Data Sheet
Revision 2.0 Page 60 of 74
nRF24L01 Product Specification
Figure 28. Principle of crystal oscillator
The nRF24L01 crystal oscillator is amplitude regulated. It is recommended to use an input signal larger
than 0.4V-peak to achieve low current consumption and good signal-to-noise ratio when using an external
clock. XC2 is not used and can be left as an open pin when clocked externally.
10.4 PCB layout and decoupling guidelines
A well designed PCB is necessary to achieve good RF performance. A poor layout can lead to loss of per-
formance or functionality. A fully qualified RF-layout for the nRF24L01 and its surrounding components,
including matching networks, can be downloaded from www.nordicsemi.no
.
A PCB with a minimum of two layers including a ground plane is recommended for optimum performance.
The nRF24L01 DC supply voltage should be decoupled as close as possible to the VDD pins with high per-
formance RF capacitors, see Table 26. on page 69
. It is preferable to mount a large surface mount capaci-
tor (for example, 4.7μF ceramic) in parallel with the smaller value capacitors. The nRF24L01 supply
voltage should be filtered and routed separately from the supply voltages of any digital circuitry.
Long power supply lines on the PCB should be avoided. All device grounds, VDD connections and VDD
bypass capacitors must be connected as close as possible to the nRF24L01 IC. For a PCB with a topside
RF ground plane, the VSS pins should be connected directly to the ground plane. For a PCB with a bottom
ground plane, the best technique is to have via holes as close as possible to the VSS pads. A minimum of
one via hole should be used for each VSS pin.
Full swing digital data or control signals should not be routed close to the crystal or the power supply lines.
The exposed die attach pad is a ground pad connected to the IC substrate die ground and is intentionally
not used in our layouts. It is recommended to keep it unconnected.
XC1
XO_OUT
Amplitude
controlled
current source
Buffer:
Sine to
full swing
Current starved
inverter:
XOSC core
XC2
Vdd
Vss
Vdd
Vss
ESD
ESD