a4980klp-t Allegro MicroSystems, Inc., a4980klp-t Datasheet - Page 15

• Manufacturer Part Number: a4980klp-t
• Description: Automotive, Programmable Stepper Driver
• Manufacturer: Allegro MicroSystems, Inc.

A4980
current to rise to the limit quickly and the PWM current control
to activate. However, when a motor is running at speed the back
EMF, generated by the speed of the magnetic poles in the motor
passing the phase windings, acts against the supply voltage and
reduces the rise time of the phase current. Therefore the PWM
current control takes longer to activate. Assuming a constant step
rate, this results in fewer PWM cycles for each step of the motor.
The A4980 uses this difference to detect a motor changing from
continuous stepping to stalled. Two PWM counters, one for each
phase, accumulate the number of PWM cycles when the phase
current is stepped from zero to full current. At the end of each
phase current rise, the counter for that phase is compared to the
counter for the previous current rise, in the opposite phase. If the
difference is greater than the number in the PWM compare regis-
ter, then the ST bit in the diagnostic registers is set. In addition, if
the ST signal is selected as the output on the DIAG pin, then the
pin will go low.
Automotive, Programmable Stepper Driver
This stall detection scheme assumes a number of factors:
• The motor must be stepping fast enough for the back EMF to
• The motor is not being stepped in full step mode.
• The phase current table must conform to the 0% and ±100%
• The phase current profiles must be the same for both phases.
Although stall detection cannot be guaranteed using this detection
method, good stall detection reliability can be achieved by careful
selection of motor speed, count difference, and by conforming to
the above factors.
In addition to using the integrated features of the A4980, it is
also possible to perform stall detection by examining the PWM
on-time for a single phase using an external microcontroller. In
the A4980 the PWM-on signal for phase A can be selected as the
output on the DIAG pin, by using the serial interface.
reduce the phase current slew rate. Stall detection reliability
improves as the current slew rate reduces.
conditions at steps 0, 16, 32, and 48.
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
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