Datasheet

Page 47 of 161
nRF8001 Product Specification
Revision 1.2
14.2 External 16 MHz clock
The nRF8001 may be used with an external 16 MHz clock applied to the XC1 pin. An input amplitude of
0.8 V peak-to-peak or higher is recommended to achieve low current consumption and a good signal-to-
noise ratio. The DC level is not important as long as the applied signal never rises above
VDD or drops
below
VSS. The XC1 pin will load the microcontrollers crystal with approximately 5 pF in addition to PCB
routing.
XC2 shall not be connected.
Note: A frequency accuracy of ± 40 ppm or better is required to get a functional radio link.
14.3 32.768 kHz crystal specification requirements
For reliable operation the 32.768 kHz crystal load capacitance, shunt capacitance, Equivalent Series
Resistance (ESR) and drive level must comply with the specifications listed in Table 19.
Table 19. 32.768 kHz crystal specification
To achieve correct oscillation frequency it is important that the load capacitance matches the specification
in the crystal datasheet. The load capacitance 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 the P0.0 and P0.1 pins of
the nRF8001 (typically 3 pF when configured as crystal pins). C1 and C2 should be of the same value, or
as close as possible. 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 0.5 s for a crystal with 9 pF load capacitance, 1 pF shunt
capacitance and an ESR of 50 k.
Symbol Parameter (condition) Notes Min Nom Max Units
F
XO32
32.768 kHz crystal frequency 32.768 kHz
f Tolerance
1
1. Frequency accuracy including tolerance at 25 ºC, temperature drift, aging and crystal loading
0
500 ppm
C
L
Load capacitance 9 12.5 pF
C
0
Equivalent parallel capacitance 1 2 pF
ESR Equivalent series resistance 50 80 k
P
D
Drive level 1 µW
C
L
C
1
C
2

C
1
C
2

---------------------
=
C
1
C
1
C
PCB1
C
PIN
++=
C
2
C
2
C
PCB2
C
PIN
++=