TMC603A Datasheet, PDF (23/44 Pages) TRINAMIC Motion Control GmbH & Co. KG. – Three phase motor driver with BLDC back EMF commutation hallFX™ and current sensing

TMC603A DATA SHEET (V. 1.15 / 2009-Nov-19)
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5.4.1 Adjusting the hallFX™ spike suppression time
hallFX™ needs two minimum motor- and application-specific adjustments: The switched capacitor
clock frequency and the spike suppression time should be adapted. Both can easily be deducted from
basic application parameters and are not very critical. The SCCLK frequency should be matched to
the chopper frequency of the system and the maximum motor velocity. The spike suppression time
needs to be adapted to the desired maximum motor velocity.
Calculating the commutation frequency f_COM of the motor:
S_RPM is the rotation velocity in RPM
n_POLE is the pole count of the actual motor, or the double of the number of pole pairs
The spike suppression time can be chosen as high, as the commutation frequency required for
maximum motor velocity allows. As a thumb rule, we take half of this time to have enough spare.
Example:
Given a 4 pole motor operating at 4000 RPM:
C_SUP = 6.25nF. The nearest value is 6.8nF.
5.4.2 Adjusting the hallFX™ filter frequency
The filter block needs to separate the motors’ back EMF from the chopper pulses. Thus, the target is,
to filter away as much commutation noise as possible, while maintaining as much of the back EMF
signal as possible. Therefore, we need to find a cut-off frequency in between the chopper frequency
and the electrical frequency of the motor. Since we do not want to change the frequency within the
application, we use the nominal or maximum motor velocity to calculate its electrical frequency. The
chopper frequency is given by the system, typically about 20 kHz.
The electrical frequency of the motor is:
Since the filter has a logarithmic behavior, as a thumb rule we can make a logarithmic mean-value as
follows:
With the cut-off frequency being about 1/390 of the switched capacitor clock frequency f_SCCLK the
following results as a thumb rule:
The result shall be checked against minimum limit of 250 kHz and maximum limit of 4 MHz, however,
the actual frequency is quite uncritical and can be varied in a wide range.
Example:
Given a 4 pole motor operating at 4000 RPM with a 20 kHz chopper frequency:
f_EL = 133 Hz
f_CUTOFF = 1.6 kHz
f_SCCLK = 0.64 MHz
The result is well within the limits, however, the frequency in a practical application can be
chosen between 300 kHz and 1.5 MHz.
Copyright © 2009 TRINAMIC Motion Control GmbH & Co. KG