MSK4360 Datasheet, PDF (5/8 Pages) M.S. Kennedy Corporation – 10 AMP, 55V, 3 PHASE MOSFET BRUSHLESS MOTOR CONTROLLER

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.
REGULATED VOLTAGE FILTER CAPACITORS
It is recommended that about 10 μF of capacitance (tantalum electrolytic) for bypassing the + and -15V regulated outputs be
placed as close to the module pins as practical. Adding ceramic bypass capacitors of about 0.1 μF to 1 μF will aid in suppressing noise
transients.
GENERAL LAYOUT
Good PC layout techniques are a must. Ground plane for the analog circuitry must be used and should be tied back to the SIG GND.
Ground plane for the power circuitry should be tied back to the V+ RTN pin, pin 16. Pin 16 should be connected to pin 10 external to the
hybrid by a single thick trace. This will connect the two ground planes together.
LOW POWER STARTUP
When starting up a system utilizing the MSK4360 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 +8 volts positive peak, or -8 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.NFor compensation calculations, refer to the block diagram for all
information to determine the amplifier gain for loop gain calculations.
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8548-74 Rev. N 12/14