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MRF49XA-I/T 数据表(PDF) 49 Page - Microchip Technology

部件名 MRF49XA-I/T
功能描述  ISM Band Sub-GHz RF Transceiver
PDF  102 Pages
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制造商  MICROCHIP [Microchip Technology]
网页  http://www.microchip.com
标志 MICROCHIP - Microchip Technology

MRF49XA-I/T 数据表(HTML) 49 Page - Microchip Technology

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© 2009-2011 Microchip Technology Inc.
Preliminary
DS70590C-page 49
MRF49XA
3.6
Crystal Selection Guidelines
The crystal oscillator of MRF49XA requires a 10 MHz
Parallel mode crystal. The circuit contains an
integrated load capacitor in order to minimize the
external
component
count.
The
internal
load
capacitance value is programmable from 8.5 pF –
16 pF in 0.5 pF steps. With appropriate PCB layout, the
total load capacitance value can be 10 pF – 20 pF, so a
variety of crystal types can be used.
When the total load capacitance is not more than 20 pF,
and a worst case 7 pF Shunt Capacitance (CS) value is
expected for the crystal, the oscillator is able to start-up
with any crystal having less than 100
Ω Equivalent
Series Loss Resistance (ESR). However, the low CS
and ESR values ensure the faster oscillator start-up.
The Crystal Frequency (fref) is used as the reference of
the PLL, which generates the Local Oscillator
Frequency (fLO). Therefore, fLO is directly proportional to
fref. The accuracy requirements for production tolerance,
temperature drift and aging can thus be determined from
the maximum allowable local oscillator frequency error.
Whenever a low-frequency error is essential for the
application, it is possible to “pull” the crystal to the
accurate frequency by changing the load capacitor
value. The widest pulling range can be achieved if the
nominal required load capacitance of the crystal is in
the “midrange”; for example, 16 pF. The “pull-ability” of
the crystal is defined by its Motional Capacitance (Cm)
and shunt capacitance.
FIGURE 3-5:
MAXIMUM CRYSTAL TOLERANCES INCLUDING TEMPERATURE AND AGING (ppm)
30
45
60
75
90
105
120
433 MHz
15
30
50
70
80
100
100
868 MHz
8
15
25
30405060
915 MHz
8
15
25
30405050
Deviation [± kHz]
Bit Rate: 9.6 kbps
30
45
60
75
90
105
120
433 MHz
20
30
50
70
90
100
100
868 MHz
10
20
25
30
40
50
60
915 MHz
10
15
25
30
40
50
50
Deviation [± kHz]
Bit Rate: 2.4 kbps
30
45
60
75
90
105
120
433 MHz
Do Not Use
5
20
30
50
75
75
868 MHz
Do Not Use
3
10
20
25
30
40
915 MHz
Do Not Use
3
10
15
25
30
40
Deviation [± kHz]
Bit Rate: 38.4 kbps
105
120
135
150
165
180
195
433 MHz
Do Not Use
3
20
30
50
70
80
868 MHz
Do Not Use
Do Not Use
10
20
25
35
45
915 MHz
Do Not Use
Do Not Use
10
15
25
30
40
Deviation [± kHz]
Bit Rate: 115.2 kbps



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