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AMIS30512C5122G Datasheet, PDF (17/30 Pages) ON Semiconductor – Micro-Stepping Motor Driver | |||
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AMISâ30512
Speed and Load Angle Output
The SLAâpin provides an output voltage that indicates the
level of the Backâe.m.f. voltage of the motor. This
Backâe.m.f. voltage is sampled during every soâcalled âcoil
ICOIL
current zero crossingsâ. Per coil, two zeroâcurrent positions
exist per electrical period, yielding in total four zeroâcurrent
observation points per electrical period.
V BEMF
t
ZOOM
Previous
Microâstep
Coil Current Zero Crossing
Next
Microâstep
ICOIL
Current Decay
Zero Current
t
VCOIL
VBB
Voltage Transient
VBEMF
t
Figure 12. Principle of Bemf Measurement
Because of the relatively high recirculation currents in the
coil during current decay, the coil voltage VCOIL shows a
transient behavior. As this transient is not always desired in
application software, two operating modes can be selected
by means of the bit <SLAT> (see âSLAâtransparencyâ in
Table 15: SPI Control Register 2). The SLA pin shows in
âtransparent modeâ full visibility of the voltage transient
behavior. This allows a sanityâcheck of the speedâsetting
versus motor operation and characteristics and supply
voltage levels. If the bit âSLATâ is cleared, then only the
voltage samples at the end of each coil current zero crossing
are visible on the SLAâpin. Because the transient behavior
of the coil voltage is not visible any more, this mode
generates smoother Back e.m.f. input for postâprocessing,
e.g. by software.
In order to bring the sampled Back e.m.f. to a descent
output level (0 to 5 V), the sampled coil voltage VCOIL is
divided by 2 or by 4. This divider is set through an SPI bit
<SLAG>. (Table 15: SPI Control Register 2)
The following drawing illustrates the operation of the
SLAâpin and the transparencyâbit. âPWMshâ and
âIcoil=0â are internal signals that define together with SLAT
the sampling and hold moments of the coil voltage.
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