HE920 Hardware User Guide
1vv0301014 Rev.9 – 2014-01-23
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Page 35 of 84
5.2.
General Design Rules
The principal guidelines for the Power Supply Design embrace three different design steps:
the electrical design
the thermal design
the PCB layout
5.2.1.
Electrical Design Guidelines
The electrical design of the power supply depends strongly on the power source where this
power is drained. We will distinguish them into three categories:
+5V input (typically PC internal regulator output)
+12V input (typically automotive)
battery
5.2.1.1.
+ 5V Input Source Power Supply Design Guidelines
The desired output for the power supply is 3.8V, hence there is not a big
difference between the input source and the desired output and a linear regulator
can be used. A switching power supply will not be suited because of the low
drop-out requirements.
When using a linear regulator, a proper heat sink must be provided in order to
dissipate the power generated.
A Bypass low ESR capacitor of adequate capacity must be provided in order to
cut the current absorption peaks close to HE920, a 100μF tantalum capacitor is
usually suited.
Make sure the low ESR capacitor on the power supply output (usually a tantalum
one) is rated at least 10V.
A protection diode must be inserted close to the power input, in order to save
HE920 from power polarity inversion.
