MSK1695 MSK, MSK1695 Datasheet - Page 5

• Manufacturer Part Number: MSK1695
• Description: BRUSHLESS MOTOR SPEED CONTROLLER
• Manufacturer: MSK

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.
LOW POWER STARTUP
When starting up a system utilizing the MSK 1695 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 limit sensor has to see the current in
order for the electronics to control it. If possible, for startup use a 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.
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PRELIMINARY Rev. B 11/06