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TMC4670 Datasheet PRELIMINARY • IC Version V0.99 | Document Revision V0.91 • 2016-Nov-09
means PWM = OFF. For operation, the centered PWM mode must be set on by setting the PWM mode to
7. A single bit controls the Space vector PWM (SVPWM). For 3-phase PMSM the SVPWM = ON gives more
effective voltage. Nevertheless, for some applications it makes sense to switch the SVPWM = OFF to keep
the star point voltage of a motor almost at rest.
3.8.1 PWM Polarites
This PWM polarities register PWM_POLARITES controls the polarities of the control signals. Positive polarity
for gate control means 1 represents ON and 0 represents OFF. The gate control signal polarities are
individually programmable for low side gate control and for low side gate control. The PWM polarities
register controls the polarity of other control signals as well.
3.8.2 PWM frequency
The PWM counter maximul length register PWM_MAXCNT controls the PWM frequency. For a clock
frequency fCLK = 25MHz, the PWM frequency fPWM[Hz] = is (4.0 * fCLK[Hz]) / (PWM_MAXCNT + 1). With
fCLK = 25MHz and power-on reset (POR) default of PWM_MAXCNT=3999 the PWM frequency is fPWM
= 25kHz. The PWM frequency fPWM is recommended to be in the range of 25kHz to 200kHz by setting
PWM_MAXCNT between 3999 to 499.
Note
The PWM frequency can be changed any time also during motion.
3.8.3 PWM Resolution
The base resolution of the PWM is 12 bit internally mapped to 16 bit range. MAX_PWMCNT=4095 gives the
full resolution of 12 bit with
≈
25kHz w/ fCLK=25MHz. MAX_PWMCNT=2047 results in 11 bit resolution but
with
≈
50kHz w/ fCLK=25MHz. So the PWM_MAXCNT defines the PWM frequency but effects the resolution
of the PWM.
3.8.4 PWM Modes
The power-on reset (POR) default of the PWM is OFF. The standard PWM scheme is the centered PWM.
Passive Breaking and Free Wheeling Modes are available on demand. Please refer [
?] concerning the
settings.
3.8.5 Brake-Before-Make (BBM)
One register controls BBM time for the high side. One register controls BBM time for the low side. The
BBM times are programmable in 10ns steps. The BBM time can be set to zero for gate drivers that have
there own integrated BBM timers.
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