EM351_12 Datasheet, PDF (223/244 Pages) Silicon Laboratories – High-Performance, Integrated ZigBee/802.15.4 System-on-Chip

EM351 / EM357
18 Typical Application
Figure 18-1 illustrates the typical application circuit, and Table 18-1 contains an example Bill of Materials
(BOM) for the off-chip components required by the EM35x.
Note: The circuit shown in Figure 18-1 is for example purposes only, and the BOM is for budgetary quotes
only. For a complete reference design, please download one of the latest Silicon Labs hardware reference
designs from the Silicon Labs website (www.silabs.com/zigbee-support).
The Balun provides an impedance transformation from the antenna to the EM35x for both Tx and Rx modes.
L1 tunes the impedance presented to the RF port for maximum transmit power and receive sensitivity.
The harmonic filter (L2, L3, C5, C6 and C9) provides additional suppression of the second harmonic, which
increases the margin over the FCC limit.
The 24 MHz crystal Y1 with loading capacitors is required and provides the high-frequency crystal oscillator
source for the EM35x’s main system clock. The 32.768 kHz crystal with loading capacitors generates a highly
accurate low-frequency crystal oscillator for use with peripherals, but it is not mandatory as the low-
frequency internal RC oscillator can be used.
Loading capacitance and ESR (C1 and R3) provides stability for the internal 1.8 V regulator.
Loading capacitance C2 provides stability for the internal 1.25 V regulator, no ESR is required because it is
contained within the chip.
Resistor R1 reduces the operating voltage of the flash memory, this reduces current consumption and
improves sensitivity by 1 dB when compared to not using it.
Various decoupling capacitors are required, these should be placed as close to their corresponding pins as
possible. For values and locations see one of the latest reference designs.
An antenna matched to 50 Ω is required.
18-1
Final
120-035X-000 Rev. 1.2