Datasheet

PRELIMINARY PRODUCT SPECIFICATION
nRF24L01 Single Chip 2.4 GHz Radio Transceiver
Nordic Semiconductor ASA - Vestre Rosten 81, N-7075 Tiller, Norway - Phone [phone] - Fax [phone]
Revision: 1.2 Page 31 of 39 March 2006
nRF24L01 sharing crystal with a micro controller.
When using a micro controller to drive the crystal reference input XC1 of the
nRF24L01 transceiver some rules must be followed.
Crystal parameters:
When the micro controller drives the nRF24L01 clock input, the requirement of load
capacitance C
L
is set by the micro controller only. The frequency accuracy of ±60
ppm is still required to get a functional radio link. The nRF24L01 will load the crystal
by 0.5pF at XC1 in addition to the PBC routing.
Input crystal amplitude & Current consumption
The input signal should not have amplitudes exceeding any rail voltage, but any DC-
voltage within this is OK. Exceeding rail voltage will excite the ESD structure and the
radio performance is degraded below specification. If testing the nRF24L01 with a RF
source with no DC offset as the reference source, the input signal will go below the
ground level, which is not acceptable.
XC1
XO_OUT
Amplitude
controlled
current source
Buffer:
Sine to
full swing
Current starved
inverter:
XOSC core
XC2
Vdd
Vss
Vdd
Vss
ESD
ESD
Figure 12 Principle of crystal oscillator
The nRF24L01 crystal oscillator is amplitude regulated. To achieve low current
consumption and also good signal-to-noise ratio when using an external clock, it is
recommended to use an input signal larger than 0.4 V-peak. When clocked externally,
XC2 is not used and can be left as an open pin.