bc41b143a07 ETC-unknow, bc41b143a07 Datasheet - Page 57

• Manufacturer Part Number: bc41b143a07
• Description: Single Chip Bluetooth
• Manufacturer: ETC-unknow

9.3.3
BlueCore4-ROM enables frequency adjustments to be made. This feature is typically used to remove initial tolerance
frequency errors associated with the crystal. Frequency trim is achieved by adjusting the crystal load capacitance with
on-chip trim capacitors, C
calculated thus:
There are two C
appear in series so each least significant bit (LSB) increment of frequency trim presents a load across the crystal of
55fF.
The frequency trim is described by Equation 9.6.
Where Fx is the crystal frequency and pullability is a crystal parameter with units of ppm/pF. Total trim range is 63
times the value above.
If not specified, the pullability of a crystal may be calculated from its motional capacitance with Equation 9.7.
Where:
Note:
CS-101564-DSP12
C
C
It is a Bluetooth requirement that the frequency is always within ±20ppm. The trim range should be sufficient to
pull the crystal within ±5ppm of the exact frequency. This leaves a margin of ±15ppm for frequency drift with ageing
and temperature. A crystal with an ageing and temperature drift specification of better than ±15ppm is required.
0
m
= Crystal self capacitance (shunt capacitance)
= Crystal motional capacitance (series branch capacitance in crystal model). See Figure 9.4.
Frequency Trim
trim
capacitors, which are both connected to ground. When viewed from the crystal terminals, they
trim
. The value of C
∆
C
F
( )
Equation 9.5: Trim Capacitance
F
trim
X
Equation 9.6: Frequency Trim
X
trim
=
=
Equation 9.7: Pullability
110
∂
pullabilit
Production Information
∂
( )
is set by a 6-bit word in PSKEY_ANA_FTRIM (0x1f6). Its value is
© CSR plc 2003-2007
F
( )
C
X
fF
×
=
PSKEY
y
F
X
×
•
55
2
(
×
C
_
10
I
C
+
AN A
m
−
C
3
0
(
ppm
)
_
2
FT R IM
/
LSB
)
Device Terminal Descriptions
Page 57 of 97