MRF24J40_08 Datasheet, PDF (10/152 Pages) Microchip Technology – IEEE 802.15.4™ 2.4 GHz RF Transceiver

MRF24J40
2.4 Power and Ground Pins
Recommended bypass capacitors are listed in
Table 2-2. VDD pins 1 and 31 require two bypass
capacitors to ensure sufficient bypass decoupling. Min-
imize trace length from the VDD pin to the bypass
capacitors and make them as short as possible.
TABLE 2-2:
VDD Pin
1
4
5
21
31
32
35
37
39
RECOMMENDED BYPASS
CAPACITOR VALUES
Bypass Capacitor
47 pF and 0.01 μF
47 pF
0.1 μF
0.01 μF
47 pF and 0.01 μF
47 pF
47 pF
0.01 μF
1 μF
2.5 20 MHz Main Oscillator
The 20 MHz main oscillator provides the main
frequency (MAINCLK) signal to internal RF, baseband
and MAC circuitry. An external 20 MHz quartz crystal is
connected to the OSC1 and OSC2 pins as shown in
Figure 2-2. The crystal parameters are listed in
Table 2-3.
TABLE 2-3: 20 MHz CRYSTAL
PARAMETERS⁽¹⁾
Parameter
Value
Frequency
Frequency Tolerance at 25°C
Frequency Stability over Operating
Temperature Range
20 MHz
±20 ppm⁽²⁾
±20 ppm⁽²⁾
Mode
Fundamental
Load Capacitance
15-20 pF
ESR
80Ω max.
Note 1: These values are for design guidance only.
2: IEEE 802.15.4™ Standard specifies
transmitted center frequency tolerance
shall be ±40 ppm maximum.
FIGURE 2-2:
CL2
CL1
20 MHz MAIN
OSCILLATOR CRYSTAL
CIRCUIT
OSC2
20 MHz
X1
Main Oscillator
OSC1
2.6 Phase Lock Loop
The Phase Lock Loop (PLL) circuitry requires one
external capacitor connected to pin 40 (LCAP). The
recommended value is 100 pF. The PCB layout around
the capacitor and pin 40 should be designed carefully
such as to minimize interference to the PLL.
2.7 32 kHz External Crystal Oscillator
The 32 kHz external crystal oscillator provides one of two
Sleep clock (SLPCLK) frequencies to Sleep mode
counters. The Sleep mode counters time the Beacon
Interval (BI) and inactive period for a beacon-enabled
device and the Sleep interval for a nonbeacon-enabled
device. Refer to Section 3.15 “Sleep” for more
information.
The SLPCLK frequency is selectable between the 32
kHz external crystal oscillator or 100 kHz internal oscil-
lator. The 32 kHz external crystal oscillator provides
better frequency accuracy and stability than the 100
kHz internal oscillator. An external 32 kHz tuning fork
crystal is connected to the LPOSC1 and LPOSC2 pins,
as shown in Figure 2-3. The crystal parameters are
listed in Table 2-4.
TABLE 2-4: 32 kHz CRYSTAL
PARAMETERS⁽¹⁾
Parameter
Value
Frequency
32.768 kHz
Frequency Tolerance
±20 ppm
Load Capacitance
12.5 pF
ESR
70 kΩ max.
Note 1: These values are for design guidance only.
DS39776B-page 8
Preliminary
© 2008 Microchip Technology Inc.