BC41B143A-DS-003PC Datasheet, PDF (50/94 Pages) List of Unclassifed Manufacturers – BlueCore 4-ROM Plug-n-Go Single Chip Bluetooth v2.0 + EDR System

Device Terminal Descriptions
Frequency
Initial Tolerance
Pullability
Min
8MHz
-
-
Typ
16MHz
±25ppm
±20ppm/pF
Max
32MHz
-
-
Table 10.3: Crystal Specification
The BlueCore4-ROM Plug-n-Go driver circuit is a transconductance amplifier. A voltage at XTAL_IN generates a
current at XTAL_OUT. The value of transconductance is variable and may be set for optimum performance.
10.3.2 Load Capacitance
For resonance at the correct frequency the crystal should be loaded with its specified load capacitance, which is
defined for the crystal. This is the total capacitance across the crystal viewed from its terminals. BlueCore4-ROM
Plug-n-Go provides some of this load with the capacitors C_trim and C_int. The remainder should be from the external
capacitors labelled C_t1 and C_t2. C_t1 should be three times the value of C_t2 for best noise performance. This maximises
the signal swing, hence, slew rate at XTAL_IN (to which all on-chip clocks are referred). Crystal load capacitance, C_l
is calculated with Equation 10.1:
C_I
=
C_int
+
C_trim
2
+
C_t1•C_t2
C_t1 + C_t2
Equation 10.1: Load Capacitance
Where:
C_trim = 3.4pF nominal (mid-range setting)
C_int = 1.5pF
Note:
C_int does not include the crystal internal self capacitance; it is the driver self capacitance.
BC41B143A-ds-003Pc
Advance Information
© Cambridge Silicon Radio Limited 2005
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