NL865H2 Hardware Design Guide
1VV0301616 Rev. 7
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26
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2020-04-20
4.4.3.
Power Supply PCB layout Guidelines
As seen on the electrical design guidelines the power supply shall have a low ESR capacitor
on the output to cut the current peaks and a protection diode on the input to protect the
supply from spikes and polarity inversion. The placement of these components is crucial for
the correct working of the circuitry. A misplaced component can be useless or can even
decrease the power supply performance.
•
The Bypass low ESR capacitor must be placed close to the Telit NL865H2-W1
power input pads or in the case the power supply is a switching type it can be
placed close to the inductor to cut the ripple provided the PCB trace from the
capacitor to the NL865H2-W1 is wide enough to ensure a dropless connection
even during the 500mA current peaks.
•
The protection diode must be placed close to the input connector where the
power source is drained.
•
The PCB traces connecting the Switching output to the inductor and the
switching diode must be kept as short as possible by placing the inductor and
the diode very close to the power switching IC (only for switching power supply).
This is done in order to reduce the radiated field (noise) at the switching
frequency (100-500 kHz usually)
•
The use of a good common ground plane is suggested.
•
The placement of the power supply on the board should be done in such a way
to guarantee that the high current return paths in the ground plane are not
overlapped to any noise sensitive circuitry as the microphone amplifier/buffer or
earphone amplifier.
•
The power supply input cables should be kept separate from noise sensitive
lines such as microphone/earphone cables.
•
The insertion of EMI filter on VBATT pins is suggested in those designs where
antenna is placed close to battery or supply lines.
•
A ferrite bead like Murata BLM18EG101TN1 or Taiyo Yuden P/N
FBMH1608HM101 can be used for this purpose.
RTC Bypass out
The NL865H2-W1 module is provided by an internal RTC section but its reference supply
is VBATT.So, in order to maintain active the RTC programming, VBATT should not be
removed.
