CC2531F128 Datasheet, PDF (25/35 Pages) Texas Instruments – A USB-Enabled System-On-Chip Solution for 2.4-GHz IEEE 802.15.4 and ZigBee Applications

CC2531F128, CC2531F256
www.ti.com
SWRS086A – SEPTEMBER 2009 – REVISED JUNE 2010
Table 2. Overview of External Components (Excluding Supply Decoupling
Capacitors)
Component
C21
C31
C41
C221
C231
C251
C252
C253
C261
C262
C321
C331
C401
L252
L261
R21
R31
R32
R301
Description
USB D– decoupling
USB D+ decoupling
Decoupling capacitor for USB pad power supply
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
Part of the RF matching network
32-kHz xtal-loading capacitor
32-kHz xtal-loading capacitor
Decoupling capacitor for the internal digital regulator
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
Resistor used for internal biasing
Value
47 pF
47 pF
10 pF
27 pF
27 pF
18 pF
1 pF
2.2 pF
18 pF
1 pF
15 pF
15 pF
1 mF
2 nH
2 nH
33 Ω
33 Ω
1.5 kΩ
56 kΩ
Input/Output Matching
When using an unbalanced antenna such as a monopole, a balun should be used to optimize performance. The
balun can be implemented using low-cost discrete inductors and capacitors. The recommended balun shown
consists of C262, L261, C252, and L252.
If a balanced antenna such as a folded dipole is used, the balun can be omitted.
Crystal
An external 32-MHz crystal, XTAL1, with two loading capacitors (C221 and C231) is used for the 32-MHz crystal
oscillator. See the 32-MHz Crystal Oscillator section for details. The load capacitance seen by the 32-MHz
crystal is given by:
C_L =
1
1
1
+ C_parasitic
+
C₂₂₁ C₂₃₁
(1)
XTAL2 is an optional 32.768-kHz crystal, with two loading capacitors (C321 and C331) used for the 32.768-kHz
crystal oscillator. The 32.768-kHz crystal oscillator is used in applications where both low sleep-current
consumption and accurate wake-up times are needed. The load capacitance seen by the 32.768-kHz crystal is
given by:
C_L = ₁ ¹ ₁ + C_parasitic
+
C₃₂₁ C₃₃₁
(2)
A series resistor may be used to comply with the ESR requirement.
On-Chip 1.8-V Voltage-Regulator Decoupling
The 1.8-V on-chip voltage regulator supplies the 1.8-V digital logic. This regulator requires a decoupling capacitor
(C401) for stable operation.
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