N27 Hardware User Guide
Chapter 4 Application Interfaces
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Figure 4-1 Recommended power design
Power Supply
N27 Module
D1
C1
C2
C3
C4
Close to the pin of the module
VBAT
Test point
I_max
C5
Schematic guidelines
The maximum input voltage for the module is 4.3 V and the typical value is 3.6V.
The protection voltage at D1 should not exceed the maximum input voltage the module can bear.
Place TVS close to the input of the power supply to clamp the surge voltage before it enters
back-end circuits. Therefore, the back-end components and the module are protected.
A large bypass tantalum capacitor (220 μF or 100 μF) or aluminum capacitor (470 μF or 1000μF)
is expected at C1 to reduce voltage drops during bursts. Its safe operating voltage should be
larger than 1.5 times the voltage across the power supply.
Place a bypass capacitor of low-ESR close to the module to filter out high-frequency jamming
from the power supply.
PCB Layout
Place an ESR capacitor at the output of the power supply to absorb surge current. Place a TVS diode
at the input of VBAT to protect back-end components. Follow the rules below in the power supply
design:
TVS diodes dissipate the transient pulse power during a surge and can handle a peak pulse
current of dozens or more than 100 A. they have a fast response time.
Place the TVS as close to the interface as possible to ensure that the surge voltage can be
clamped before the pulse is coupled to the neighbor traces.
Place bypass capacitors close to the power pin of the module to filter out the high-frequency
signal from the power supply.
Ensure that the width of PCB traces for VBAT circuits allows 3A current and ensure no obvious
decrease of loop voltages.
The trace should be 3 mm in width at least and the ground plane should be as complete as
possible. The traces of the power circuit should be as short and wide as possible.
