14
\$\begingroup\$

I am designing a little mezzanine PCB that uses Hirose DF12 connectors to connect to the motherboard.

Stacker PCB

Four different voltages are delivered to this PCB: ±10v, 3.3v, 48v (and ground). They go through one of the DF12 connectors.

Which of these two ways is the preferred way to lay out the power and ground connections on the connector?

First way: Each power has its own ground. Power Connections

Second way: Single set of ground shared by all power. Power Connections

\$\endgroup\$
5
  • 2
    \$\begingroup\$ It's best to use alternating PWR, GND arrangement. This reduces the loop area and so reduces EMI emissions. IDE and other interfaces do the same. \$\endgroup\$ Jan 22, 2013 at 17:03
  • 1
    \$\begingroup\$ I must ask: what program do you use to render these awesome 3D boards? \$\endgroup\$ Jan 22, 2013 at 18:01
  • 1
    \$\begingroup\$ @SimpleCoder - I use Altium. \$\endgroup\$ Jan 22, 2013 at 18:05
  • 1
    \$\begingroup\$ @SimpleCoder - Sadly, it's Windows only. \$\endgroup\$ Jan 22, 2013 at 18:13
  • \$\begingroup\$ And freakin' expensive :\. I think my school has a multi-seat license for it, though, so I might get a chance to use it. \$\endgroup\$ Jan 22, 2013 at 18:15

2 Answers 2

7
\$\begingroup\$

I would keep grounds separate especially if you have sensitive analog and ONLY tie them at the power supply, or at least at only one place if not at the power supply.

Also, I'd physically separate powers in your connector by one pin position. For example on #2, put a space between 3.3V and +10V (pins 36 and 37).

I usually lay out my connectors based on where the circuit components are physically located relative to the connector. Pay attention to return currents and try to keep them from crossing each other, if you've tied all the grounds together on your mezzanine. With segregated grounds you mitigate this but then have to make sure your signals aren't crossing the splits.

\$\endgroup\$
7
\$\begingroup\$

Arrange your power/ground pins such that if you reverse the connection end-for-end or plug a cable into the wrong connector you won't short power to ground.

\$\endgroup\$
2
  • \$\begingroup\$ Connectors in the picture seem to be keyed, so this wouldn't be such an issue. \$\endgroup\$ Jan 22, 2013 at 20:45
  • 6
    \$\begingroup\$ Depending upon the design of the supply and gauge of the cable, shorting power to ground will often be preferable to reversing power and ground. If the supply has any sort of overcurrent protection, shorting power and ground will often safely keep everything shut down. By contrast, reversing power and ground may turn all of one's chips into masses of molten slag. \$\endgroup\$
    – supercat
    Jan 22, 2013 at 21:04

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.