User's Guide

UL865 Hardware User Guide
1VV0301050 Rev 2 – 2013-10-09
The principal guidelines for the Power Supply Design embrace three different design
steps:
the electrical design
the thermal design
the PCB layout.
The electrical design of the power supply depends strongly from 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
The desired output for the power supply is 3.8V, hence there's 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 shall 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 the UL865, 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 should be inserted close to the power input, in order to save the
UL865 from power polarity inversion.