Datasheet

Page 46 of 161
nRF8001 Product Specification
Revision 1.2
14 External component requirements and recommendations
The tables in this chapter specify the crystal parameters that are required for nRF8001 to function and
meet the
Bluetooth low energy specification. Table 18. specifies the requirements for the 16 MHz crystal.
Table 19. on page 47
specifies the requirements for the 32.768 kHz crystal.
14.1 16 MHz crystal oscillator specification requirements
The 16 MHz crystal oscillator is designed to be used with an AT-cut quartz crystal in parallel resonant
mode. To achieve correct oscillation frequency it is very important that the load capacitance matches the
specification in the crystal datasheet. The load capacitance C
L
, as specified in the crystal datasheet, is the
total capacitance seen by the crystal across its terminals:
C1 and C2 are ceramic SMD capacitors connected between each crystal terminal and VSS, C
PCB1
and
C
PCB2
are stray capacitances on the PCB, while C
PIN
is the input capacitance on nRF8001’s XC1 and XC2
pins (typically 5 pF). C1 and C2 should be of the same value, or as close as possible.
To ensure a functional radio link the frequency accuracy must be ± 40 ppm or better. The initial tolerance of
the crystal, drift over temperature, aging and frequency pulling due to incorrect load capacitance must all
be taken into account. For reliable operation the crystal parameters must comply with the specifications in
Table 18.
Table 18. 16 MHz crystal oscillator specifications
It is recommended to use a crystal with lower than maximum ESR if the load capacitance and/or shunt
capacitance is high. This will give faster start-up and lower current consumption.
The start-up time is typically less than 1 ms for a crystal with 9 pF load capacitance and an ESR
specification of 50 . This value is valid for crystals in a 3.2 x 2.5 mm can. If you use the smallest crystal
cans (like 2.0 x 2.5 mm), pay particular attention to the startup time of the crystal. These crystals have a
longer startup than crystals in larger cans. To make sure the startup time < 1.5 ms use a crystal for load
capacitance of 6 pF. A low load capacitance will reduce both startup time and current consumption. For
more details regarding how to measure the startup of a specific crystal, please see the
nAN24-13
application note.
Symbol Parameter (condition) Notes Min Nom Max Units
F
XO16
16 MHz crystal frequency 16 MHz
f Tolerance
1
1. Frequency offset at 25 ºC, temperature drift, aging and crystal loading
± 40 ppm
C
L
Load capacitance 6 9 16 pF
C
0
Equivalent parallel capacitance 3 7 pF
L
S
Equivalent series inductance
2
2. Startup time from power down is dependant on the Ls parameter
30 50 mH
ESR Equivalent series resistance 50 100 
P
D
Drive level 100 µW
PINPCB
PINPCB
LOAD
CCCC
CCCC
CC
CC
C





22
'
2
11
'
1
'
2
'
1
'
2
'
1