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A8520E24A91 – User’s Manual
Release Date 02/27/12
Figure 6 Mounting the module in a corner
Figure 7 Mounting the module along an edge
3.5.
Power Supply Considerations
Noise on the power supply line reduces the sensitivity of a receiver and can modulate onto a
transmitters signal, both of which causes a degradation of link quality and hence a reduction in
range.
The A8520E24A91 radio modules have integral noise reduction in the supply line from pins 33
(Vdd) and 32 (IOVdd), consisting of ferrite beads and decoupling capacitances. This
arrangement will take care of most supply voltage noise. For optimal performance in particular
noisy environments (switching regulators, motor controls, etc.) it may be necessary to add
additional noise reduction means, which can consist of a low noise LDO or additional LC
filtering.
Pin 4 (AVdd_CC259x) is connected to the modules internal supply line after the ferrite bead and
decoupling capacitors and can be used to probe the noise at module level. The noise level
measured on pin 4 should not exceed 150mVpp when in transmit or receive mode, it may
however exceed this value when not in either transmit or receive mode or in the transition itself
(i.e. it may exceed this if synchronized to the XPAEN and XLNAEN signals.
If the level measured is exceeding the above limit means should be taken to ensure maximum
range:
Add decoupling capacitance to pin 4 (AVdd_CC259x), 1uF to 2.2uF ceramic capacitor is
suggested (do not use Tantalum).
Add decoupling capacitance to pin 33 (AVdd), 1uF to 2.2uF ceramic capacitor is
suggested (do not use Tantalum).
Add a low noise LDO in the supply line to pin 33 (AVdd) (the TPS731xx low Dropout
Regulator from TI is recommended).
