Technosoft 2018
18
iPOS4808 VX Technical Reference
Figure 3.5 Recommended spacing for horizontal mounting, worst case: non-metallic, closed box
3.2. Motherboard PCB Design
The iPOS4808 drive, when plugged vertically into the recommended mating connector, has the
following PCB footprint:
40.15
2.4
Figure 3.6 PCB footprint of mating connector
It is recommended to use a multi-layer PCB for the motherboard, in order to have enough room for
routing all the 98 pins of the iPOS4808. Using a 2-layer PCB is possible when some of the
iPOS4808 pins remain un-connected.
Below is a list of recommendations for the PCB design of the motherboard:
•
Motor supply and motor outputs: use islands / areas of copper to escape connector area;
this will maximize current capability. When using simple tracks, use at least 200mil cross
section (150mil track width for 1oz/ft
2
copper thickness) – for iPOS4808.
•
Motor supply and ground return tracks between iPOS4808 and the nearby V
MOT
decoupling
capacitor are to be considered as EMI sources, and kept to a minimum length.
•
Place the decoupling capacitors on V
MOT
and V
LOG
(see also 0. Power Supply Connection)
as close as physically possible to the iPOS4808, to minimize EM radiated emissions. For
un-shielded applications (no metallic box) and typical EMC regulations, the spacing
between iPOS4808 and capacitors must be less than 3 centimeters.
•
In multi-axis applications (multiple iPOS4808 drives on the same motherboard), it is
preferable to have a separate decoupling capacitor for each drive’s V
MOT
. For V
LOG
it is
acceptable to share one decoupling capacitor for two drives.
•
For stringent EMI requirements, it may be necessary to add common-mode filtering on the
motor and/or logic supply inputs. Be sure to use 3-phase EMC filters, not 2-phase filters, in
order to fulfill the basic requirement of zero common-mode current through the filter. This
is necessary because the ground negative return is shared between V
MOT
and V
LOG
.
•
Motor outputs shall be routed with parallel traces, and minimizing the loop area between
these tracks. Avoid placing components above or below the motor output tracks, as these
components may become effective antennas radiating EMI. If possible, route all 4 motor
outputs in strip-line configuration (above or below a ground plane).
•
For stringent EMI requirements, it may be necessary to add common-mode inductors on
the motor outputs. Place these filters near the iPOS4808, not near the external connector,
to reduce radiation from the PCB tracks.
•
Motor outputs must be separated from any nearby track (on the same layer) by a guard
ring / track / area connected to ground. It is recommended to use the same guarding
precaution also for tracks on nearby layers, i.e. use intermediate guard layer(s) connected
to ground. The motor outputs must be treated as first source of noise on the motherboard.
Second source of noise is the current flow between each iPOS4808 and it’s decoupling
V
MOT
capacitor.
•
For best EMC performance, it is strongly recommended to provide an un-interrupted ground
plane on one of the inner layers.
•
All GND pins of the iPOS4808
are galvanically connected together on-board the iPOS4808.
If the motherboard provides an uninterrupted ground plane, it is recommended to connect
all GND pins to the ground plane, and use the ground plane to distribute GND wherever
needed. If the motherboard does not provide an uninterrupted ground plane, it is best to
use each GND pin for it’s intended purpose, as described in par. 3.4.3. This will create local
“star point” ground connection on-board each iPOS4808. For a multi-axis motherboard with
one common power supply for all motors, each motor power supply return track shall be
routed separately for each iPOS4808, and star-point connected at the power supply
terminal.
