Theory of Operation
17
The New Focus Picomotor usually comes with a high reliability RJ-11 plug.
The mating receptacle for printed circuit board mounting is available from
many sources:
3.8
EMC Considerations
The 8712 was designed for use as a component of a larger system, and
incorporates several design features to improve the overall system’s EMC
performance:
•
Output filter: Both PULSE OUTPUT and PULSE RETURN incorporate
inductor capacitor T-networks. The T-networks largely attenuate both
ESD pulses entering the 8712 and microprocessor clock harmonics
leaving the 8712. The bottom of the T-network connects to the 8712
ground.
•
Frame ground connection: Several pins connect frame ground to the
internal 8712 ground via a 0.1-
μF capacitor. This connection is close
to
that of the output T-filters mentioned above. Microprocessor clock
harmonics are shunted back to internal ground by the T-network. ESD
energy is shunted to frame ground when the FRAME GROUND pins are
connected to the customers frame ground. This connection must be low
inductance (i.e. short and wide).
•
Optically coupled control interface: As mentioned above, optical
coupling is used to break the low frequency ground loop inherent in
locating the 8712 close to its power source. Further benefits in the EMC
aspect of system design are the reduction in I/O coupling to the more
sensitive control section of most systems, and the reduction of controller
clock harmonics coupling to the 8712 output.
Additional protection may be needed to provide acceptable EMC
performance of a system incorporating the 8712. An additional set of output
T-filter networks close to the Picomotor connector and equipment bulkhead
will shunt ESD energy before it enters the system. A common-mode power-
line filter will reduce radiation/conduction of switching-power-supply
harmonics.
Attention to printed circuit board layout details, as mentioned in previous
sections, will go a long way to ensuring success at the EMC test lab.
Make
Model
Digi-Key #
Hirose (side entry)
TM5RJ3-44
H9081-ND
