EM357-RTR datasheet(220/240 Pages) ETC2

220 / 240 page

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 Ember Reference Designs from the

Ember website (www.ember.com).

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

120-035X-000D

Preliminary

EM357-RTR 数据表(PDF) 220 Page - List of Unclassifed Manufacturers