VIA Technologies EPIA-M Mini-ITX Manual de usuario descargar pdf (Pagina 15)

Mini-ITX Power Solutions Andrei Bulucea

Automotive Solutions Ituner Networks

DC-DC converters - 15 - Automotive Applications

ITPS Mode of Operation

Switched and un-switched battery goes into J1 via F1 (6A polyfuse). D2 and D3 provide reverse

and forward protection. The power is controlled by U2 microcontroller (PIC 12C508). GPIO 1

controls the 12 V in via the Q1 and Q2 (power P-channel FET). GPIO 2/4 are connected to the

Motherboard button (open drain) to turn OFF/ON the board. For more information on how the

power sequencer works, see the “Power Sequencing” chapter.

The output of Q2 goes into U4, and the 12 V/5V LDO LM-1084-12 into your DC-DC converter.

For more information on regulation, see “Regulation for Automotive Use”

Microcode and timing charts are available below.

Fig 2.1, ITOS photo (board size 120x16mm)

Regulation for Automotive Use

While many DC-DC converters can operate directly from a 12 V source, it is a good idea to

regulate the car 12 V output prior to applying it to the input of the DC-DC converter. Cars do have

voltage regulation. However, in some instances the voltage can spike up as high as 18-20 V,

activating over-voltage protection circuitry on the DC-DC converter as well as on your

motherboard.

Since a typical car voltage is in between 13.4-14.5 V, an LDO (low dropout) regulator can be

used to provide a clean 12 V output. Proper heat sinks must be used with LDO circuits. The

power dissipation on the LDO regulator is

= (V

-V

out

) x I

where V

is the input voltage, V

out

is the 12 V regulated voltage, and I

is the total current

consumed by your mini-ITX board. Here is an example:

= (13.8 V – 12.0 V) x 2A = 3.6 V,

indicating that you do need a heat sink! Look up www.digi-key.com for more information on TO-

220 heat sinks. A good heat sink model used in the ITPS power sequencer project is Digi-Key

HS104-2-ND – TO220 PWR CLR 1.45” 10 W.

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VIA Technologies EPIA-M Mini-ITX Manual de usuario Pagina 15