CC2540F128_14 Datasheet, PDF (25/36 Pages) Texas Instruments – 2.4-GHz Bluetooth low energy System-on-Chip

CC2540F128, CC2540F256
www.ti.com
SWRS084F – OCTOBER 2010 – REVISED JUNE 2013
Table 2. Overview of External Components (Excluding Supply Decoupling Capacitors) (continued)
Component
C401
L251
L252
L253
L261
R301
Description
Decoupling capacitor for the internal digital regulator
Part of the RF matching network
Part of the RF matching network
Part of the RF matching network
Part of the RF matching network
Resistor used for internal biasing
Value
1 µF
2 nH
1 nH
3 nH
2 nH
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.
Crystal
An external 32-MHz crystal, XTAL1, with two loading capacitors (C221 and C231) is used for the 32-MHz crystal
oscillator. See 32-MHz CRYSTAL OSCILLATOR 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 very 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.
Power-Supply Decoupling and Filtering
Proper power-supply decoupling must be used for optimum performance. The placement and size of the
decoupling capacitors and the power supply filtering are very important to achieve the best performance in an
application. TI provides a compact reference design that should be followed very closely.
References
1. Bluetooth® Core Technical Specification document, version 4.0
http://www.bluetooth.com/SiteCollectionDocuments/Core_V40.zip
2. CC253x System-on-Chip Solution for 2.4-GHz IEEE 802.15.4 and ZigBee^® Applications/CC2540 System-on-
Chip Solution for 2.4-GHz Bluetooth low energy Applications (SWRU191)
3. Current Savings in CC254x Using the TPS62730 (SWRA365)
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