MAX7030 MAXIM [Maxim Integrated Products], MAX7030 Datasheet - Page 16

• Manufacturer Part Number: MAX7030
• Description: Low-Cost, 315MHz, 345MHz, and 433.92MHz ASK Transceiver with Fractional-N PLL
• Manufacturer: MAXIM [Maxim Integrated Products]

connect AV
cases, bypass DV
0.01µF and 220pF capacitors and bypass AV
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 to the
respective pins as possible.
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.
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 PC board 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 PC board para-
sitics. 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 reference frequency higher.
Low-Cost, 315MHz, 345MHz, and 433.92MHz
ASK Transceiver with Fractional-N PLL
16
______________________________________________________________________________________
Transmit/
DD
, PAV
DD
DD
, HV
Crystal Oscillator (XTAL)
Receive Antenna Switch
, and DV
IN
, and PAV
DD
together. In both
DD
to GND with
DD
to
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
C
C
C
C
When the crystal is loaded as specified, i.e.,
C
f
p
P
m
CASE
SPEC
LOAD
LOAD
is the amount the crystal frequency is pulled in ppm.
=
is the motional capacitance of the crystal.
C
TOP VIEW
2
m
is the specified load capacitance.
is the case capacitance.
is the actual load capacitance.
= C



C
SPEC
25
26
27
28
29
30
31
32
CASE
24
1
, the frequency pulling equals zero.
23
2
+
1
C
22
3
LOAD
THIN QFN
MAX7030
21
4
Pin Configuration
20
5
−
C
19
6
CASE
18
7
17
1
+
8
C
SPEC
16
15
14
13
12
11
10
9



x
10
6