THE DESIGN CYCLE
We need to lay down top and bottom ground plane
layers to complete some of the component’s ground
paths. The ground planes will also do double duty and act
as a heatsink for VR1. Laying down ground planes will also
help eliminate unwanted electrical noise. Screenshot 3 is
Screenshot 2 with a bottom-layer ground plane. As you
can see, we brought the bottom-layer ground plane up to
the ZG2100M’s no-trace zone and no further. All of the
vias and holes that were designated to connect electrically
to the bottom-layer ground plane are under the bottom-layer ground plane’s domain.
All of the holes and vias that are programmed
to connect to the bottom-layer
ground plane are also programmed
to connect electrically to the
top-side ground plane. This has been
done to accommodate ground
connections for top-side components
that have been programmed to meld
to the plane using a thermal pad.
This is the case for Q1 and Q2, and
the thermal pad electrical
connections can clearly be seen in
The top-layer ground plane
has been applied in Screenshot 5.
The top-layer ground plane is
electrically connected to the
bottom-layer ground plane by way
of holes and vias that are
programmed to electrically connect
on both planes. With the addition
of our top-layer ground plane, we
now have more than adequate
heatsinking area for VR1, and the
NUD3105s have a ground path.
Note that we didn’t bring the
top-layer ground plane into the
ZG2100M’s air space.
All that’s left to do is check,
double check, and triple check our
PCB work. Once we’re sure we’re
ready to take the plunge, the
ExpressPCB PCB file will be
transferred to the ExpressPCB server
for entry into their daily production
release the magic smoke.
I let the cat out of the bag when I told you about
being able to power the ZeroG - PIC24FJ128GA006
Trainer with a 3. 3 volt wall wart. Anyway, I’m happy to
report that the finished board shown in Photo 4
responded to the MPLAB ICD3 and no magic smoke
was released. Just to make sure things were good inside
of the PIC24FJ128GA006, I wrote a bit of code to
toggle the LEDs attached to Q1 and Q2. A finger on the
case of the ZG2100M didn’t detect any significant heat
signatures and all of the voltage points reported in at
+ 3. 3 volts.
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A COUPLE OF
I received the PCB you see
grinning from edge to edge in Photo
3. This is crunch time. Any trace or
layer mistakes we made in the initial
design run will shine though with
some of them having the ability to
April 2010 73