User's Manual

© 2009 Microchip Technology Inc. Preliminary DS70599B-page 7
MRF24J40MB
2.0 CIRCUIT DESCRIPTION
The MRF24J40MB is a complete 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 and PCB
antenna. The MRF24J40MB module interfaces to many
popular Microchip PIC microcontrollers via a 4-wire
serial SPI interface, interrupt, wake, Reset, power and
ground. Data communications with the MRF24J40MB
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.
2.1 Schematic
A schematic diagram of the module is shown in
Figure 2-1 and the Bill of Materials (BOM) is shown in
Table 2-1.
The MRF24J40MB module is based on the Microchip
Technology MRF24J40 IEEE 802.15.4™ 2.4 GHz RF
Transceiver IC (U1). 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 IC7 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: L1, L3, C2 and C3.
L2 is an RF choke and pull-up for the RFP and RFN
pins on the MRF24J40. C4 is a DC block capacitor. RF
switches, IC2 and IC4, switch between the power
amplifier, IC3, when transmitting and low noise
amplifier, IC5, when receiving. A low-pass filter is
formed by components: L10, L11, C31, C32 and C36.
The remaining passive components provide bias and
decoupling.