Pin configuration, Receive – Rainbow Electronics MAX7030 User Manual
Page 16
connect AV
DD
, PAV
DD
, and DV
DD
together. In both
cases, bypass DV
DD
, HV
IN
, and PAV
DD
to GND with
0.01µF and 220pF capacitors and bypass AV
DD
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 to the
respective pins as possible.
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.
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 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.
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.
f
C
C
C
C
C
x
P
m
CASE
LOAD
CASE
SPEC
=
+
−
+
2
1
1
10
6
MAX7030
Low-Cost, 315MHz, 345MHz, and 433.92MHz
ASK Transceiver with Fractional-N PLL
16
______________________________________________________________________________________
32
31
30
29
28
27
26
9
10
11
12
13
14
15
18
19
20
21
22
23
24
7
6
5
4
3
2
1
MAX7030
THIN QFN
TOP VIEW
ROUT
PAV
DD
TX/RX1
TX/RX2
PAOUT
AV
DD
LNAIN
8
LNASRC
XTAL2
XTAL1
AGC0
AGC1
AGC2
HV
IN
DV
DD
25
N.C.
D
ATA
ENABLE
T/R
N.C.
DF
OP+
DS+
17
DS-
PDMIN
IFIN+
16
PDMAX
IFIN-
MIXOUT
MIXIN-
MIXIN+
LNAOUT
Pin Configuration