LMV242LD/AULF National Semiconductor, LMV242LD/AULF Datasheet - Page 13

• Manufacturer Part Number: LMV242LD/AULF
• Manufacturer: National Semiconductor

Specifications of LMV242LD/AULF

• Manufacturer's Type: Power Amplifier
• Number Of Channels: 1
• Supply Current: 12@5VmA
• Frequency (max): 2GHz
• Operating Supply Voltage (min): 2.6V
• Operating Supply Voltage (typ): 3/5V
• Operating Supply Voltage (max): 5.5V
• Package Type: LLP EP
• Mounting: Surface Mount
• Pin Count: 10
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Lead Free Status / Rohs Status: Compliant

Application Section
Extra attenuation Z between the coupler and the RF input of
the LMV242 can be achieved by 2 resistors R
according to Figure 3, where
or
e.g. R
To prevent reflection back to the coupler the impedance
seen by the coupler should be 50Ω (R
consists of R
with the formula:
e.g. with R
BASEBAND CONTROL OF THE LMV242
The LMV242 has 3 baseband-controlled inputs:
V
The actual V
applying a certain mask shape to the “Ramp in” pin, the
output voltage level of the LMV242 is adjusting the PA
control voltage to get a power level (P
PA, which is proportional to the single ramp voltage steps.
The recommended V
trol is 0.2V to 2.0V. The V
from 0V to V
input does not change the output level until the level reaches
• V
• TX_EN is a digital signal (performs the function
• Band Select (BS)
RAMP
“Shutdown/Transmit Enable”).
FIGURE 4. Simplified PA Control Loop with Extra
RAMP
Y
Signal
= 300Ω results in an attenuation of 16.9 dB.
signal (Base band DAC ramp signal)
Y
X
= 300Ω, R
RAMP
DD
in parallel with R
Z = 20 LOG (R
R
without malfunction or damage. The V
R
X
input value sets the RF output power. By
X
= [R
= 50 * [1 + (50 / R
RAMP
IN
Attenuation
O
= 50Ω → R
* (R
voltage range for RF power con-
RAMP
IN
Y
Y
+ R
/ [R
+ R
input will tolerate voltages
(Continued)
IN
IN
IN
)] / R
X
. R
+ R
OUT
= 58Ω.
Y
O
X
)]
). The impedance
Y
can be calculated
Y
/dBm) out of the
])
X
and R
20079530
RAMP
Y
13
about 206 mV, so offset voltages in the DAC or amplifier
supplying the R
output and increased power consumption.
Transmit Enable
Power consumption requirements are supported by the
TX_EN function, which puts the entire chip into a power
saving mode to enable maximum standby and talk time while
ensuring the output does not glitch excessively during
Power-up and Power-down. The device will be active in the
case TX_EN = High, or otherwise go to a low power con-
sumption shutdown mode. During shutdown the output is
pulled low to minimize the output voltage.
Band Select
The LMV242 is especially suitable for PA control loops with 2
PA’s. The 2 outputs to steer the V
controlled with the band select pin. When the band select is
LOW output2 is selected, while output1 is selected when
band select is HIGH. The not-selected output is pulled low.
Analog Output
The output is driven by a rail-to-rail amplifier capable of both
sourcing and sinking. Several curves are given in the “Typi-
cal performance characteristics”-section regarding the out-
put. The output voltage vs. sourcing/sinking current curves
show the typical voltage drop from the rail over temperature.
The sourcing/sinking current vs. output voltage characteris-
tics show the typical charging/discharging current, which the
output is capable of delivering at a certain voltage. The
output is free from glitches when enabled by TX_EN. When
TX_EN is low, the selected output voltage is fixed or near
GND.
FREQUENCY COMPENSATION
To compensate and prevent the closed loop arrangement
from oscillations and overshoots at the output of the RF
detector/error amplifier of the LMV242, the system can be
adjusted by means of external RC components connected
between Comp1 and Comp2. Exact values heavily depend
on PA characteristics. A good starting point is R = 0Ω and
C = 68 pF. The vast combination of PA’s and couplers
available preclude a generalized formula for choosing these
components. Additional frequency compensation of the
closed loop system can be achieved by adding a resistor
(and if needed an inductor) between the LMV242’s output
and the V
conductor for additional support.
TIMING DIAGRAM
In order to meet the timemask specifications for GSM, a
good timing between the control signals and the RF signal is
essential. According to the specifications the PA’s RF output
power needs to ramp within 28 µsec with minimum over-
shoot. To achieve this, the output of the PA controller should
ramp at the same time as the RF signal from the Base Band.
The ramp signal sets the controllers output to the required
value, where the loop needs a certain time to set this output.
Therefore the ramp should be set high some time before the
output has to be high. How much time depends on the setup
and the PA used. If the controllers shutdown functionality is
used, the shutdown should be set high about 6 µsec before
the ramp is set high.
APC
input of the PA. Please contact National Semi-
AMP
signal will not cause excess RF signal
APCS
of the PA’s can be
www.national.com