MSK4363_15 Datasheet, PDF (5/7 Pages) M.S. Kennedy Corporation – 75 Volt Motor Supply Voltage

APPLICATION NOTES CONTINUED
BUS VOLTAGE FILTER CAPACITORS
The size and placement of the capacitors for the DC bus has a direct bearing on the amount of noise filtered and also on the size and
duration of the voltage spikes seen by the bridge. What is being created is a series RLC tuned circuit with a resonant frequency that
is seen as a damped ringing every time one of the transistors switches. For the resistance, wire resistance, power supply impedance
and capacitor ESR all add up for the equivalent lumped resistance in the circuit. The inductance can be figured at about 30 nH per
inch from the power supply. Any voltage spikes are on top of the bus voltage and the back EMF from the motor. All this must be
taken into account when designing and laying out the system. If everything has been minimized, there is another solution. A second
capacitance between 5 and 10 times the first capacitor and it should either have some ESR or a resistor can be added in series with
the second capacitor to help damp the voltage spikes.
Be careful of the ripple current in all the capacitors. Excessive ripple current, beyond what the capacitors can handle, will destroy
the capacitors.
±15VIN FILTER CAPACITORS
It is recommended that about 10 μF of capacitance (tantalum electrolytic) for bypassing the + and -15V inputs be placed as close to
the module pins as practical. Adding ceramic bypass capacitors of about 0.1 μF or 1 μF will aid in suppressing noise transients.
GENERAL LAYOUT
Good PC layout techniques are important. Ground planes for the analog circuitry must be used and should be tied back to the small
signal grounds, pins 17,18,33 and 34. The high power grounds (RTN) pins 1,2 and 3 get tied back to the small signal ground
internally. DO NOT connect these grounds externally. A ground loop will result.
LOW POWER STARTUP
When starting up a system utilizing the MSK 4363 for the first time, there are a few things to keep in mind. First, because of the small
size of the module, short circuiting the output phases either to ground or the DC bus will destroy the bridge. The current limiting and
control only works for current actually flowing through the bridge. The current sense resistor has to see the current in order for the
electronics to control it. If possible, for startup use a lower voltage and lower current power supply to test out connections and the
low current stability. With a limited current supply, even if the controller locks up, the dissipation will be limited. By observing the
E/A OUT pin which is the error amp output, much can be found out about the health and stability of the system. An even waveform
with some rounded triangle wave should be observed. As current goes up, the DC component of the waveform should move up or
down. At full current (with a regular supply) the waveform should not exceed +4 volts positive peak, or -4 volts negative peak.
Some audible noise will be heard which will be the commutation frequency. If the motor squeals, there is instability and power should
be removed immediately unless power dissipation isn't excessive due to limited supply current. For compensation calculations, refer
to the block diagram for all information to determine the amplifier gain for loop gain calculations. For the power up sequence, ±15
volts should be powered at the same time or before the V+ voltage is applied.
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8548-106 Rev. P 10/13