LR1110
User Manual
Rev.1.0
UM.LR1110.W.APP
March 2020
73 of 130
Semtech
9.1.1 Low Power PA
For maximum efficiency, the low power PA should be operated with a maximum VR_PA near 1.35V. To get VR_PA = 1.35 V
the user should set
TxPower
= 14. At this setting, the PA can deliver up to 15 dBm output power, constant over the specified
battery supply range. The actual maximum output power can be set according to the duty cycle setting (
PaDutyCycle)
. If
needed, the output power can be decremented in steps of 1 dB from maximum by using
TxPower
< 14.
The VR_PA variation over the programmed power
TxPower
for
different supply voltages and
PaDutyCycle
condition
s
is
depicted in
Figure 9-3: Low Power PA VR_PA Voltage vs. TxPower
here below (valid for VBAT and VREG supplies, in both LDO
or DCDC configurations).
Note: All figures in this chapter are indicative and typical, and are not a specification. These figures only highlight the
behavior of the PA over the various parameters and conditions.
Figure 9-3: Low Power PA VR_PA Voltage vs.
TxPower
9.1.2 High Power PA
For maximum efficiency, the high power PA should be operated with a maximum VR_PA near 3.1 V. To get VR_PA = 3.1 V
the user should set
TxPower
=22. At this setting, the PA can deliver up to 22 dBm output power. The output power in this
case will inevitably vary when the battery voltage drops below 3.3 V. The actual maximum output power can be set
according to the
PaDutyCycle
and
PaHpSel
. If needed, the output power can be decremented in steps of 1 dB from
maximum by using
TxPower
< 22.
The VR_PA variation over the programmed power
TxPower
for
different supply voltages and duty cycle (
PaDutyCycle
)
condition
s
is depicted in
Figure 9-4: High Power PA VR_PA Voltage vs. TxPower
here below.
The internal regulator for VR_PA has 200 mV of drop-out, which means VBAT must be 200 mV higher than the VR_PA
voltage in order to attain the corresponding output power.
For example:
