User Manual

© 2011 Microchip Technology Inc. Preliminary DS00000A-page 11
MRF24J40MC
2.0 CIRCUIT DESCRIPTION
The MRF24J40MC is a 2.4 GHz IEEE Std. 802.15.4™
compliant surface mount module with integrated crystal,
internal voltage regulator, matching circuitry, power
amplifier, low noise amplifier with 50Ω external antenna
connector.
The MRF24J40MC module interfaces to many popular
Microchip PIC microcontrollers through a 4-wire SPI
Interface, interrupt, wake, reset, power and ground. An
example application schematic is illustrated in
Figure 2-1.
Serial communications and register definitions for the
MRF24J40MC module are documented in the
“MRF24J40 IEEE 802.15.4™ 2.4 GHz RF Transceiver
Data Sheet” (DS39776). Refer to the “MRF24J40 Data
Sheet” for specific serial interface protocol and register
definitions. Also, see Section 1.3, Operation for specific
register settings that are unique to the MRF24J40MC
module.
2.1 External Antenna
The MRF24J40MC module has a 50Ω ultra miniature
coaxial (U.FL) connector to connect to an external 2.4
GHz antenna. The choice of antenna is limited to the
antenna types the module has been tested with. Refer
to the respective country in Section 3.0, Regulatory
Approval for a list of tested and approved antenna
types that may be used with the MRF24J40MC
module.
2.2 Module Schematic
A schematic diagram of the module is illustrated in
Figure 2-2 and the Bill of Materials (BOM) is shown in
Table 2-1.
The MRF24J40MC module is based on the Microchip
Technology MRF24J40 IEEE 802.15.4™ 2.4 GHz RF
Transceiver IC (U6). The Serial I/O (SCK, SDI, SDO
and CS
), RESET, WAKE and INT pins are brought out
to the module pins. The SDO signal is tri-state buffered
by U7 to solve a silicon errata, where the SDO signal
does not release to a high-impedance state, after the
CS
pin returns to its inactive state.
Crystal, X1, is a 20 MHz crystal with a frequency
tolerance of ±10 ppm @ 25°C to meet the IEEE Std.
802.15.4 symbol rate tolerance of ±40 ppm.
A balun is formed by components: L11, L12, L13, C25,
C27 and C31. L12 is also a pull-up for the RFP and
RFN pins on the MRF24J40. C25 also acts as a DC
block capacitor. RF switches, U1 and U2, switch
between the power amplifier, U3, when transmitting
and low noise amplifier, U2, when receiving. A
band-pass filter FL1 is placed after the PA U3 to reduce
harmonics. The remaining passive components
provide bias and decoupling.
FIGURE 2-1: MRF24J40MC APPLICATION SCHEMATIC