Rainbow Electronics ATA5812 - Manual (Page 7)

7
ATA5811/ATA5812 [Preliminary]
4689B–RKE–04/04
Typical Car or Sensor Base-station Application
Figure 5. Typical RKE Car or Sensor Base-station Application, 433.92 MHz
Figure 5 shows a typical 433.92 MHz V
CC
= 4.75 V to 5.25 V RKE car or sensor base-
station application. The external components are 12 capacitors, 1 resistor, 4 inductors, a
SAW filter and a crystal. C
1
and C
3
to C
4
are 68 nF voltage supply blocking capacitors.
C
2
and C
12
are 2.2 µF supply blocking capacitors for the internal voltage regulators. C
5
is a 10 nF supply blocking capacitor. C
6
is a 15 nF fixed capacitor used for the internal
quasi peak detector and for the highpass frequency of the data filter. C
7
to C
11
are RF
matching capacitors in the range of 1 pF to 33 pF. L
2
to L
4
are matching inductors of
about 5.6 nH to 56 nH. A load capacitor for the crystal of 9 pF is integrated. R
1
is typi-
cally 22 k
Ω
and sets the output power at RF_OUT to about 10 dBm. Since a quarter
wave or PCB antenna, which has high efficiency and wide band operation, is typically
used here, it is recommended to use a SAW filter to achieve high sensitivity in case of
powerful out-of-band blockers. L
1
, C
10
and C
9
together form a lowpass filter, which is
needed to filter out the harmonics in the transmitted signal to meet regulations. An inter-
nally regulated voltage at pin VSOUT can be used in case the microcontroller only
supports 3.3
V operation, a blocking capacitor with a value of C
12
= 2.2 µF has to be
connected to VSOUT in any case.
AVC
C
RX
_
T
X
1
RX
_
T
X
2
DV
CC
VS2 VS1
VSINT
VAU
X
PWR
_
O
N
N_RESET
XT
AL
1
XTAL2
CLK
T
EST
1
DEM_OUT
T1
IRQ
RSSI
CDEM
CS
SCK
SDI_TMDI
SDO_TMDO
VSO
U
T
NC
RX
_
A
CT
IV
E
RF_IN
NC
NC
R_PWR
RF_OUT
433_N868
PWR_H
NC
NC
NC
NC
NC
NC NC T
EST
2
NC
NC NC
VCC
VSS
AVCC
20 m
m
x
0.
4 m
m
50
Ω
connector
Microcontroller
ATA5811/ATA5812
C
1
C
2
C
9
C
8
C
10
C
5
C
7 C
6
C
3
L
2
C
4
R
1
13.25311 MHz
RF
OUT
VCC = 4.75 V..5.25 V
SAW-Filter
L
1
L
3
L
4
C
11
C
12
T2 T3 T4 T5