MA838 Datasheet, PDF (9/13 Pages) Zarlink Semiconductor Inc – SINGLE PHASE PULSE WIDTH MODULATION WAVEFORM GENERATOR

MA838
Control Register Programming
The control register should only be programmed once the
initialisation register contains the basic operating parameters
of the MA838.
As with the initialisation register, control register data is
loaded into the three 8-bit temporary registers R0 - R2. When
all the data has been loaded into these registers it is transferred
into the 24-bit control register by writing to the dummy register
R3. It is recommended that all three temporary registers are
updated before writing to R3 in order to ensure that a conformal
set of data is transferred to the control register for execution.
Overmodulation selection
The overmodulation bit OM is, in effect, the ninth bit (MSB) of
the amplitude word. When active (i.e., high) the output waveform
will be controlled in the 100% to 200% range by the amplitude
word.
The percentage amplitude control is now given by:
Overmodulated Amplitude = A_POWER + 100%
where A_POWER = the power amplitude
Fig. 11 Temporary register R0
Fig. 12 Temporary register R1
Power frequency selection
The power frequency is selected as a proportion of the
power frequency range (defined in the initialisation register) by
the 12-bit power frequency select word, PFS, allowing the
power frequency to be defined in 4096 equal steps. As the PFS
word spans the two temporary registers R0 and R1 it is
therefore essential, when changing the power frequency, that
both these registers are updated before writing to R3.
The power frequency (f_POWER) is given by:
f_POWER
=^fRANGE
4096
x
pfs
Fig. 13 Voltage waveforms as seen at the motor terminals,
showing the effect of setting the overmodulation bit
Amplitude selection
The power waveform amplitude is determined by scaling
the amplitude of the waveform samples stored in the internal
ROM by the value of the 8-bit amplitude select word (AMP).
The percentage amplitude control is given by:
A
Power Amplitude, A_POWER = ₂₅₅ x 100%
where A = decimal value of AMP.
where pfs = decimal value of the 12-bit PFS word and f_RANGE
= power frequency range set in the initialisation register.
Output inhibit selection
When active (i.e., Iow) the output inhibit bit INH sets all the
PWM outputs to the off (low) state. No other internal operation
of the device is affected. When the inhibit is released the PWM
outputs continue immediately. Note that as the inhibit is asserted
after the pulse deletion and pulse delay circuits, pulses shorter
than the normal minimum pulse width may be produced initially.
Fig.14 Temporary register R2
8