Datasheet

Page 17 of 161
nRF8001 Product Specification
Revision 1.2
6.2.2 16 MHz crystal oscillator
The 16 MHz crystal oscillator is designed for use with an AT-cut quartz crystal in parallel resonant mode.
To achieve correct oscillation frequency, the load capacitance must match the specification in the crystal
datasheet. Figure 4.
shows how the crystal is connected to the 16 MHz crystal oscillator.
Figure 4. Circuit diagram of the nRF8001 16 MHz crystal oscillator
The load capacitance is the total capacitance seen by the crystal across its terminals and is given by:
C1 and C2 are ceramic SMD capacitors connected between each crystal terminal and ground. C_pcb1
and C_pcb2 are stray capacitances on the PCB. C_pin is the pin input capacitance on the XC1 and XC2
pins, typically 1 pF. The load capacitance C1 and C2 should be of the same value.
6.2.3 External 16 MHz clock
nRF8001 may be used with an external 16 MHz reference applied to the XC1 pin instead of a 16 MHz
crystal. An input amplitude of 0.8 V peak-to-peak or higher is recommended to achieve low current
consumption. Keep the maximum voltage level so that all peak voltages are under the recommended
maximum operating conditions as specified in Chapter 11 on page 33
. The external signal must have an
accuracy of 40 ppm or better. The XC1 pin loads the external application’s crystal oscillator with
approximately 1 pF in addition to PCB routing. Do not connect the XC2 pin.
C1 C2
16 MHz
crystal
XC1 XC2
pinCpcbCCC
pinCpcbCCC
CC
CC
load
C
_2_2'2
_1_1'1
)'2'1(
)'2'1(




