Carrier board design guidelines (SOM)

Info Box Applies to Naon Applies to Maya Applies to Lizard Applies to Diva

The information here provided are preliminary and subject to change.

Introduction

This page provides useful information and resources to system designers in order to design an efficient host board for DAVE SOM module.

This guidelines are provided with the goal to help designers to design compliant systems with DAVE module and they cover schematics and PCB aspects.

Basics Guidelines

In this section we want to analyze basics HW guidelines valid for all DAVE SOMs.

Schematics

• Check mirroring and pinout for every connector on the board
• Check for TX and RX lines
• Add series resitor as interface needs (see interface details)
• TBD

PCB

PCB Tecnology

Use a PCB tecnology as advised in the following table

	Min	Typ	Max
Layers(number)	4	6	-
Power Layers	2	2	-
Clearence(mils)	4	6	-
Vias hole (mechanical)	0,3		-
Minimum number of via for each power signal layer changes	2	3	-
Minimum number of via for each power signal SOM connector pin	1	2	-
Component package size	0402	0603	-
PCB Height(mm)	1,4	1,6	-

• If vias less than minimum advised size are used, take care to maintain an adeguate number of via when you change layer on each power signal.
  
• PCB heights less than minimum advised can produce PCB heating and mechanical issues.

PCB Basics Guidelins

• Avoid stubs
• Isolate clock and HI-SPEED signal (differential lines i.e.) for at least two times trace width or gap for differential lines
• Avoid voids on planes

Interfaces Guidelines

This section provides guidelines for the most used interfaces on DAVE's SOMs module. Please refer to SOM's detailed pages for specific additional information.

ETHERNET 10/100

Schematics

• If LAN connector with integrated magnetic are used:
  • predispose some protection diodes on ethernet lines
  • Connect connector shield to an adeguate GND or shield Plane

PCB

'	Min	Typ	Max
Differential Impedance(ohm)	76	95	114
Common Mode Impedance	46,75	55	63,25
Gap between TX and RX lines	2xseparation	4xseparation	-
Gap between other signal	2xseparation	2xseparation	-
Intra pair matching(mils)	-	240	-
TX and RX via mismatch	0	0	1

• If LAN connector with integrated magnetic are used:
  • do not route traces under the connettor, neither on opposite side
  • place filter diode near connector
  • place others signals far from connector.
  • Connect connector shield to an adeguate GND or shield Plane or Copper through numerous vias if necessary
• If on board magnetic are used
  • adeguately isolate system GND from magnetic connector side
• try to match as best as possible each differential pair
• no TX and RX matching required