only and connect AVDD, PAVDD, and DVDD together.
In both cases, bypass DVDD, HVIN, and PAVDD to
GND with 0.01µF and 220pF capacitors and bypass
AVDD to GND with 0.1µF and 220pF capacitors.
Bypass T/R, ENABLE, DATA, and AGC0-2 with 10pF
capacitors to GND. Place all bypass capacitors as
close as possible to the respective pins.
Transmit/
Receive
Antenna Switch
The MAX7030 features an internal SPST RF switch that,
when combined with a few external components, allows
the transmit and receive pins to share a common
antenna (see the
Typical Application Circuit)
. In receive
mode, the switch is open and the power amplifier is
shut down, presenting a high impedance to minimize
the loading of the LNA. In transmit mode, the switch
closes to complete a resonant tank circuit at the PA
output and forms an RF short at the input to the LNA. In
this mode, the external passive components couple the
output of the PA to the antenna and protect the LNA
input from strong transmitted signals.
The switch state is controlled by the T/R pin (pin 22).
Drive T/R high to put the device in transmit mode; drive
T/R low to put the device in receive mode.
Control Interface Considerations
When operating the MAX7030 with a +4.5V to +5.5V
supply voltage, the AGC0, ACG1, AGC2, DATA,
ENABLE and T/R pins may be driven by a microcon-
troller with either 3V or 5V interface logic levels. When
operating the MAX7030 with a +2.1V to +3.6V supply,
the microcontroller must produce logic levels which
conform to the V
IH
and V
IL
specifications in the
DC
Electrical Characteristics
for the MAX7030.
Crystal Oscillator (XTAL)
The XTAL oscillator in the MAX7030 is designed to pre-
sent a capacitance of approximately 3pF between the
XTAL1 and XTAL2 pins. In most cases, this corre-
sponds to a 4.5pF load capacitance applied to the
external crystal when typical PCB parasitics are added.
It is very important to use a crystal with a load
capacitance that is equal to the capacitance of the
MAX7030 crystal oscillator plus PCB parasitics. If a
crystal designed to oscillate with a different load
capacitance is used, the crystal is pulled away from its
stated operating frequency, introducing an error in the
reference frequency. Crystals designed to operate with
higher differential load capacitance always pull the ref-
erence frequency higher.
In actuality, the oscillator pulls every crystal. The crys-
tal’s natural frequency is really below its specified fre-
quency, but when loaded with the specified load
capacitance, the crystal is pulled and oscillates at its
specified frequency. This pulling is already accounted
for in the specification of the load capacitance.
Additional pulling can be calculated if the electrical
parameters of the crystal are known. The frequency
pulling is given by:
where:
f
p
is the amount the crystal frequency is pulled in ppm.
C
m
is the motional capacitance of the crystal.
C
CASE
is the case capacitance.
C
SPEC
is the specified load capacitance.
C
LOAD
is the actual load capacitance.
When the crystal is loaded as specified, i.e.,
C
LOAD
= C
SPEC
, the frequency pulling equals zero.
N.C.
N.C.
