = 240 mA

and about the Imax which is the current need for the Tx we can find this in the datasheet:
RFOP = 13 dBm uses 28mA
RFOP = 7 dBm uses 20 mA
PA_BOOST = 17 dBm uses 90 mA
+20 dBm opton uses 120mA

the OCP need to be enabled if you want to use the PA_BOOS.
about the order of the settings. i will just try to set the register in order, just in case.