CC2538_15 Datasheet, PDF (20/33 Pages) Texas Instruments – Powerful Wireless Microcontroller System-On-Chip

CC2538
SWRS096D – DECEMBER 2012 – REVISED APRIL 2015
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Table 6-1. Overview of External Components (Excluding Supply Decoupling
Capacitors)
Component
C21
C31
C341
C351
C371
C381
C382
C372
C441
C451
C561
C321
C281
L372
L381
R21
R31
R32
R281
R421
Description
USB D– decoupling
USB D+ decoupling
32-MHz xtal-loading capacitor
32-MHz xtal-loading capacitor
Part of the RF matching network
Part of the RF matching network
Part of the RF matching network
Part of the RF matching network
32-kHz xtal-loading capacitor
32-kHz xtal-loading capacitor
Decoupling capacitor for the internal digital regulator
Decoupling capacitor for the internal digital regulator
Filter capacitor for reset line
Part of the RF matching network
Part of the RF matching network
USB D– series resistor
USB D+ series resistor
USB D+ pullup resistor to signal full-speed device presence
Filter resistor for reset line
Resistor used for internal biasing
Value
47 pF
47 pF
12 pF
12 pF
18 pF
18 pF
1 pF
1 pF
22 pF
22 pF
1 µF
1 µF
1 nF
2 nH
2 nH
33 Ω
33 Ω
1.5 kΩ
2.2 Ω
56 kΩ
6.1 Input, Output Matching
When using an unbalanced antenna such as a monopole, use a balun to optimize performance. One can
implement the balun using low-cost, discrete inductors and capacitors. The recommended balun shown in
Figure 6-1 consists of L372, C372, C382 and L381.
If a balanced antenna such as a folded dipole is used, omit the balun.
6.2 Crystal
The 32-MHz crystal oscillator uses an external 32-MHz crystal, XTAL1, with two loading capacitors (C341
and C351). See the 32-MHz Crystal Oscillator section for details. Calculate the load capacitance across
the 32-MHz crystal by Equation 1.
C_L =
1
11
+ C_parasitic
+
C₃₄₁ C₃₅₁
(1)
XTAL2 is an optional 32.768-kHz crystal, with two loading capacitors (C441 and C451) used for the
32.768-kHz crystal oscillator. Use the 32.768-kHz crystal oscillator in applications where both low sleep-
current consumption and accurate wake-up times are needed. Calculate the load capacitance across the
32.768-kHz crystal by Equation 2.
C_L =
1
1
1
+ C_parasitic
+
C₄₄₁ C₄₅₁
(2)
Use a series resistor, if necessary, to comply with the ESR requirement.
20
Applications, Implementation, and Layout
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