User Manual

AND8399/D
http://onsemi.com
26
By sampling the SLA−pin as given in Figure 26, one
samples the SLA−pin at the correct moment to make sure
that the real BEMF is measured. An offset will be detected
as well as a stall condition. By sampling the SLA−pin at the
right moment, temperature effect will be eliminated (see
High Temperature).
Microcontroller without ADC
To implement above flowcharts one needs to use a
microcontroller with ADC. In some cases this ADC is not
available. A simple way to enable stall detection in this case
is by using a comparator.
COMP
Vdd
R
1
R
2
IO
Micro−
Controller
GND
Vcc
AMIS−305xx
SLA
GND
Vdd
R
pull−up
R
3
Figure 27. Stall Detection with Comparator
R1 and R2 set the threshold level. R3 adds a hysteresis to
avoid toggling caused by noise. The microcontroller can
check if the SLA voltage is above or below the threshold
level by monitoring the digital IO pin.
The way to implement stall detection stays similar. The
only difference with the flowchart in Figure 26 is that
instead of sampling the SLA voltage with an ADC, the status
of the IO pin is checked to determine if SLA voltage is above
or below the threshold level. The moment the status of this
digital IO is checked stays the same.
If a variable threshold is needed, R1 and R2 can be
replaced by a potentiometer or even by a digital
potentiometer controlled by the microcontroller (see
www.onsemi.com
for Digital Programmable
Potentiometers and Comparators).
R3 is not mandatory but is advised to avoid toggling cause
by noise on the SLA−pin. If R3 is not used, a low−pass filter
should be added to the SLA−pin (see also Figure 20).
Working with a digital IO can also be beneficial to offload
the CPU of the microcontroller. Sampling an analog value
could take some time. Monitoring a digital pin gives low
CPU load.
Conclusion
Implementing the best stall, steploss or torque adaptive
algorithm is useless if the SLA−pin of AMIS−305xx is not
used properly. By following some simple guidelines, the
SLA−pin can be used in a correct and reliable way.
References
Ref 1: AMIS−305xx datasheet (www.onsemi.com)
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