CC2540T Datasheet, PDF (26/37 Pages) Texas Instruments – Extended Industrial Temperature Bluetooth Smart Wireless MCU

CC2540T
SWRS172A – JULY 2014 – REVISED NOVEMBER 2015
www.ti.com
Table 6-1. Overview of External Components (Excluding Supply Decoupling Capacitors)
COMPONENT
C221
C231
C251
C252
C253
C261
C262
C321
C331
C401
L251
L252
L253
L261
R301
DESCRIPTION
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
Part of the RF matching network
Part of the RF matching network
Resistor used for internal biasing
VALUE
12 pF
12 pF
18 pF
1 pF
1 pF
18 pF
1 pF
15 pF
15 pF
1 µF
2 nH
1 nH
3 nH
2 nH
56 kΩ
6.2 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.
6.3 Crystal
An external 32-MHz crystal, XTAL1, with two loading capacitors (C221 and C231) is used for the 32-MHz
crystal oscillator. See Section 4.10 for details. The load capacitance seen by the 32-MHz crystal is given
by Equation 1:
C_L =
1
11
+ 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 Equation 2:
C_L =
1
1
1
+ C_parasitic
C₃₂₁ ⁺ C₃₃₁
(2)
A series resistor may be used to comply with the ESR requirement.
6.4 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.
6.5 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 (see
Section 6.6).
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Applications, Implementation, and Layout
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