Detailed Description
The MAX2242 is a linear PA intended for 2.4GHz ISM-
band wireless LAN applications. The PA is fully charac-
terized in the 2.4GHz to 2.5GHz ISM band. The PA
consists of two driver stages and an output stage. The
MAX2242 also features an integrated power detector
and power shutdown control mode.
Dynamic Power Control
The MAX2242 is designed to provide optimum power-
added efficiency (PAE) in both high and low power
applications. For a +3.3V supply at high output power
level, the output power is typically +22.5dBm with an
idle current of 280mA. At low output-power levels, the
DC current can be reduced by an external DAC to
increase PAE while still maintaining sufficient ACPR
performance. This is achieved by using external resis-
tors connected to the BIAS pin to set the bias currents
of the driver and output stages. The resistors are typi-
cally 8kΩ. Typically, a DAC voltage of 1.0V will give a
280mA bias current. Increasing the DAC voltage will
decrease the idle current. Similarly, decreasing the
DAC voltage will increase the idle current.
The BIAS pin is maintained at a constant voltage of
1.0V, allowing the user to set the desired idle current
using only two off-chip 1% resistors: a shunt resistor,
R2, from BIAS to ground; and a series resistor, R1, to
the DAC voltage, as shown in the Typical Application
Circuit. Resistor values R1 and R2 are determined as
follows:
V
MAX
= 1.0 + (1.0
✕
R1) / R2;
(I
CC
= 0, V
DAC
= V
MAX
) (1)
I
MAX
= (1.0
✕
1867)
✕
(R1 + R2) / (R1
✕
R2);
(I
CC
= I
MAX
= max value, V
DAC
= 0) (2)
I
DAC
= (V
DAC
- 1.0) / R1 (3)
I
MID
= (1.0
✕
1867) / R2;
(V
DAC
= 1.0V or floating) (4)
I
CC
= 1867
✕
I
BIAS
(5)
where
V
MAX
= is the maximum DAC voltage
I
MAX
= is the maximum idle current
I
MID
= is the idle current with V
DAC
= 1.0V or not
connected
V
DAC
= is the DAC voltage
I
DAC
= is the DAC current
If no DAC is used and a constant idle current is
desired, use equation 4 to determine the resistor values
for a given total bias current. Only R2 is required.
MAX2242
2.4GHz to 2.5GHz
Linear Power Amplifier
6 _______________________________________________________________________________________
Pin Description
Power Detector Output. This output is a DC voltage indicating the PA output power. Connect a
Bias Control. Connect one 8kΩ resistor from BIAS to GND and one 8kΩ resistor from BIAS to DAC
block to set the idle current.
Shutdown Input. Drive logic low to place the device in shutdown mode. Drive logic high for normal
operation.
Bias Circuit DC Supply Voltage. Bypass to ground using configuration in the typical operating
circuit.
